[PATCH 4.19 16/44] ovl: fix missing override creds in link of a metacopy upper

Greg Kroah-Hartman
2018-12-18T16:41:14Z

From: Amir Goldstein <amir73il@gmail.com>

commit 91ff20f34e94424e586f57f4f593beae16504f86 upstream.

Theodore Ts'o reported a v4.19 regression with docker-dropbox:
https://marc.info/?l=linux-fsdevel&m=154070089431116&w=2

"I was rebuilding my dropbox Docker container, and it failed in 4.19
with the following error:
...
dpkg: error: error creating new backup file \
'/var/lib/dpkg/status-old': Invalid cross-device link"

The problem did not reproduce with metacopy feature disabled.
The error was caused by insufficient credentials to set
"trusted.overlay.redirect" xattr on link of a metacopy file.

Reproducer:

echo Y > /sys/module/overlay/parameters/redirect_dir
echo Y > /sys/module/overlay/parameters/metacopy
cd /tmp
mkdir l u w m
chmod 777 l u
touch l/foo
ln l/foo l/link
chmod 666 l/foo
mount -t overlay none -olowerdir=l,upperdir=u,workdir=w m
su fsgqa
ln m/foo m/bar
[ 21.455823] overlayfs: failed to set redirect (-1)
ln: failed to create hard link 'm/bar' => 'm/foo':\
Invalid cross-device link

Reported-by: Theodore Y. Ts'o <tytso@mit.edu>
Reported-by: Maciej Zięba <maciekz82@gmail.com>
Fixes: 4120fe64dce4 ("ovl: Set redirect on upper inode when it is linked")
Cc: <stable@vger.kernel.org> # v4.19
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/overlayfs/dir.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -652,6 +652,18 @@ static int ovl_symlink(struct inode *dir
return ovl_create_object(dentry, S_IFLNK, 0, link);
}

+static int ovl_set_link_redirect(struct dentry *dentry)
+{
+ const struct cred *old_cred;
+ int err;
+
+ old_cred = ovl_override_creds(dentry->d_sb);
+ err = ovl_set_redirect(dentry, false);
+ revert_creds(old_cred);
+
+ return err;
+}
+
static int ovl_link(struct dentry *old, struct inode *newdir,
struct dentry *new)
{
@@ -672,7 +684,7 @@ static int ovl_link(struct dentry *old,
goto out_drop_write;

if (ovl_is_metacopy_dentry(old)) {
- err = ovl_set_redirect(old, false);
+ err = ovl_set_link_redirect(old);
if (err)
goto out_drop_write;
}