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

[Vivek Goyal <vgoyal@redhat.com>]

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 <vgoyal@redhat.com>
---
 fs/overlayfs/namei.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index beb945e1963c..ef3e7ea76296 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -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