mnt: Refactor fs_fully_visible into mount_too_revealing

Replace the call of fs_fully_visible in do_new_mount from before the
new superblock is allocated with a call of mount_too_revealing after
the superblock is allocated.   This winds up being a much better location
for maintainability of the code.

The first change this enables is the replacement of FS_USERNS_VISIBLE
with SB_I_USERNS_VISIBLE.  Moving the flag from struct filesystem_type
to sb_iflags on the superblock.

Unfortunately mount_too_revealing fundamentally needs to touch
mnt_flags adding several MNT_LOCKED_XXX flags at the appropriate
times.  If the mnt_flags did not need to be touched the code
could be easily moved into the filesystem specific mount code.

Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2016-06-09 16:06:06 -05:00
parent 695e9df010
commit 8654df4e2a
5 changed files with 32 additions and 17 deletions

View File

@ -2375,7 +2375,7 @@ unlock:
return err;
}
static bool fs_fully_visible(struct file_system_type *fs_type, int *new_mnt_flags);
static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
/*
* create a new mount for userspace and request it to be added into the
@ -2408,12 +2408,6 @@ static int do_new_mount(struct path *path, const char *fstype, int flags,
flags |= MS_NODEV;
mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
}
if (type->fs_flags & FS_USERNS_VISIBLE) {
if (!fs_fully_visible(type, &mnt_flags)) {
put_filesystem(type);
return -EPERM;
}
}
}
mnt = vfs_kern_mount(type, flags, name, data);
@ -2425,6 +2419,11 @@ static int do_new_mount(struct path *path, const char *fstype, int flags,
if (IS_ERR(mnt))
return PTR_ERR(mnt);
if (mount_too_revealing(mnt, &mnt_flags)) {
mntput(mnt);
return -EPERM;
}
err = do_add_mount(real_mount(mnt), path, mnt_flags);
if (err)
mntput(mnt);
@ -3216,22 +3215,19 @@ bool current_chrooted(void)
return chrooted;
}
static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
int *new_mnt_flags)
{
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
int new_flags = *new_mnt_flags;
struct mount *mnt;
bool visible = false;
if (unlikely(!ns))
return false;
down_read(&namespace_sem);
list_for_each_entry(mnt, &ns->list, mnt_list) {
struct mount *child;
int mnt_flags;
if (mnt->mnt.mnt_sb->s_type != type)
if (mnt->mnt.mnt_sb->s_type != new->mnt_sb->s_type)
continue;
/* This mount is not fully visible if it's root directory
@ -3298,6 +3294,22 @@ found:
return visible;
}
static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
{
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
unsigned long s_iflags;
if (ns->user_ns == &init_user_ns)
return false;
/* Can this filesystem be too revealing? */
s_iflags = mnt->mnt_sb->s_iflags;
if (!(s_iflags & SB_I_USERNS_VISIBLE))
return false;
return !mnt_already_visible(ns, mnt, new_mnt_flags);
}
static struct ns_common *mntns_get(struct task_struct *task)
{
struct ns_common *ns = NULL;

View File

@ -462,6 +462,7 @@ int proc_fill_super(struct super_block *s)
struct inode *root_inode;
int ret;
s->s_iflags |= SB_I_USERNS_VISIBLE;
s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;
s->s_blocksize = 1024;
s->s_blocksize_bits = 10;

View File

@ -158,7 +158,7 @@ static struct file_system_type proc_fs_type = {
.name = "proc",
.mount = proc_mount,
.kill_sb = proc_kill_sb,
.fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
.fs_flags = FS_USERNS_MOUNT,
};
void __init proc_root_init(void)

View File

@ -42,7 +42,7 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
else if (new_sb)
/* Userspace would break if executables appear on sysfs */
root->d_sb->s_iflags |= SB_I_NOEXEC;
root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC;
return root;
}
@ -59,7 +59,7 @@ static struct file_system_type sysfs_fs_type = {
.name = "sysfs",
.mount = sysfs_mount,
.kill_sb = sysfs_kill_sb,
.fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
.fs_flags = FS_USERNS_MOUNT,
};
int __init sysfs_init(void)

View File

@ -1328,6 +1328,9 @@ struct mm_struct;
#define SB_I_CGROUPWB 0x00000001 /* cgroup-aware writeback enabled */
#define SB_I_NOEXEC 0x00000002 /* Ignore executables on this fs */
/* sb->s_iflags to limit user namespace mounts */
#define SB_I_USERNS_VISIBLE 0x00000010 /* fstype already mounted */
/* Possible states of 'frozen' field */
enum {
SB_UNFROZEN = 0, /* FS is unfrozen */
@ -2011,7 +2014,6 @@ struct file_system_type {
#define FS_HAS_SUBTYPE 4
#define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
#define FS_USERNS_DEV_MOUNT 16 /* A userns mount does not imply MNT_NODEV */
#define FS_USERNS_VISIBLE 32 /* FS must already be visible */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
struct dentry *(*mount) (struct file_system_type *, int,
const char *, void *);