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xattr: simple_xattr_set() return old_xattr to be freed 

tmpfs wants to support limited user extended attributes, but kernfs
(or cgroupfs, the only kernfs with KERNFS_ROOT_SUPPORT_USER_XATTR)
already supports user extended attributes through simple xattrs: but
limited by a policy (128KiB per inode) too liberal to be used on tmpfs.

To allow a different limiting policy for tmpfs, without affecting the
policy for kernfs, change simple_xattr_set() to return the replaced or
removed xattr (if any), leaving the caller to update their accounting
then free the xattr (by simple_xattr_free(), renamed from the static
free_simple_xattr()).

Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Message-Id: <158c6585-2aa7-d4aa-90ff-f7c3f8fe407c@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Hugh Dickins 2023-08-08 21:30:59 -07:00 committed by Christian Brauner
parent 0200679fc7
commit 5de75970c9
4 changed files with 61 additions and 53 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

46
fs/kernfs/inode.c
View File

@ -306,11 +306,17 @@ int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
const void *value, size_t size, int flags)
{
struct simple_xattr *old_xattr;
struct kernfs_iattrs *attrs = kernfs_iattrs(kn);
if (!attrs)
return -ENOMEM;
return simple_xattr_set(&attrs->xattrs, name, value, size, flags, NULL);
old_xattr = simple_xattr_set(&attrs->xattrs, name, value, size, flags);
if (IS_ERR(old_xattr))
return PTR_ERR(old_xattr);
simple_xattr_free(old_xattr);
return 0;
}
static int kernfs_vfs_xattr_get(const struct xattr_handler *handler,
@ -342,7 +348,7 @@ static int kernfs_vfs_user_xattr_add(struct kernfs_node *kn,
{
atomic_t *sz = &kn->iattr->user_xattr_size;
atomic_t *nr = &kn->iattr->nr_user_xattrs;
ssize_t removed_size;
struct simple_xattr *old_xattr;
int ret;
if (atomic_inc_return(nr) > KERNFS_MAX_USER_XATTRS) {
@ -355,13 +361,18 @@ static int kernfs_vfs_user_xattr_add(struct kernfs_node *kn,
goto dec_size_out;
}
ret = simple_xattr_set(xattrs, full_name, value, size, flags,
&removed_size);
if (!ret && removed_size >= 0)
size = removed_size;
else if (!ret)
old_xattr = simple_xattr_set(xattrs, full_name, value, size, flags);
if (!old_xattr)
return 0;
if (IS_ERR(old_xattr)) {
ret = PTR_ERR(old_xattr);
goto dec_size_out;
}
ret = 0;
size = old_xattr->size;
simple_xattr_free(old_xattr);
dec_size_out:
atomic_sub(size, sz);
dec_count_out:
@ -376,18 +387,19 @@ static int kernfs_vfs_user_xattr_rm(struct kernfs_node *kn,
{
atomic_t *sz = &kn->iattr->user_xattr_size;
atomic_t *nr = &kn->iattr->nr_user_xattrs;
ssize_t removed_size;
int ret;
struct simple_xattr *old_xattr;
ret = simple_xattr_set(xattrs, full_name, value, size, flags,
&removed_size);
old_xattr = simple_xattr_set(xattrs, full_name, value, size, flags);
if (!old_xattr)
return 0;
if (removed_size >= 0) {
atomic_sub(removed_size, sz);
atomic_dec(nr);
}
if (IS_ERR(old_xattr))
return PTR_ERR(old_xattr);
return ret;
atomic_sub(old_xattr->size, sz);
atomic_dec(nr);
simple_xattr_free(old_xattr);
return 0;
}
static int kernfs_vfs_user_xattr_set(const struct xattr_handler *handler,

51
fs/xattr.c
View File

@ -1040,12 +1040,12 @@ const char *xattr_full_name(const struct xattr_handler *handler,
EXPORT_SYMBOL(xattr_full_name);
/**
* free_simple_xattr - free an xattr object
* simple_xattr_free - free an xattr object
* @xattr: the xattr object
*
* Free the xattr object. Can handle @xattr being NULL.
*/
static inline void free_simple_xattr(struct simple_xattr *xattr)
void simple_xattr_free(struct simple_xattr *xattr)
{
if (xattr)
kfree(xattr->name);
@ -1164,7 +1164,6 @@ int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
* @value: the value to store along the xattr
* @size: the size of @value
* @flags: the flags determining how to set the xattr
* @removed_size: the size of the removed xattr
*
* Set a new xattr object.
* If @value is passed a new xattr object will be allocated. If XATTR_REPLACE
@ -1181,29 +1180,27 @@ int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
* nothing if XATTR_CREATE is specified in @flags or @flags is zero. For
* XATTR_REPLACE we fail as mentioned above.
*
* Return: On success zero and on error a negative error code is returned.
* Return: On success, the removed or replaced xattr is returned, to be freed
* by the caller; or NULL if none. On failure a negative error code is returned.
*/
int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
const void *value, size_t size, int flags,
ssize_t *removed_size)
struct simple_xattr *simple_xattr_set(struct simple_xattrs *xattrs,
const char *name, const void *value,
size_t size, int flags)
{
struct simple_xattr *xattr = NULL, *new_xattr = NULL;
struct simple_xattr *old_xattr = NULL, *new_xattr = NULL;
struct rb_node *parent = NULL, **rbp;
int err = 0, ret;
if (removed_size)
*removed_size = -1;
/* value == NULL means remove */
if (value) {
new_xattr = simple_xattr_alloc(value, size);
if (!new_xattr)
return -ENOMEM;
return ERR_PTR(-ENOMEM);
new_xattr->name = kstrdup(name, GFP_KERNEL);
if (!new_xattr->name) {
free_simple_xattr(new_xattr);
return -ENOMEM;
simple_xattr_free(new_xattr);
return ERR_PTR(-ENOMEM);
}
}
@ -1217,12 +1214,12 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
else if (ret > 0)
rbp = &(*rbp)->rb_right;
else
xattr = rb_entry(*rbp, struct simple_xattr, rb_node);
if (xattr)
old_xattr = rb_entry(*rbp, struct simple_xattr, rb_node);
if (old_xattr)
break;
}
if (xattr) {
if (old_xattr) {
/* Fail if XATTR_CREATE is requested and the xattr exists. */
if (flags & XATTR_CREATE) {
err = -EEXIST;
@ -1230,12 +1227,10 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
}
if (new_xattr)
rb_replace_node(&xattr->rb_node, &new_xattr->rb_node,
&xattrs->rb_root);
rb_replace_node(&old_xattr->rb_node,
&new_xattr->rb_node, &xattrs->rb_root);
else
rb_erase(&xattr->rb_node, &xattrs->rb_root);
if (!err && removed_size)
*removed_size = xattr->size;
rb_erase(&old_xattr->rb_node, &xattrs->rb_root);
} else {
/* Fail if XATTR_REPLACE is requested but no xattr is found. */
if (flags & XATTR_REPLACE) {
@ -1260,12 +1255,10 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
out_unlock:
write_unlock(&xattrs->lock);
if (err)
free_simple_xattr(new_xattr);
else
free_simple_xattr(xattr);
return err;
if (!err)
return old_xattr;
simple_xattr_free(new_xattr);
return ERR_PTR(err);
}
static bool xattr_is_trusted(const char *name)
@ -1386,7 +1379,7 @@ void simple_xattrs_free(struct simple_xattrs *xattrs)
rbp_next = rb_next(rbp);
xattr = rb_entry(rbp, struct simple_xattr, rb_node);
rb_erase(&xattr->rb_node, &xattrs->rb_root);
free_simple_xattr(xattr);
simple_xattr_free(xattr);
rbp = rbp_next;
}
}

7
include/linux/xattr.h
View File

@ -116,11 +116,12 @@ struct simple_xattr {
void simple_xattrs_init(struct simple_xattrs *xattrs);
void simple_xattrs_free(struct simple_xattrs *xattrs);
struct simple_xattr *simple_xattr_alloc(const void *value, size_t size);
void simple_xattr_free(struct simple_xattr *xattr);
int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
void *buffer, size_t size);
int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
const void *value, size_t size, int flags,
ssize_t *removed_size);
struct simple_xattr *simple_xattr_set(struct simple_xattrs *xattrs,
const char *name, const void *value,
size_t size, int flags);
ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
char *buffer, size_t size);
void simple_xattr_add(struct simple_xattrs *xattrs,

10
mm/shmem.c
View File

@ -3598,15 +3598,17 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
size_t size, int flags)
{
struct shmem_inode_info *info = SHMEM_I(inode);
int err;
struct simple_xattr *old_xattr;
name = xattr_full_name(handler, name);
err = simple_xattr_set(&info->xattrs, name, value, size, flags, NULL);
if (!err) {
old_xattr = simple_xattr_set(&info->xattrs, name, value, size, flags);
if (!IS_ERR(old_xattr)) {
simple_xattr_free(old_xattr);
old_xattr = NULL;
inode->i_ctime = current_time(inode);
inode_inc_iversion(inode);
}
return err;
return PTR_ERR(old_xattr);
}
static const struct xattr_handler shmem_security_xattr_handler = {