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author | Amir Goldstein <amir73il@gmail.com> | 2019-04-18 16:42:08 +0200 |
---|---|---|
committer | Miklos Szeredi <mszeredi@redhat.com> | 2019-05-29 13:03:37 +0200 |
commit | 146d62e5a5867fbf84490d82455718bfb10fe824 (patch) | |
tree | 60bea762ab581345f62f150f4939f2fa36998dc2 /fs/overlayfs/util.c | |
parent | ovl: support the FS_IOC_FS[SG]ETXATTR ioctls (diff) | |
download | linux-146d62e5a5867fbf84490d82455718bfb10fe824.tar.xz linux-146d62e5a5867fbf84490d82455718bfb10fe824.zip |
ovl: detect overlapping layers
Overlapping overlay layers are not supported and can cause unexpected
behavior, but overlayfs does not currently check or warn about these
configurations.
User is not supposed to specify the same directory for upper and
lower dirs or for different lower layers and user is not supposed to
specify directories that are descendants of each other for overlay
layers, but that is exactly what this zysbot repro did:
https://syzkaller.appspot.com/x/repro.syz?x=12c7a94f400000
Moving layer root directories into other layers while overlayfs
is mounted could also result in unexpected behavior.
This commit places "traps" in the overlay inode hash table.
Those traps are dummy overlay inodes that are hashed by the layers
root inodes.
On mount, the hash table trap entries are used to verify that overlay
layers are not overlapping. While at it, we also verify that overlay
layers are not overlapping with directories "in-use" by other overlay
instances as upperdir/workdir.
On lookup, the trap entries are used to verify that overlay layers
root inodes have not been moved into other layers after mount.
Some examples:
$ ./run --ov --samefs -s
...
( mkdir -p base/upper/0/u base/upper/0/w base/lower lower upper mnt
mount -o bind base/lower lower
mount -o bind base/upper upper
mount -t overlay none mnt ...
-o lowerdir=lower,upperdir=upper/0/u,workdir=upper/0/w)
$ umount mnt
$ mount -t overlay none mnt ...
-o lowerdir=base,upperdir=upper/0/u,workdir=upper/0/w
[ 94.434900] overlayfs: overlapping upperdir path
mount: mount overlay on mnt failed: Too many levels of symbolic links
$ mount -t overlay none mnt ...
-o lowerdir=upper/0/u,upperdir=upper/0/u,workdir=upper/0/w
[ 151.350132] overlayfs: conflicting lowerdir path
mount: none is already mounted or mnt busy
$ mount -t overlay none mnt ...
-o lowerdir=lower:lower/a,upperdir=upper/0/u,workdir=upper/0/w
[ 201.205045] overlayfs: overlapping lowerdir path
mount: mount overlay on mnt failed: Too many levels of symbolic links
$ mount -t overlay none mnt ...
-o lowerdir=lower,upperdir=upper/0/u,workdir=upper/0/w
$ mv base/upper/0/ base/lower/
$ find mnt/0
mnt/0
mnt/0/w
find: 'mnt/0/w/work': Too many levels of symbolic links
find: 'mnt/0/u': Too many levels of symbolic links
Reported-by: syzbot+9c69c282adc4edd2b540@syzkaller.appspotmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/overlayfs/util.c')
-rw-r--r-- | fs/overlayfs/util.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c index 4035e640f402..e135064e87ad 100644 --- a/fs/overlayfs/util.c +++ b/fs/overlayfs/util.c @@ -652,6 +652,18 @@ void ovl_inuse_unlock(struct dentry *dentry) } } +bool ovl_is_inuse(struct dentry *dentry) +{ + struct inode *inode = d_inode(dentry); + bool inuse; + + spin_lock(&inode->i_lock); + inuse = (inode->i_state & I_OVL_INUSE); + spin_unlock(&inode->i_lock); + + return inuse; +} + /* * Does this overlay dentry need to be indexed on copy up? */ |