ovl: redirect_dir=nofollow should not follow redirect for opaque lower

redirect_dir=nofollow should not follow a redirect. But in a specific configuration it can still follow it. For example try this.

$ mkdir -p lower0 lower1/foo upper work merged
$ touch lower1/foo/lower-file.txt
$ setfattr -n "trusted.overlay.opaque" -v "y" lower1/foo
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=on none merged
$ cd merged
$ mv foo foo-renamed
$ umount merged

# mount again. This time with redirect_dir=nofollow
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=nofollow none merged
$ ls merged/foo-renamed/
# This lists lower-file.txt, while it should not have.

Basically, we are doing redirect check after we check for d.stop. And if this is not last lower, and we find an opaque lower, d.stop will be set.

ovl_lookup_single()

        if (!d->last && ovl_is_opaquedir(this)) {
                d->stop = d->opaque = true;
                goto out;
        }

To fix this, first check redirect is allowed. And after that check if d.stop has been set or not.

Signed-off-by Vivek Goyal <[email protected]>

---
 fs/overlayfs/namei.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

fs/overlayfs/namei.c +3 -4

index beb945e1963c..ef3e7ea76296 100644
@@ -678,9 +678,6 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                stack[ctr].layer = lower.layer;
                ctr++;
 
-               if (d.stop)
-                       break;
-
                /*
                 * Following redirects can have security consequences: it's like
                 * a symlink into the lower layer without the permission checks.

@@ -697,6 +694,9 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                        goto out_put;
                }
 
+               if (d.stop)
+                       break;
+
                if (d.redirect && d.redirect[0] == '/' && poe != roe) {
                        poe = roe;
 
--

2.13.6

redirect_dir=nofollow should not follow a redirect. But in a specific configuration it can still follow it. For example try this.

$ mkdir -p lower0 lower1/foo upper work merged
$ touch lower1/foo/lower-file.txt
$ setfattr -n "trusted.overlay.opaque" -v "y" lower1/foo
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=on none merged
$ cd merged
$ mv foo foo-renamed
$ umount merged

# mount again. This time with redirect_dir=nofollow
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=nofollow none merged
$ ls merged/foo-renamed/
# This lists lower-file.txt, while it should not have.

Basically, we are doing redirect check after we check for d.stop. And if this is not last lower, and we find an opaque lower, d.stop will be set.

ovl_lookup_single()

        if (!d->last && ovl_is_opaquedir(this)) {
                d->stop = d->opaque = true;
                goto out;
        }

To fix this, first check redirect is allowed. And after that check if d.stop has been set or not.

Signed-off-by Vivek Goyal <[email protected]>

redirect_dir=nofollow should not follow a redirect. But in a specific configuration it can still follow it. For example try this.

$ mkdir -p lower0 lower1/foo upper work merged
$ touch lower1/foo/lower-file.txt
$ setfattr -n "trusted.overlay.opaque" -v "y" lower1/foo
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=on none merged
$ cd merged
$ mv foo foo-renamed
$ umount merged

# mount again. This time with redirect_dir=nofollow
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=nofollow none merged
$ ls merged/foo-renamed/
# This lists lower-file.txt, while it should not have.

Basically, we are doing redirect check after we check for d.stop. And if this is not last lower, and we find an opaque lower, d.stop will be set.

ovl_lookup_single()

        if (!d->last && ovl_is_opaquedir(this)) {
                d->stop = d->opaque = true;
                goto out;
        }

To fix this, first check redirect is allowed. And after that check if d.stop has been set or not.

Signed-off-by Vivek Goyal <[email protected]>

Quoted 26 lines · Vivek Goyal

redirect_dir=nofollow should not follow a redirect. But in a specific configuration it can still follow it. For example try this.

$ mkdir -p lower0 lower1/foo upper work merged
$ touch lower1/foo/lower-file.txt
$ setfattr -n "trusted.overlay.opaque" -v "y" lower1/foo
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=on none merged
$ cd merged
$ mv foo foo-renamed
$ umount merged

# mount again. This time with redirect_dir=nofollow
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=nofollow none merged
$ ls merged/foo-renamed/
# This lists lower-file.txt, while it should not have.

Basically, we are doing redirect check after we check for d.stop. And if this is not last lower, and we find an opaque lower, d.stop will be set.

ovl_lookup_single()

        if (!d->last && ovl_is_opaquedir(this)) {
                d->stop = d->opaque = true;
                goto out;
        }

Quoted 4 lines

To fix this, first check redirect is allowed. And after that check if d.stop has been set or not.

Signed-off-by Vivek Goyal <[email protected]>

This is already in overlayfs-next, which is the branch you should be rebasing on..

Quoted 26 lines · Vivek Goyal

redirect_dir=nofollow should not follow a redirect. But in a specific configuration it can still follow it. For example try this.

$ mkdir -p lower0 lower1/foo upper work merged
$ touch lower1/foo/lower-file.txt
$ setfattr -n "trusted.overlay.opaque" -v "y" lower1/foo
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=on none merged
$ cd merged
$ mv foo foo-renamed
$ umount merged

# mount again. This time with redirect_dir=nofollow
$ mount -t overlay -o lowerdir=lower1:lower0,workdir=work,upperdir=upper,redirect_dir=nofollow none merged
$ ls merged/foo-renamed/
# This lists lower-file.txt, while it should not have.

Basically, we are doing redirect check after we check for d.stop. And if this is not last lower, and we find an opaque lower, d.stop will be set.

ovl_lookup_single()

        if (!d->last && ovl_is_opaquedir(this)) {
                d->stop = d->opaque = true;
                goto out;
        }

Quoted 4 lines

To fix this, first check redirect is allowed. And after that check if d.stop has been set or not.

Signed-off-by Vivek Goyal <[email protected]>

This is already in overlayfs-next, which is the branch you should be rebasing on..