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authorAmir Goldstein <amir73il@gmail.com>2019-04-18 16:42:08 +0200
committerMiklos Szeredi <mszeredi@redhat.com>2019-05-29 13:03:37 +0200
commit146d62e5a5867fbf84490d82455718bfb10fe824 (patch)
tree60bea762ab581345f62f150f4939f2fa36998dc2 /fs/overlayfs/util.c
parentovl: support the FS_IOC_FS[SG]ETXATTR ioctls (diff)
downloadlinux-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.c12
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?
*/