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authorAmir Goldstein <amir73il@gmail.com>2019-04-18 17:42:08 +0300
committerMiklos Szeredi <mszeredi@redhat.com>2019-05-29 14:03:37 +0300
commit146d62e5a5867fbf84490d82455718bfb10fe824 (patch)
tree60bea762ab581345f62f150f4939f2fa36998dc2 /fs/overlayfs/namei.c
parentb21d9c435f935014d3e3fa6914f2e4fbabb0e94d (diff)
downloadlinux-146d62e5a5867fbf84490d82455718bfb10fe824.tar.xz
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/namei.c')
-rw-r--r--fs/overlayfs/namei.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index efd372312ef1..badf039267a2 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -18,6 +18,7 @@
#include "overlayfs.h"
struct ovl_lookup_data {
+ struct super_block *sb;
struct qstr name;
bool is_dir;
bool opaque;
@@ -244,6 +245,12 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
if (!d->metacopy || d->last)
goto out;
} else {
+ if (ovl_lookup_trap_inode(d->sb, this)) {
+ /* Caught in a trap of overlapping layers */
+ err = -ELOOP;
+ goto out_err;
+ }
+
if (last_element)
d->is_dir = true;
if (d->last)
@@ -819,6 +826,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
int err;
bool metacopy = false;
struct ovl_lookup_data d = {
+ .sb = dentry->d_sb,
.name = dentry->d_name,
.is_dir = false,
.opaque = false,