From 300b124fcf6ad2cd99a7b721e0f096785e0a3134 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Tue, 19 Nov 2019 15:36:14 +0200
Subject: [PATCH 01/20] ovl: fix value of i_ino for lower hardlink corner case

Commit 6dde1e42f497 ("ovl: make i_ino consistent with st_ino in more
cases"), relaxed the condition nfs_export=on in order to set the value of
i_ino to xino map of real ino.

Specifically, it also relaxed the pre-condition that index=on for
consistent i_ino. This opened the corner case of lower hardlink in
ovl_get_inode(), which calls ovl_fill_inode() with ino=0 and then
ovl_init_inode() is called to set i_ino to lower real ino without the xino
mapping.

Pass the correct values of ino;fsid in this case to ovl_fill_inode(), so it
can initialize i_ino correctly.

Fixes: 6dde1e42f497 ("ovl: make i_ino consistent with st_ino in more ...")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/inode.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 79e8994e3bc1..3f993c114829 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -891,7 +891,7 @@ struct inode *ovl_get_inode(struct super_block *sb,
 	struct dentry *lowerdentry = lowerpath ? lowerpath->dentry : NULL;
 	bool bylower = ovl_hash_bylower(sb, upperdentry, lowerdentry,
 					oip->index);
-	int fsid = bylower ? oip->lowerpath->layer->fsid : 0;
+	int fsid = bylower ? lowerpath->layer->fsid : 0;
 	bool is_dir, metacopy = false;
 	unsigned long ino = 0;
 	int err = oip->newinode ? -EEXIST : -ENOMEM;
@@ -941,6 +941,8 @@ struct inode *ovl_get_inode(struct super_block *sb,
 			err = -ENOMEM;
 			goto out_err;
 		}
+		ino = realinode->i_ino;
+		fsid = lowerpath->layer->fsid;
 	}
 	ovl_fill_inode(inode, realinode->i_mode, realinode->i_rdev, ino, fsid);
 	ovl_inode_init(inode, upperdentry, lowerdentry, oip->lowerdata);

From 735c907d7b7df501e951ba07134b9f6f989a94e4 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Tue, 19 Nov 2019 17:14:55 +0200
Subject: [PATCH 02/20] ovl: fix out of date comment and unreachable code

ovl_inode_update() is no longer called from create object code path.

Fixes: 01b39dcc9568 ("ovl: use inode_insert5() to hash a newly...")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/inode.c | 8 +++++---
 fs/overlayfs/util.c  | 2 --
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 3f993c114829..98a605b54e2d 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -571,9 +571,11 @@ static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev,
 	 * bits to encode layer), set the same value used for st_ino to i_ino,
 	 * so inode number exposed via /proc/locks and a like will be
 	 * consistent with d_ino and st_ino values. An i_ino value inconsistent
-	 * with d_ino also causes nfsd readdirplus to fail.  When called from
-	 * ovl_new_inode(), ino arg is 0, so i_ino will be updated to real
-	 * upper inode i_ino on ovl_inode_init() or ovl_inode_update().
+	 * with d_ino also causes nfsd readdirplus to fail.
+	 *
+	 * When called from ovl_create_object() => ovl_new_inode(), with
+	 * ino = 0, i_ino will be updated to consistent value later on in
+	 * ovl_get_inode() => ovl_fill_inode().
 	 */
 	if (ovl_same_dev(inode->i_sb)) {
 		inode->i_ino = ino;
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 042f7eb4f7f4..6584e5800a59 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -416,8 +416,6 @@ void ovl_inode_update(struct inode *inode, struct dentry *upperdentry)
 	smp_wmb();
 	OVL_I(inode)->__upperdentry = upperdentry;
 	if (inode_unhashed(inode)) {
-		if (!inode->i_ino)
-			inode->i_ino = upperinode->i_ino;
 		inode->i_private = upperinode;
 		__insert_inode_hash(inode, (unsigned long) upperinode);
 	}

From 2effc5c25d55b92b89303292128540618f182671 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Tue, 19 Nov 2019 17:49:17 +0200
Subject: [PATCH 03/20] ovl: factor out helper ovl_get_root()

Allocates and initializes the root dentry and inode.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/super.c | 44 +++++++++++++++++++++++++++++---------------
 1 file changed, 29 insertions(+), 15 deletions(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index ac967f1cb6e5..ae9e8b0877f3 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1589,6 +1589,34 @@ static int ovl_check_overlapping_layers(struct super_block *sb,
 	return 0;
 }
 
+static struct dentry *ovl_get_root(struct super_block *sb,
+				   struct dentry *upperdentry,
+				   struct ovl_entry *oe)
+{
+	struct dentry *root;
+
+	root = d_make_root(ovl_new_inode(sb, S_IFDIR, 0));
+	if (!root)
+		return NULL;
+
+	root->d_fsdata = oe;
+
+	if (upperdentry) {
+		ovl_dentry_set_upper_alias(root);
+		if (ovl_is_impuredir(upperdentry))
+			ovl_set_flag(OVL_IMPURE, d_inode(root));
+	}
+
+	/* Root is always merge -> can have whiteouts */
+	ovl_set_flag(OVL_WHITEOUTS, d_inode(root));
+	ovl_dentry_set_flag(OVL_E_CONNECTED, root);
+	ovl_set_upperdata(d_inode(root));
+	ovl_inode_init(d_inode(root), upperdentry, ovl_dentry_lower(root),
+		       NULL);
+
+	return root;
+}
+
 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 {
 	struct path upperpath = { };
@@ -1710,25 +1738,11 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	sb->s_flags |= SB_POSIXACL;
 
 	err = -ENOMEM;
-	root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, 0));
+	root_dentry = ovl_get_root(sb, upperpath.dentry, oe);
 	if (!root_dentry)
 		goto out_free_oe;
 
-	root_dentry->d_fsdata = oe;
-
 	mntput(upperpath.mnt);
-	if (upperpath.dentry) {
-		ovl_dentry_set_upper_alias(root_dentry);
-		if (ovl_is_impuredir(upperpath.dentry))
-			ovl_set_flag(OVL_IMPURE, d_inode(root_dentry));
-	}
-
-	/* Root is always merge -> can have whiteouts */
-	ovl_set_flag(OVL_WHITEOUTS, d_inode(root_dentry));
-	ovl_dentry_set_flag(OVL_E_CONNECTED, root_dentry);
-	ovl_set_upperdata(d_inode(root_dentry));
-	ovl_inode_init(d_inode(root_dentry), upperpath.dentry,
-		       ovl_dentry_lower(root_dentry), NULL);
 
 	sb->s_root = root_dentry;
 

From 62c832ed4e1b67cc65d909005aae5ce7031a2b38 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Tue, 19 Nov 2019 15:31:46 +0200
Subject: [PATCH 04/20] ovl: simplify i_ino initialization

Move i_ino initialization to ovl_inode_init() to avoid the dance of setting
i_ino in ovl_fill_inode() sometimes on the first call and sometimes on the
seconds call.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/inode.c     | 35 ++++++++++++++++++++++++++---------
 fs/overlayfs/overlayfs.h |  4 ++--
 fs/overlayfs/super.c     | 13 +++++++++++--
 fs/overlayfs/util.c      | 18 ------------------
 4 files changed, 39 insertions(+), 31 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 98a605b54e2d..13219a5864c4 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -561,8 +561,7 @@ static inline void ovl_lockdep_annotate_inode_mutex_key(struct inode *inode)
 #endif
 }
 
-static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev,
-			   unsigned long ino, int fsid)
+static void ovl_map_ino(struct inode *inode, unsigned long ino, int fsid)
 {
 	int xinobits = ovl_xino_bits(inode->i_sb);
 
@@ -572,10 +571,6 @@ static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev,
 	 * so inode number exposed via /proc/locks and a like will be
 	 * consistent with d_ino and st_ino values. An i_ino value inconsistent
 	 * with d_ino also causes nfsd readdirplus to fail.
-	 *
-	 * When called from ovl_create_object() => ovl_new_inode(), with
-	 * ino = 0, i_ino will be updated to consistent value later on in
-	 * ovl_get_inode() => ovl_fill_inode().
 	 */
 	if (ovl_same_dev(inode->i_sb)) {
 		inode->i_ino = ino;
@@ -584,6 +579,28 @@ static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev,
 	} else {
 		inode->i_ino = get_next_ino();
 	}
+}
+
+void ovl_inode_init(struct inode *inode, struct ovl_inode_params *oip,
+		    unsigned long ino, int fsid)
+{
+	struct inode *realinode;
+
+	if (oip->upperdentry)
+		OVL_I(inode)->__upperdentry = oip->upperdentry;
+	if (oip->lowerpath && oip->lowerpath->dentry)
+		OVL_I(inode)->lower = igrab(d_inode(oip->lowerpath->dentry));
+	if (oip->lowerdata)
+		OVL_I(inode)->lowerdata = igrab(d_inode(oip->lowerdata));
+
+	realinode = ovl_inode_real(inode);
+	ovl_copyattr(realinode, inode);
+	ovl_copyflags(realinode, inode);
+	ovl_map_ino(inode, ino, fsid);
+}
+
+static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev)
+{
 	inode->i_mode = mode;
 	inode->i_flags |= S_NOCMTIME;
 #ifdef CONFIG_FS_POSIX_ACL
@@ -721,7 +738,7 @@ struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, dev_t rdev)
 
 	inode = new_inode(sb);
 	if (inode)
-		ovl_fill_inode(inode, mode, rdev, 0, 0);
+		ovl_fill_inode(inode, mode, rdev);
 
 	return inode;
 }
@@ -946,8 +963,8 @@ struct inode *ovl_get_inode(struct super_block *sb,
 		ino = realinode->i_ino;
 		fsid = lowerpath->layer->fsid;
 	}
-	ovl_fill_inode(inode, realinode->i_mode, realinode->i_rdev, ino, fsid);
-	ovl_inode_init(inode, upperdentry, lowerdentry, oip->lowerdata);
+	ovl_fill_inode(inode, realinode->i_mode, realinode->i_rdev);
+	ovl_inode_init(inode, oip, ino, fsid);
 
 	if (upperdentry && ovl_is_impuredir(upperdentry))
 		ovl_set_flag(OVL_IMPURE, inode);
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 3d3f2b8bdae5..442fbffe9d7e 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -264,8 +264,6 @@ void ovl_set_upperdata(struct inode *inode);
 bool ovl_redirect_dir(struct super_block *sb);
 const char *ovl_dentry_get_redirect(struct dentry *dentry);
 void ovl_dentry_set_redirect(struct dentry *dentry, const char *redirect);
-void ovl_inode_init(struct inode *inode, struct dentry *upperdentry,
-		    struct dentry *lowerdentry, struct dentry *lowerdata);
 void ovl_inode_update(struct inode *inode, struct dentry *upperdentry);
 void ovl_dir_modified(struct dentry *dentry, bool impurity);
 u64 ovl_dentry_version_get(struct dentry *dentry);
@@ -410,6 +408,8 @@ struct ovl_inode_params {
 	char *redirect;
 	struct dentry *lowerdata;
 };
+void ovl_inode_init(struct inode *inode, struct ovl_inode_params *oip,
+		    unsigned long ino, int fsid);
 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, dev_t rdev);
 struct inode *ovl_lookup_inode(struct super_block *sb, struct dentry *real,
 			       bool is_upper);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index ae9e8b0877f3..4db51c7f48e1 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1594,6 +1594,13 @@ static struct dentry *ovl_get_root(struct super_block *sb,
 				   struct ovl_entry *oe)
 {
 	struct dentry *root;
+	struct ovl_path *lowerpath = &oe->lowerstack[0];
+	unsigned long ino = d_inode(lowerpath->dentry)->i_ino;
+	int fsid = lowerpath->layer->fsid;
+	struct ovl_inode_params oip = {
+		.upperdentry = upperdentry,
+		.lowerpath = lowerpath,
+	};
 
 	root = d_make_root(ovl_new_inode(sb, S_IFDIR, 0));
 	if (!root)
@@ -1602,6 +1609,9 @@ static struct dentry *ovl_get_root(struct super_block *sb,
 	root->d_fsdata = oe;
 
 	if (upperdentry) {
+		/* Root inode uses upper st_ino/i_ino */
+		ino = d_inode(upperdentry)->i_ino;
+		fsid = 0;
 		ovl_dentry_set_upper_alias(root);
 		if (ovl_is_impuredir(upperdentry))
 			ovl_set_flag(OVL_IMPURE, d_inode(root));
@@ -1611,8 +1621,7 @@ static struct dentry *ovl_get_root(struct super_block *sb,
 	ovl_set_flag(OVL_WHITEOUTS, d_inode(root));
 	ovl_dentry_set_flag(OVL_E_CONNECTED, root);
 	ovl_set_upperdata(d_inode(root));
-	ovl_inode_init(d_inode(root), upperdentry, ovl_dentry_lower(root),
-		       NULL);
+	ovl_inode_init(d_inode(root), &oip, ino, fsid);
 
 	return root;
 }
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 6584e5800a59..f318e4811e32 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -386,24 +386,6 @@ void ovl_dentry_set_redirect(struct dentry *dentry, const char *redirect)
 	oi->redirect = redirect;
 }
 
-void ovl_inode_init(struct inode *inode, struct dentry *upperdentry,
-		    struct dentry *lowerdentry, struct dentry *lowerdata)
-{
-	struct inode *realinode = d_inode(upperdentry ?: lowerdentry);
-
-	if (upperdentry)
-		OVL_I(inode)->__upperdentry = upperdentry;
-	if (lowerdentry)
-		OVL_I(inode)->lower = igrab(d_inode(lowerdentry));
-	if (lowerdata)
-		OVL_I(inode)->lowerdata = igrab(d_inode(lowerdata));
-
-	ovl_copyattr(realinode, inode);
-	ovl_copyflags(realinode, inode);
-	if (!inode->i_ino)
-		inode->i_ino = realinode->i_ino;
-}
-
 void ovl_inode_update(struct inode *inode, struct dentry *upperdentry)
 {
 	struct inode *upperinode = d_inode(upperdentry);

From 4c494bd582fa23d2d70851e958da6cee1dc161cb Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 17 Mar 2020 15:04:22 +0100
Subject: [PATCH 05/20] ovl: document permission model

Add missing piece of documentation regarding how permissions are checked in
overlayfs.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 Documentation/filesystems/overlayfs.rst | 44 +++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
index e443be7928db..e398fdf7353e 100644
--- a/Documentation/filesystems/overlayfs.rst
+++ b/Documentation/filesystems/overlayfs.rst
@@ -248,6 +248,50 @@ overlay filesystem (though an operation on the name of the file such as
 rename or unlink will of course be noticed and handled).
 
 
+Permission model
+----------------
+
+Permission checking in the overlay filesystem follows these principles:
+
+ 1) permission check SHOULD return the same result before and after copy up
+
+ 2) task creating the overlay mount MUST NOT gain additional privileges
+
+ 3) non-mounting task MAY gain additional privileges through the overlay,
+ compared to direct access on underlying lower or upper filesystems
+
+This is achieved by performing two permission checks on each access
+
+ a) check if current task is allowed access based on local DAC (owner,
+    group, mode and posix acl), as well as MAC checks
+
+ b) check if mounting task would be allowed real operation on lower or
+    upper layer based on underlying filesystem permissions, again including
+    MAC checks
+
+Check (a) ensures consistency (1) since owner, group, mode and posix acls
+are copied up.  On the other hand it can result in server enforced
+permissions (used by NFS, for example) being ignored (3).
+
+Check (b) ensures that no task gains permissions to underlying layers that
+the mounting task does not have (2).  This also means that it is possible
+to create setups where the consistency rule (1) does not hold; normally,
+however, the mounting task will have sufficient privileges to perform all
+operations.
+
+Another way to demonstrate this model is drawing parallels between
+
+  mount -t overlay overlay -olowerdir=/lower,upperdir=/upper,... /merged
+
+and
+
+  cp -a /lower /upper
+  mount --bind /upper /merged
+
+The resulting access permissions should be the same.  The difference is in
+the time of copy (on-demand vs. up-front).
+
+
 Multiple lower layers
 ---------------------
 

From c61ca5572508516b41039aecb23d936466076950 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 17 Mar 2020 15:04:22 +0100
Subject: [PATCH 06/20] ovl: ignore failure to copy up unknown xattrs

This issue came up with NFSv4 as the lower layer, which generates
"system.nfs4_acl" xattrs (even for plain old unix permissions).  Prior to
this patch this prevented copy-up from succeeding.

The overlayfs permission model mandates that permissions are checked
locally for the task and remotely for the mounter(*).  NFS4 ACLs are not
supported by the Linux kernel currently, hence they cannot be enforced
locally.  Which means it is indifferent whether this attribute is copied or
not.

Generalize this to any xattr that is not used in access checking (i.e. it's
not a POSIX ACL and not in the "security." namespace).

Incidentally, best effort copying of xattrs seems to also be the behavior
of "cp -a", which is what overlayfs tries to mimic.

(*) Documentation/filesystems/overlayfs.txt#Permission model

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/copy_up.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 9fc47c2e078d..9709cf22cab3 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -36,6 +36,13 @@ static int ovl_ccup_get(char *buf, const struct kernel_param *param)
 module_param_call(check_copy_up, ovl_ccup_set, ovl_ccup_get, NULL, 0644);
 MODULE_PARM_DESC(check_copy_up, "Obsolete; does nothing");
 
+static bool ovl_must_copy_xattr(const char *name)
+{
+	return !strcmp(name, XATTR_POSIX_ACL_ACCESS) ||
+	       !strcmp(name, XATTR_POSIX_ACL_DEFAULT) ||
+	       !strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN);
+}
+
 int ovl_copy_xattr(struct dentry *old, struct dentry *new)
 {
 	ssize_t list_size, size, value_size = 0;
@@ -107,8 +114,13 @@ int ovl_copy_xattr(struct dentry *old, struct dentry *new)
 			continue; /* Discard */
 		}
 		error = vfs_setxattr(new, name, value, size, 0);
-		if (error)
-			break;
+		if (error) {
+			if (error != -EOPNOTSUPP || ovl_must_copy_xattr(name))
+				break;
+
+			/* Ignore failure to copy unknown xattrs */
+			error = 0;
+		}
 	}
 	kfree(value);
 out:

From 3bb7df928a7dca0ab5ae143ecffbd8859850cd08 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 17 Mar 2020 15:04:22 +0100
Subject: [PATCH 07/20] ovl: restructure dentry revalidation

Use a common loop for plain and weak revalidation.  This will aid doing
revalidation on upper layer.

This patch doesn't change behavior.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/super.c | 59 ++++++++++++++++++++++----------------------
 1 file changed, 30 insertions(+), 29 deletions(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 4db51c7f48e1..a05bf1179ce0 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -113,45 +113,46 @@ static struct dentry *ovl_d_real(struct dentry *dentry,
 	return dentry;
 }
 
-static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
+static int ovl_revalidate_real(struct dentry *d, unsigned int flags, bool weak)
+{
+	int ret = 1;
+
+	if (weak) {
+		if (d->d_flags & DCACHE_OP_WEAK_REVALIDATE)
+			ret =  d->d_op->d_weak_revalidate(d, flags);
+	} else if (d->d_flags & DCACHE_OP_REVALIDATE) {
+		ret = d->d_op->d_revalidate(d, flags);
+		if (!ret) {
+			if (!(flags & LOOKUP_RCU))
+				d_invalidate(d);
+			ret = -ESTALE;
+		}
+	}
+	return ret;
+}
+
+static int ovl_dentry_revalidate_common(struct dentry *dentry,
+					unsigned int flags, bool weak)
 {
 	struct ovl_entry *oe = dentry->d_fsdata;
 	unsigned int i;
 	int ret = 1;
 
-	for (i = 0; i < oe->numlower; i++) {
-		struct dentry *d = oe->lowerstack[i].dentry;
-
-		if (d->d_flags & DCACHE_OP_REVALIDATE) {
-			ret = d->d_op->d_revalidate(d, flags);
-			if (ret < 0)
-				return ret;
-			if (!ret) {
-				if (!(flags & LOOKUP_RCU))
-					d_invalidate(d);
-				return -ESTALE;
-			}
-		}
+	for (i = 0; ret > 0 && i < oe->numlower; i++) {
+		ret = ovl_revalidate_real(oe->lowerstack[i].dentry, flags,
+					  weak);
 	}
-	return 1;
+	return ret;
+}
+
+static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
+{
+	return ovl_dentry_revalidate_common(dentry, flags, false);
 }
 
 static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
 {
-	struct ovl_entry *oe = dentry->d_fsdata;
-	unsigned int i;
-	int ret = 1;
-
-	for (i = 0; i < oe->numlower; i++) {
-		struct dentry *d = oe->lowerstack[i].dentry;
-
-		if (d->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
-			ret = d->d_op->d_weak_revalidate(d, flags);
-			if (ret <= 0)
-				break;
-		}
-	}
-	return ret;
+	return ovl_dentry_revalidate_common(dentry, flags, true);
 }
 
 static const struct dentry_operations ovl_dentry_operations = {

From 7925dad839e70ab43140e26d6b93e807b5969f05 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 17 Mar 2020 15:04:22 +0100
Subject: [PATCH 08/20] ovl: separate detection of remote upper layer from
 stacked overlay

Following patch will allow remote as upper layer, but not overlay stacked
on upper layer.  Separate the two concepts.

This patch is doesn't change behavior.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/namei.c |  3 ++-
 fs/overlayfs/super.c | 14 +++++++-------
 fs/overlayfs/util.c  |  3 +--
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index ed9e129fae04..a5b998a93a24 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -845,7 +845,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		if (err)
 			goto out;
 
-		if (upperdentry && unlikely(ovl_dentry_remote(upperdentry))) {
+		if (upperdentry && (upperdentry->d_flags & DCACHE_OP_REAL ||
+				    unlikely(ovl_dentry_remote(upperdentry)))) {
 			dput(upperdentry);
 			err = -EREMOTE;
 			goto out;
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index a05bf1179ce0..bc35cd6233ee 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -752,13 +752,13 @@ static int ovl_mount_dir(const char *name, struct path *path)
 		ovl_unescape(tmp);
 		err = ovl_mount_dir_noesc(tmp, path);
 
-		if (!err)
-			if (ovl_dentry_remote(path->dentry)) {
-				pr_err("filesystem on '%s' not supported as upperdir\n",
-				       tmp);
-				path_put_init(path);
-				err = -EINVAL;
-			}
+		if (!err && (ovl_dentry_remote(path->dentry) ||
+			     path->dentry->d_flags & DCACHE_OP_REAL)) {
+			pr_err("filesystem on '%s' not supported as upperdir\n",
+			       tmp);
+			path_put_init(path);
+			err = -EINVAL;
+		}
 		kfree(tmp);
 	}
 	return err;
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index f318e4811e32..997c31509c91 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -93,8 +93,7 @@ struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
 bool ovl_dentry_remote(struct dentry *dentry)
 {
 	return dentry->d_flags &
-		(DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE |
-		 DCACHE_OP_REAL);
+		(DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
 }
 
 bool ovl_dentry_weird(struct dentry *dentry)

From f428884456192230ba1573e4028fb9282ffa2bb7 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 17 Mar 2020 15:04:22 +0100
Subject: [PATCH 09/20] ovl: decide if revalidate needed on a per-dentry basis

Allow completely skipping ->revalidate() on a per-dentry basis, in case the
underlying layers used for a dentry do not themselves have ->revalidate().

E.g. negative overlay dentry has no underlying layers, hence revalidate is
unnecessary.  Or if lower layer is remote but overlay dentry is pure-upper,
then can skip revalidate.

The following places need to update whether the dentry needs revalidate or
not:

 - fill-super (root dentry)
 - lookup
 - create
 - fh_to_dentry

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/dir.c       |  3 +++
 fs/overlayfs/export.c    |  2 ++
 fs/overlayfs/namei.c     |  3 +++
 fs/overlayfs/overlayfs.h |  2 ++
 fs/overlayfs/super.c     | 21 +++++----------------
 fs/overlayfs/util.c      | 15 +++++++++++++++
 6 files changed, 30 insertions(+), 16 deletions(-)

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 8e57d5372b8f..b3471ef51440 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -243,6 +243,9 @@ static int ovl_instantiate(struct dentry *dentry, struct inode *inode,
 
 	ovl_dir_modified(dentry->d_parent, false);
 	ovl_dentry_set_upper_alias(dentry);
+	ovl_dentry_update_reval(dentry, newdentry,
+			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
+
 	if (!hardlink) {
 		/*
 		 * ovl_obtain_alias() can be called after ovl_create_real()
diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index 6f54d70cef27..a58b3d9b06b9 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -324,6 +324,8 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
 		if (upper_alias)
 			ovl_dentry_set_upper_alias(dentry);
 	}
+	ovl_dentry_update_reval(dentry, upper,
+			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
 
 	return d_instantiate_anon(dentry, inode);
 
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index a5b998a93a24..76e61cc27822 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -1077,6 +1077,9 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			goto out_free_oe;
 	}
 
+	ovl_dentry_update_reval(dentry, upperdentry,
+			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
+
 	revert_creds(old_cred);
 	if (origin_path) {
 		dput(origin_path->dentry);
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 442fbffe9d7e..70d17040ab4d 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -230,6 +230,8 @@ bool ovl_index_all(struct super_block *sb);
 bool ovl_verify_lower(struct super_block *sb);
 struct ovl_entry *ovl_alloc_entry(unsigned int numlower);
 bool ovl_dentry_remote(struct dentry *dentry);
+void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *upperdentry,
+			     unsigned int mask);
 bool ovl_dentry_weird(struct dentry *dentry);
 enum ovl_path_type ovl_path_type(struct dentry *dentry);
 void ovl_path_upper(struct dentry *dentry, struct path *path);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index bc35cd6233ee..d944ab46b69e 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -158,11 +158,6 @@ static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
 static const struct dentry_operations ovl_dentry_operations = {
 	.d_release = ovl_dentry_release,
 	.d_real = ovl_d_real,
-};
-
-static const struct dentry_operations ovl_reval_dentry_operations = {
-	.d_release = ovl_dentry_release,
-	.d_real = ovl_d_real,
 	.d_revalidate = ovl_dentry_revalidate,
 	.d_weak_revalidate = ovl_dentry_weak_revalidate,
 };
@@ -779,7 +774,7 @@ static int ovl_check_namelen(struct path *path, struct ovl_fs *ofs,
 }
 
 static int ovl_lower_dir(const char *name, struct path *path,
-			 struct ovl_fs *ofs, int *stack_depth, bool *remote)
+			 struct ovl_fs *ofs, int *stack_depth)
 {
 	int fh_type;
 	int err;
@@ -794,9 +789,6 @@ static int ovl_lower_dir(const char *name, struct path *path,
 
 	*stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
 
-	if (ovl_dentry_remote(path->dentry))
-		*remote = true;
-
 	/*
 	 * The inodes index feature and NFS export need to encode and decode
 	 * file handles, so they require that all layers support them.
@@ -1441,7 +1433,6 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 	char *lowertmp, *lower;
 	struct path *stack = NULL;
 	unsigned int stacklen, numlower = 0, i;
-	bool remote = false;
 	struct ovl_entry *oe;
 
 	err = -ENOMEM;
@@ -1473,7 +1464,7 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 	lower = lowertmp;
 	for (numlower = 0; numlower < stacklen; numlower++) {
 		err = ovl_lower_dir(lower, &stack[numlower], ofs,
-				    &sb->s_stack_depth, &remote);
+				    &sb->s_stack_depth);
 		if (err)
 			goto out_err;
 
@@ -1501,11 +1492,6 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 		oe->lowerstack[i].layer = &ofs->layers[i+1];
 	}
 
-	if (remote)
-		sb->s_d_op = &ovl_reval_dentry_operations;
-	else
-		sb->s_d_op = &ovl_dentry_operations;
-
 out:
 	for (i = 0; i < numlower; i++)
 		path_put(&stack[i]);
@@ -1623,6 +1609,7 @@ static struct dentry *ovl_get_root(struct super_block *sb,
 	ovl_dentry_set_flag(OVL_E_CONNECTED, root);
 	ovl_set_upperdata(d_inode(root));
 	ovl_inode_init(d_inode(root), &oip, ino, fsid);
+	ovl_dentry_update_reval(root, upperdentry, DCACHE_OP_WEAK_REVALIDATE);
 
 	return root;
 }
@@ -1636,6 +1623,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	struct cred *cred;
 	int err;
 
+	sb->s_d_op = &ovl_dentry_operations;
+
 	err = -ENOMEM;
 	ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
 	if (!ofs)
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 997c31509c91..1cd805ba1eeb 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -96,6 +96,21 @@ bool ovl_dentry_remote(struct dentry *dentry)
 		(DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
 }
 
+void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *upperdentry,
+			     unsigned int mask)
+{
+	struct ovl_entry *oe = OVL_E(dentry);
+	unsigned int i, flags = 0;
+
+	for (i = 0; i < oe->numlower; i++)
+		flags |= oe->lowerstack[i].dentry->d_flags;
+
+	spin_lock(&dentry->d_lock);
+	dentry->d_flags &= ~mask;
+	dentry->d_flags |= flags & mask;
+	spin_unlock(&dentry->d_lock);
+}
+
 bool ovl_dentry_weird(struct dentry *dentry)
 {
 	return dentry->d_flags & (DCACHE_NEED_AUTOMOUNT |

From bccece1ead368149f90e05ad104dfbfda4422f5d Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 17 Mar 2020 15:04:22 +0100
Subject: [PATCH 10/20] ovl: allow remote upper

No reason to prevent upper layer being a remote filesystem.  Do the
revalidation in that case, just as we already do for lower layers.

This lets virtiofs be used as upper layer, which appears to be a real use
case.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/namei.c | 3 +--
 fs/overlayfs/super.c | 8 ++++++--
 fs/overlayfs/util.c  | 2 ++
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 76e61cc27822..0db23baf98e7 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -845,8 +845,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		if (err)
 			goto out;
 
-		if (upperdentry && (upperdentry->d_flags & DCACHE_OP_REAL ||
-				    unlikely(ovl_dentry_remote(upperdentry)))) {
+		if (upperdentry && upperdentry->d_flags & DCACHE_OP_REAL) {
 			dput(upperdentry);
 			err = -EREMOTE;
 			goto out;
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index d944ab46b69e..e8965fd1a608 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -135,9 +135,14 @@ static int ovl_dentry_revalidate_common(struct dentry *dentry,
 					unsigned int flags, bool weak)
 {
 	struct ovl_entry *oe = dentry->d_fsdata;
+	struct dentry *upper;
 	unsigned int i;
 	int ret = 1;
 
+	upper = ovl_dentry_upper(dentry);
+	if (upper)
+		ret = ovl_revalidate_real(upper, flags, weak);
+
 	for (i = 0; ret > 0 && i < oe->numlower; i++) {
 		ret = ovl_revalidate_real(oe->lowerstack[i].dentry, flags,
 					  weak);
@@ -747,8 +752,7 @@ static int ovl_mount_dir(const char *name, struct path *path)
 		ovl_unescape(tmp);
 		err = ovl_mount_dir_noesc(tmp, path);
 
-		if (!err && (ovl_dentry_remote(path->dentry) ||
-			     path->dentry->d_flags & DCACHE_OP_REAL)) {
+		if (!err && path->dentry->d_flags & DCACHE_OP_REAL) {
 			pr_err("filesystem on '%s' not supported as upperdir\n",
 			       tmp);
 			path_put_init(path);
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 1cd805ba1eeb..36b60788ee47 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -102,6 +102,8 @@ void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *upperdentry,
 	struct ovl_entry *oe = OVL_E(dentry);
 	unsigned int i, flags = 0;
 
+	if (upperdentry)
+		flags |= upperdentry->d_flags;
 	for (i = 0; i < oe->numlower; i++)
 		flags |= oe->lowerstack[i].dentry->d_flags;
 

From cad218ab3320789ea4621c15e56b8114a4160bab Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Thu, 20 Feb 2020 09:00:19 +0200
Subject: [PATCH 11/20] ovl: check if upper fs supports RENAME_WHITEOUT

As with other required upper fs features, we only warn if support is
missing to avoid breaking existing sub-optimal setups.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/dir.c       |  2 +-
 fs/overlayfs/overlayfs.h |  1 +
 fs/overlayfs/super.c     | 69 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index b3471ef51440..c91b5aae8e32 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -42,7 +42,7 @@ int ovl_cleanup(struct inode *wdir, struct dentry *wdentry)
 	return err;
 }
 
-static struct dentry *ovl_lookup_temp(struct dentry *workdir)
+struct dentry *ovl_lookup_temp(struct dentry *workdir)
 {
 	struct dentry *temp;
 	char name[20];
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 70d17040ab4d..ea531b1075f2 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -453,6 +453,7 @@ struct ovl_cattr {
 struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
 			       struct ovl_cattr *attr);
 int ovl_cleanup(struct inode *dir, struct dentry *dentry);
+struct dentry *ovl_lookup_temp(struct dentry *workdir);
 struct dentry *ovl_create_temp(struct dentry *workdir, struct ovl_cattr *attr);
 
 /* file.c */
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index e8965fd1a608..b6ecaf95db9f 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1071,6 +1071,66 @@ static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
 	return err;
 }
 
+/*
+ * Returns 1 if RENAME_WHITEOUT is supported, 0 if not supported and
+ * negative values if error is encountered.
+ */
+static int ovl_check_rename_whiteout(struct dentry *workdir)
+{
+	struct inode *dir = d_inode(workdir);
+	struct dentry *temp;
+	struct dentry *dest;
+	struct dentry *whiteout;
+	struct name_snapshot name;
+	int err;
+
+	inode_lock_nested(dir, I_MUTEX_PARENT);
+
+	temp = ovl_create_temp(workdir, OVL_CATTR(S_IFREG | 0));
+	err = PTR_ERR(temp);
+	if (IS_ERR(temp))
+		goto out_unlock;
+
+	dest = ovl_lookup_temp(workdir);
+	err = PTR_ERR(dest);
+	if (IS_ERR(dest)) {
+		dput(temp);
+		goto out_unlock;
+	}
+
+	/* Name is inline and stable - using snapshot as a copy helper */
+	take_dentry_name_snapshot(&name, temp);
+	err = ovl_do_rename(dir, temp, dir, dest, RENAME_WHITEOUT);
+	if (err) {
+		if (err == -EINVAL)
+			err = 0;
+		goto cleanup_temp;
+	}
+
+	whiteout = lookup_one_len(name.name.name, workdir, name.name.len);
+	err = PTR_ERR(whiteout);
+	if (IS_ERR(whiteout))
+		goto cleanup_temp;
+
+	err = ovl_is_whiteout(whiteout);
+
+	/* Best effort cleanup of whiteout and temp file */
+	if (err)
+		ovl_cleanup(dir, whiteout);
+	dput(whiteout);
+
+cleanup_temp:
+	ovl_cleanup(dir, temp);
+	release_dentry_name_snapshot(&name);
+	dput(temp);
+	dput(dest);
+
+out_unlock:
+	inode_unlock(dir);
+
+	return err;
+}
+
 static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 			    struct path *workpath)
 {
@@ -1116,6 +1176,15 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 	else
 		pr_warn("upper fs does not support tmpfile.\n");
 
+
+	/* Check if upper/work fs supports RENAME_WHITEOUT */
+	err = ovl_check_rename_whiteout(ofs->workdir);
+	if (err < 0)
+		goto out;
+
+	if (!err)
+		pr_warn("upper fs does not support RENAME_WHITEOUT.\n");
+
 	/*
 	 * Check if upper/work fs supports trusted.overlay.* xattr
 	 */

From d80172c2d85947efe285693c5cea9c8976f478bf Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Thu, 20 Feb 2020 09:03:08 +0200
Subject: [PATCH 12/20] ovl: strict upper fs requirements for remote upper fs

Overlayfs works sub-optimally with upper fs that has no xattr/d_type/
RENAME_WHITEOUT support. We should basically deprecate support for those
filesystems, but so far, we only issue a warning and don't fail the mount
for the sake of backward compat.  Some features are already being disabled
with no xattr support.

For newly supported remote upper fs, we do not need to worry about backward
compatibility, so we can fail the mount if upper fs is a sub-optimal
filesystem.

This reduces the in-tree remote filesystems supported as upper to just
FUSE, for which the remote upper fs support was added.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/super.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index b6ecaf95db9f..ac013ed97a53 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1136,6 +1136,8 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 {
 	struct vfsmount *mnt = ofs->upper_mnt;
 	struct dentry *temp;
+	bool rename_whiteout;
+	bool d_type;
 	int fh_type;
 	int err;
 
@@ -1161,11 +1163,8 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 	if (err < 0)
 		goto out;
 
-	/*
-	 * We allowed this configuration and don't want to break users over
-	 * kernel upgrade. So warn instead of erroring out.
-	 */
-	if (!err)
+	d_type = err;
+	if (!d_type)
 		pr_warn("upper fs needs to support d_type.\n");
 
 	/* Check if upper/work fs supports O_TMPFILE */
@@ -1182,7 +1181,8 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 	if (err < 0)
 		goto out;
 
-	if (!err)
+	rename_whiteout = err;
+	if (!rename_whiteout)
 		pr_warn("upper fs does not support RENAME_WHITEOUT.\n");
 
 	/*
@@ -1199,6 +1199,18 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
 		vfs_removexattr(ofs->workdir, OVL_XATTR_OPAQUE);
 	}
 
+	/*
+	 * We allowed sub-optimal upper fs configuration and don't want to break
+	 * users over kernel upgrade, but we never allowed remote upper fs, so
+	 * we can enforce strict requirements for remote upper fs.
+	 */
+	if (ovl_dentry_remote(ofs->workdir) &&
+	    (!d_type || !rename_whiteout || ofs->noxattr)) {
+		pr_err("upper fs missing required features.\n");
+		err = -EINVAL;
+		goto out;
+	}
+
 	/* Check if upper/work fs supports file handles */
 	fh_type = ovl_can_decode_fh(ofs->workdir->d_sb);
 	if (ofs->config.index && !fh_type) {

From 504f38410a51f513606c3c18c7f6a32c1ca2afb5 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Thu, 24 Oct 2019 02:06:45 +0100
Subject: [PATCH 13/20] ovl: ovl_obtain_alias(): don't call
 d_instantiate_anon() for old

The situation is the same as for __d_obtain_alias() (which is what that
thing is parallel to) - if we find a preexisting alias, we want to grab it,
drop the inode and return the alias we'd found.

The only thing d_instantiate_anon() does compared to that is spurious
security_d_instiate() that has already been done to that dentry with exact
same arguments.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/export.c | 36 ++++++++++++++++++++----------------
 1 file changed, 20 insertions(+), 16 deletions(-)

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index a58b3d9b06b9..475c61f53f0f 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -308,31 +308,35 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
 		ovl_set_flag(OVL_UPPERDATA, inode);
 
 	dentry = d_find_any_alias(inode);
-	if (!dentry) {
-		dentry = d_alloc_anon(inode->i_sb);
-		if (!dentry)
-			goto nomem;
-		oe = ovl_alloc_entry(lower ? 1 : 0);
-		if (!oe)
-			goto nomem;
+	if (dentry)
+		goto out_iput;
 
-		if (lower) {
-			oe->lowerstack->dentry = dget(lower);
-			oe->lowerstack->layer = lowerpath->layer;
-		}
-		dentry->d_fsdata = oe;
-		if (upper_alias)
-			ovl_dentry_set_upper_alias(dentry);
+	dentry = d_alloc_anon(inode->i_sb);
+	if (unlikely(!dentry))
+		goto nomem;
+	oe = ovl_alloc_entry(lower ? 1 : 0);
+	if (!oe)
+		goto nomem;
+
+	if (lower) {
+		oe->lowerstack->dentry = dget(lower);
+		oe->lowerstack->layer = lowerpath->layer;
 	}
+	dentry->d_fsdata = oe;
+	if (upper_alias)
+		ovl_dentry_set_upper_alias(dentry);
+
 	ovl_dentry_update_reval(dentry, upper,
 			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
 
 	return d_instantiate_anon(dentry, inode);
 
 nomem:
-	iput(inode);
 	dput(dentry);
-	return ERR_PTR(-ENOMEM);
+	dentry = ERR_PTR(-ENOMEM);
+out_iput:
+	iput(inode);
+	return dentry;
 }
 
 /* Get the upper or lower dentry in stach whose on layer @idx */

From 0efbe7c4f948eb1233ef52c1cdba0b4ff973df36 Mon Sep 17 00:00:00 2001
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Mon, 9 Mar 2020 15:22:33 -0500
Subject: [PATCH 14/20] ovl: replace zero-length array with flexible-array
 member

The current codebase makes use of the zero-length array language extension
to the C90 standard, but the preferred mechanism to declare variable-length
types such as these ones is a flexible array member[1][2], introduced in
C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning in
case the flexible array does not occur last in the structure, which will
help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by this
change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Fixes: cbe7fba8edfc ("ovl: make sure that real fid is 32bit aligned in memory")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/overlayfs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index ea531b1075f2..e81fea86139e 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -87,7 +87,7 @@ struct ovl_fb {
 	u8 flags;	/* OVL_FH_FLAG_* */
 	u8 type;	/* fid_type of fid */
 	uuid_t uuid;	/* uuid of filesystem */
-	u32 fid[0];	/* file identifier should be 32bit aligned in-memory */
+	u32 fid[];	/* file identifier should be 32bit aligned in-memory */
 } __packed;
 
 /* In-memory and on-wire format for overlay file handle */

From a5a84682ecb67e74d1f265d1634c146c990e0e4f Mon Sep 17 00:00:00 2001
From: Chengguang Xu <cgxu519@mykernel.net>
Date: Mon, 10 Feb 2020 11:11:14 +0800
Subject: [PATCH 15/20] ovl: fix a typo in comment

Fix a typo in comment. (annonate -> annotate)

Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 13219a5864c4..956c6f9c9c11 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -504,7 +504,7 @@ static const struct address_space_operations ovl_aops = {
 
 /*
  * It is possible to stack overlayfs instance on top of another
- * overlayfs instance as lower layer. We need to annonate the
+ * overlayfs instance as lower layer. We need to annotate the
  * stackable i_mutex locks according to stack level of the super
  * block instance. An overlayfs instance can never be in stack
  * depth 0 (there is always a real fs below it).  An overlayfs

From 83552eacdfc06378b0993a3705833c1fd0aead4b Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Fri, 27 Mar 2020 16:51:02 +0100
Subject: [PATCH 16/20] ovl: fix WARN_ON nlink drop to zero

Changes to underlying layers should not cause WARN_ON(), but this repro
does:

 mkdir w l u mnt
 sudo mount -t overlay -o workdir=w,lowerdir=l,upperdir=u overlay mnt
 touch mnt/h
 ln u/h u/k
 rm -rf mnt/k
 rm -rf mnt/h
 dmesg

 ------------[ cut here ]------------
 WARNING: CPU: 1 PID: 116244 at fs/inode.c:302 drop_nlink+0x28/0x40

After upper hardlinks were added while overlay is mounted, unlinking all
overlay hardlinks drops overlay nlink to zero before all upper inodes
are unlinked.

After unlink/rename prevent i_nlink from going to zero if there are still
hashed aliases (i.e. cached hard links to the victim) remaining.

Reported-by: Phasip <phasip@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/dir.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index c91b5aae8e32..279009dee366 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -822,6 +822,28 @@ static bool ovl_pure_upper(struct dentry *dentry)
 	       !ovl_test_flag(OVL_WHITEOUTS, d_inode(dentry));
 }
 
+static void ovl_drop_nlink(struct dentry *dentry)
+{
+	struct inode *inode = d_inode(dentry);
+	struct dentry *alias;
+
+	/* Try to find another, hashed alias */
+	spin_lock(&inode->i_lock);
+	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+		if (alias != dentry && !d_unhashed(alias))
+			break;
+	}
+	spin_unlock(&inode->i_lock);
+
+	/*
+	 * Changes to underlying layers may cause i_nlink to lose sync with
+	 * reality.  In this case prevent the link count from going to zero
+	 * prematurely.
+	 */
+	if (inode->i_nlink > !!alias)
+		drop_nlink(inode);
+}
+
 static int ovl_do_remove(struct dentry *dentry, bool is_dir)
 {
 	int err;
@@ -859,7 +881,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
 		if (is_dir)
 			clear_nlink(dentry->d_inode);
 		else
-			drop_nlink(dentry->d_inode);
+			ovl_drop_nlink(dentry);
 	}
 	ovl_nlink_end(dentry);
 
@@ -1204,7 +1226,7 @@ static int ovl_rename(struct inode *olddir, struct dentry *old,
 		if (new_is_dir)
 			clear_nlink(d_inode(new));
 		else
-			drop_nlink(d_inode(new));
+			ovl_drop_nlink(new);
 	}
 
 	ovl_dir_modified(old->d_parent, ovl_type_origin(old) ||

From 4d314f7859dc1925ee28b4d4e74f6f3a80e6f34b Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Fri, 21 Feb 2020 16:34:43 +0200
Subject: [PATCH 17/20] ovl: use a private non-persistent ino pool

There is no reason to deplete the system's global get_next_ino() pool for
overlay non-persistent inode numbers and there is no reason at all to
allocate non-persistent inode numbers for non-directories.

For non-directories, it is much better to leave i_ino the same as real
i_ino, to be consistent with st_ino/d_ino.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/inode.c     | 15 ++++++++++++---
 fs/overlayfs/ovl_entry.h |  2 ++
 fs/overlayfs/super.c     |  1 +
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 956c6f9c9c11..8130ae54a332 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -561,6 +561,15 @@ static inline void ovl_lockdep_annotate_inode_mutex_key(struct inode *inode)
 #endif
 }
 
+static void ovl_next_ino(struct inode *inode)
+{
+	struct ovl_fs *ofs = inode->i_sb->s_fs_info;
+
+	inode->i_ino = atomic_long_inc_return(&ofs->last_ino);
+	if (unlikely(!inode->i_ino))
+		inode->i_ino = atomic_long_inc_return(&ofs->last_ino);
+}
+
 static void ovl_map_ino(struct inode *inode, unsigned long ino, int fsid)
 {
 	int xinobits = ovl_xino_bits(inode->i_sb);
@@ -572,12 +581,12 @@ static void ovl_map_ino(struct inode *inode, unsigned long ino, int fsid)
 	 * consistent with d_ino and st_ino values. An i_ino value inconsistent
 	 * with d_ino also causes nfsd readdirplus to fail.
 	 */
+	inode->i_ino = ino;
 	if (ovl_same_dev(inode->i_sb)) {
-		inode->i_ino = ino;
 		if (xinobits && fsid && !(ino >> (64 - xinobits)))
 			inode->i_ino |= (unsigned long)fsid << (64 - xinobits);
-	} else {
-		inode->i_ino = get_next_ino();
+	} else if (S_ISDIR(inode->i_mode)) {
+		ovl_next_ino(inode);
 	}
 }
 
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 89015ea822e7..5762d802fe01 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -75,6 +75,8 @@ struct ovl_fs {
 	struct inode *indexdir_trap;
 	/* -1: disabled, 0: same fs, 1..32: number of unused ino bits */
 	int xino_mode;
+	/* For allocation of non-persistent inode numbers */
+	atomic_long_t last_ino;
 };
 
 static inline struct ovl_fs *OVL_FS(struct super_block *sb)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index ac013ed97a53..1f1d40fc5e33 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1736,6 +1736,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
 	sb->s_stack_depth = 0;
 	sb->s_maxbytes = MAX_LFS_FILESIZE;
+	atomic_long_set(&ofs->last_ino, 1);
 	/* Assume underlaying fs uses 32bit inodes unless proven otherwise */
 	if (ofs->config.xino != OVL_XINO_OFF) {
 		ofs->xino_mode = BITS_PER_LONG - 32;

From dfe51d47b7eeb5642ed92558b62eeff558f00eda Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Fri, 21 Feb 2020 16:34:44 +0200
Subject: [PATCH 18/20] ovl: avoid possible inode number collisions with
 xino=on

When xino feature is enabled and a real directory inode number overflows
the lower xino bits, we cannot map this directory inode number to a unique
and persistent inode number and we fall back to the real inode st_ino and
overlay st_dev.

The real inode st_ino with high bits may collide with a lower inode number
on overlay st_dev that was mapped using xino.

To avoid possible collision with legitimate xino values, map a non
persistent inode number to a dedicated range in the xino address space.
The dedicated range is created by adding one more bit to the number of
reserved high xino bits.  We could have added just one more fsid, but that
would have had the undesired effect of changing persistent overlay inode
numbers on kernel or require more complex xino mapping code.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/inode.c   | 39 +++++++++++++++++++++++++++++----------
 fs/overlayfs/readdir.c | 10 ++++++++--
 fs/overlayfs/super.c   | 13 ++++++++-----
 3 files changed, 45 insertions(+), 17 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 8130ae54a332..2d6251a4caaf 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -79,6 +79,7 @@ static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat, int fsid)
 {
 	bool samefs = ovl_same_fs(dentry->d_sb);
 	unsigned int xinobits = ovl_xino_bits(dentry->d_sb);
+	unsigned int xinoshift = 64 - xinobits;
 
 	if (samefs) {
 		/*
@@ -89,20 +90,20 @@ static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat, int fsid)
 		stat->dev = dentry->d_sb->s_dev;
 		return 0;
 	} else if (xinobits) {
-		unsigned int shift = 64 - xinobits;
 		/*
 		 * All inode numbers of underlying fs should not be using the
 		 * high xinobits, so we use high xinobits to partition the
 		 * overlay st_ino address space. The high bits holds the fsid
-		 * (upper fsid is 0). This way overlay inode numbers are unique
-		 * and all inodes use overlay st_dev. Inode numbers are also
-		 * persistent for a given layer configuration.
+		 * (upper fsid is 0). The lowest xinobit is reserved for mapping
+		 * the non-peresistent inode numbers range in case of overflow.
+		 * This way all overlay inode numbers are unique and use the
+		 * overlay st_dev.
 		 */
-		if (stat->ino >> shift) {
+		if (unlikely(stat->ino >> xinoshift)) {
 			pr_warn_ratelimited("inode number too big (%pd2, ino=%llu, xinobits=%d)\n",
 					    dentry, stat->ino, xinobits);
 		} else {
-			stat->ino |= ((u64)fsid) << shift;
+			stat->ino |= ((u64)fsid) << (xinoshift + 1);
 			stat->dev = dentry->d_sb->s_dev;
 			return 0;
 		}
@@ -573,6 +574,7 @@ static void ovl_next_ino(struct inode *inode)
 static void ovl_map_ino(struct inode *inode, unsigned long ino, int fsid)
 {
 	int xinobits = ovl_xino_bits(inode->i_sb);
+	unsigned int xinoshift = 64 - xinobits;
 
 	/*
 	 * When d_ino is consistent with st_ino (samefs or i_ino has enough
@@ -582,11 +584,28 @@ static void ovl_map_ino(struct inode *inode, unsigned long ino, int fsid)
 	 * with d_ino also causes nfsd readdirplus to fail.
 	 */
 	inode->i_ino = ino;
-	if (ovl_same_dev(inode->i_sb)) {
-		if (xinobits && fsid && !(ino >> (64 - xinobits)))
-			inode->i_ino |= (unsigned long)fsid << (64 - xinobits);
-	} else if (S_ISDIR(inode->i_mode)) {
+	if (ovl_same_fs(inode->i_sb)) {
+		return;
+	} else if (xinobits && likely(!(ino >> xinoshift))) {
+		inode->i_ino |= (unsigned long)fsid << (xinoshift + 1);
+		return;
+	}
+
+	/*
+	 * For directory inodes on non-samefs with xino disabled or xino
+	 * overflow, we allocate a non-persistent inode number, to be used for
+	 * resolving st_ino collisions in ovl_map_dev_ino().
+	 *
+	 * To avoid ino collision with legitimate xino values from upper
+	 * layer (fsid 0), use the lowest xinobit to map the non
+	 * persistent inode numbers to the unified st_ino address space.
+	 */
+	if (S_ISDIR(inode->i_mode)) {
 		ovl_next_ino(inode);
+		if (xinobits) {
+			inode->i_ino &= ~0UL >> xinobits;
+			inode->i_ino |= 1UL << xinoshift;
+		}
 	}
 }
 
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 40ac9ce2465a..6325dcc4c48b 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -440,13 +440,19 @@ static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
 static u64 ovl_remap_lower_ino(u64 ino, int xinobits, int fsid,
 			       const char *name, int namelen)
 {
-	if (ino >> (64 - xinobits)) {
+	unsigned int xinoshift = 64 - xinobits;
+
+	if (unlikely(ino >> xinoshift)) {
 		pr_warn_ratelimited("d_ino too big (%.*s, ino=%llu, xinobits=%d)\n",
 				    namelen, name, ino, xinobits);
 		return ino;
 	}
 
-	return ino | ((u64)fsid) << (64 - xinobits);
+	/*
+	 * The lowest xinobit is reserved for mapping the non-peresistent inode
+	 * numbers range, but this range is only exposed via st_ino, not here.
+	 */
+	return ino | ((u64)fsid) << (xinoshift + 1);
 }
 
 /*
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 1f1d40fc5e33..53dd094f970e 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1483,7 +1483,8 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 	 * free high bits in underlying fs to hold the unique fsid.
 	 * If overlayfs does encounter underlying inodes using the high xino
 	 * bits reserved for fsid, it emits a warning and uses the original
-	 * inode number.
+	 * inode number or a non persistent inode number allocated from a
+	 * dedicated range.
 	 */
 	if (ofs->numfs - !ofs->upper_mnt == 1) {
 		if (ofs->config.xino == OVL_XINO_ON)
@@ -1494,11 +1495,13 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 	} else if (ofs->config.xino == OVL_XINO_ON && ofs->xino_mode < 0) {
 		/*
 		 * This is a roundup of number of bits needed for encoding
-		 * fsid, where fsid 0 is reserved for upper fs even with
-		 * lower only overlay.
+		 * fsid, where fsid 0 is reserved for upper fs (even with
+		 * lower only overlay) +1 extra bit is reserved for the non
+		 * persistent inode number range that is used for resolving
+		 * xino lower bits overflow.
 		 */
-		BUILD_BUG_ON(ilog2(OVL_MAX_STACK) > 31);
-		ofs->xino_mode = ilog2(ofs->numfs - 1) + 1;
+		BUILD_BUG_ON(ilog2(OVL_MAX_STACK) > 30);
+		ofs->xino_mode = ilog2(ofs->numfs - 1) + 2;
 	}
 
 	if (ofs->xino_mode > 0) {

From 926e94d79baf76ce7a4d26c3116b6d85a77a475b Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Fri, 21 Feb 2020 16:34:45 +0200
Subject: [PATCH 19/20] ovl: enable xino automatically in more cases

So far, with xino=auto, we only enable xino if we know that all
underlying filesystem use 32bit inode numbers.

When users configure overlay with xino=auto, they already declare that
they are ready to handle 64bit inode number from overlay.

It is a very common case, that underlying filesystem uses 64bit ino,
but rarely or never uses the high inode number bits (e.g. tmpfs, xfs).
Leaving it for the users to declare high ino bits are unused with
xino=on is not a recipe for many users to enjoy the benefits of xino.

There appears to be very little reason not to enable xino when users
declare xino=auto even if we do not know how many bits underlying
filesystem uses for inode numbers.

In the worst case of xino bits overflow by real inode number, we
already fall back to the non-xino behavior - real inode number with
unique pseudo dev or to non persistent inode number and overlay st_dev
(for directories).

The only annoyance from auto enabling xino is that xino bits overflow
emits a warning to kmsg. Suppress those warnings unless users explicitly
asked for xino=on, suggesting that they expected high ino bits to be
unused by underlying filesystem.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/inode.c     |  8 ++++----
 fs/overlayfs/overlayfs.h | 16 ++++++++++++++++
 fs/overlayfs/readdir.c   | 15 ++++++++++-----
 fs/overlayfs/super.c     | 12 +++---------
 4 files changed, 33 insertions(+), 18 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 2d6251a4caaf..b0d42ece4d7c 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -99,13 +99,13 @@ static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat, int fsid)
 		 * This way all overlay inode numbers are unique and use the
 		 * overlay st_dev.
 		 */
-		if (unlikely(stat->ino >> xinoshift)) {
-			pr_warn_ratelimited("inode number too big (%pd2, ino=%llu, xinobits=%d)\n",
-					    dentry, stat->ino, xinobits);
-		} else {
+		if (likely(!(stat->ino >> xinoshift))) {
 			stat->ino |= ((u64)fsid) << (xinoshift + 1);
 			stat->dev = dentry->d_sb->s_dev;
 			return 0;
+		} else if (ovl_xino_warn(dentry->d_sb)) {
+			pr_warn_ratelimited("inode number too big (%pd2, ino=%llu, xinobits=%d)\n",
+					    dentry, stat->ino, xinobits);
 		}
 	}
 
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index e81fea86139e..e6f3670146ed 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -48,6 +48,12 @@ enum ovl_entry_flag {
 	OVL_E_CONNECTED,
 };
 
+enum {
+	OVL_XINO_OFF,
+	OVL_XINO_AUTO,
+	OVL_XINO_ON,
+};
+
 /*
  * The tuple (fh,uuid) is a universal unique identifier for a copy up origin,
  * where:
@@ -301,6 +307,16 @@ static inline bool ovl_is_impuredir(struct dentry *dentry)
 	return ovl_check_dir_xattr(dentry, OVL_XATTR_IMPURE);
 }
 
+/*
+ * With xino=auto, we do best effort to keep all inodes on same st_dev and
+ * d_ino consistent with st_ino.
+ * With xino=on, we do the same effort but we warn if we failed.
+ */
+static inline bool ovl_xino_warn(struct super_block *sb)
+{
+	return OVL_FS(sb)->config.xino == OVL_XINO_ON;
+}
+
 /* All layers on same fs? */
 static inline bool ovl_same_fs(struct super_block *sb)
 {
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 6325dcc4c48b..e452ff7d583d 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -438,13 +438,15 @@ static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
 
 /* Map inode number to lower fs unique range */
 static u64 ovl_remap_lower_ino(u64 ino, int xinobits, int fsid,
-			       const char *name, int namelen)
+			       const char *name, int namelen, bool warn)
 {
 	unsigned int xinoshift = 64 - xinobits;
 
 	if (unlikely(ino >> xinoshift)) {
-		pr_warn_ratelimited("d_ino too big (%.*s, ino=%llu, xinobits=%d)\n",
-				    namelen, name, ino, xinobits);
+		if (warn) {
+			pr_warn_ratelimited("d_ino too big (%.*s, ino=%llu, xinobits=%d)\n",
+					    namelen, name, ino, xinobits);
+		}
 		return ino;
 	}
 
@@ -521,7 +523,8 @@ static int ovl_cache_update_ino(struct path *path, struct ovl_cache_entry *p)
 	} else if (xinobits && !OVL_TYPE_UPPER(type)) {
 		ino = ovl_remap_lower_ino(ino, xinobits,
 					  ovl_layer_lower(this)->fsid,
-					  p->name, p->len);
+					  p->name, p->len,
+					  ovl_xino_warn(dir->d_sb));
 	}
 
 out:
@@ -651,6 +654,7 @@ struct ovl_readdir_translate {
 	u64 parent_ino;
 	int fsid;
 	int xinobits;
+	bool xinowarn;
 };
 
 static int ovl_fill_real(struct dir_context *ctx, const char *name,
@@ -671,7 +675,7 @@ static int ovl_fill_real(struct dir_context *ctx, const char *name,
 			ino = p->ino;
 	} else if (rdt->xinobits) {
 		ino = ovl_remap_lower_ino(ino, rdt->xinobits, rdt->fsid,
-					  name, namelen);
+					  name, namelen, rdt->xinowarn);
 	}
 
 	return orig_ctx->actor(orig_ctx, name, namelen, offset, ino, d_type);
@@ -702,6 +706,7 @@ static int ovl_iterate_real(struct file *file, struct dir_context *ctx)
 		.ctx.actor = ovl_fill_real,
 		.orig_ctx = ctx,
 		.xinobits = ovl_xino_bits(dir->d_sb),
+		.xinowarn = ovl_xino_warn(dir->d_sb),
 	};
 
 	if (rdt.xinobits && lower_layer)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 53dd094f970e..732ad5495c92 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -317,12 +317,6 @@ static const char *ovl_redirect_mode_def(void)
 	return ovl_redirect_dir_def ? "on" : "off";
 }
 
-enum {
-	OVL_XINO_OFF,
-	OVL_XINO_AUTO,
-	OVL_XINO_ON,
-};
-
 static const char * const ovl_xino_str[] = {
 	"off",
 	"auto",
@@ -1479,8 +1473,8 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 
 	/*
 	 * When all layers on same fs, overlay can use real inode numbers.
-	 * With mount option "xino=on", mounter declares that there are enough
-	 * free high bits in underlying fs to hold the unique fsid.
+	 * With mount option "xino=<on|auto>", mounter declares that there are
+	 * enough free high bits in underlying fs to hold the unique fsid.
 	 * If overlayfs does encounter underlying inodes using the high xino
 	 * bits reserved for fsid, it emits a warning and uses the original
 	 * inode number or a non persistent inode number allocated from a
@@ -1492,7 +1486,7 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 		ofs->xino_mode = 0;
 	} else if (ofs->config.xino == OVL_XINO_OFF) {
 		ofs->xino_mode = -1;
-	} else if (ofs->config.xino == OVL_XINO_ON && ofs->xino_mode < 0) {
+	} else if (ofs->xino_mode < 0) {
 		/*
 		 * This is a roundup of number of bits needed for encoding
 		 * fsid, where fsid 0 is reserved for upper fs (even with

From 2eda9eaa6d7ec129150df4c7b7be65f27ac47346 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Fri, 21 Feb 2020 16:34:46 +0200
Subject: [PATCH 20/20] ovl: document xino expected behavior

Summarize the inode properties of different configurations in a table.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 Documentation/filesystems/overlayfs.rst | 38 +++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
index e398fdf7353e..c9d2bf96b02d 100644
--- a/Documentation/filesystems/overlayfs.rst
+++ b/Documentation/filesystems/overlayfs.rst
@@ -40,13 +40,46 @@ On 64bit systems, even if all overlay layers are not on the same
 underlying filesystem, the same compliant behavior could be achieved
 with the "xino" feature.  The "xino" feature composes a unique object
 identifier from the real object st_ino and an underlying fsid index.
+
 If all underlying filesystems support NFS file handles and export file
 handles with 32bit inode number encoding (e.g. ext4), overlay filesystem
 will use the high inode number bits for fsid.  Even when the underlying
 filesystem uses 64bit inode numbers, users can still enable the "xino"
 feature with the "-o xino=on" overlay mount option.  That is useful for the
 case of underlying filesystems like xfs and tmpfs, which use 64bit inode
-numbers, but are very unlikely to use the high inode number bit.
+numbers, but are very unlikely to use the high inode number bits.  In case
+the underlying inode number does overflow into the high xino bits, overlay
+filesystem will fall back to the non xino behavior for that inode.
+
+The following table summarizes what can be expected in different overlay
+configurations.
+
+Inode properties
+````````````````
+
++--------------+------------+------------+-----------------+----------------+
+|Configuration | Persistent | Uniform    | st_ino == d_ino | d_ino == i_ino |
+|              | st_ino     | st_dev     |                 | [*]            |
++==============+=====+======+=====+======+========+========+========+=======+
+|              | dir | !dir | dir | !dir |  dir   +  !dir  |  dir   | !dir  |
++--------------+-----+------+-----+------+--------+--------+--------+-------+
+| All layers   |  Y  |  Y   |  Y  |  Y   |  Y     |   Y    |  Y     |  Y    |
+| on same fs   |     |      |     |      |        |        |        |       |
++--------------+-----+------+-----+------+--------+--------+--------+-------+
+| Layers not   |  N  |  Y   |  Y  |  N   |  N     |   Y    |  N     |  Y    |
+| on same fs,  |     |      |     |      |        |        |        |       |
+| xino=off     |     |      |     |      |        |        |        |       |
++--------------+-----+------+-----+------+--------+--------+--------+-------+
+| xino=on/auto |  Y  |  Y   |  Y  |  Y   |  Y     |   Y    |  Y     |  Y    |
+|              |     |      |     |      |        |        |        |       |
++--------------+-----+------+-----+------+--------+--------+--------+-------+
+| xino=on/auto,|  N  |  Y   |  Y  |  N   |  N     |   Y    |  N     |  Y    |
+| ino overflow |     |      |     |      |        |        |        |       |
++--------------+-----+------+-----+------+--------+--------+--------+-------+
+
+[*] nfsd v3 readdirplus verifies d_ino == i_ino. i_ino is exposed via several
+/proc files, such as /proc/locks and /proc/self/fdinfo/<fd> of an inotify
+file descriptor.
 
 
 Upper and Lower
@@ -427,7 +460,8 @@ guarantee that the values of st_ino and st_dev returned by stat(2) and the
 value of d_ino returned by readdir(3) will act like on a normal filesystem.
 E.g. the value of st_dev may be different for two objects in the same
 overlay filesystem and the value of st_ino for directory objects may not be
-persistent and could change even while the overlay filesystem is mounted.
+persistent and could change even while the overlay filesystem is mounted, as
+summarized in the `Inode properties`_ table above.
 
 
 Changes to underlying filesystems