On 08/28/2018 11:42 AM, Amir Goldstein wrote:

On Tue, Aug 28, 2018 at 8:43 PM Amir Goldstein [off-list ref] wrote:

quoted

On Tue, Aug 28, 2018 at 7:53 PM Mark Salyzyn [off-list ref] wrote:

quoted

Assumption never checked, should fail if the mounter creds are not
sufficient.

Signed-off-by: Mark Salyzyn <redacted>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric W. Biederman <redacted>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Randy Dunlap <redacted>
Cc: Stephen Smalley <redacted>
Cc: linux-unionfs@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

v5
- dependency of "overlayfs: override_creds=off option bypass creator_cred"
---
  fs/overlayfs/overlayfs.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 7538b9b56237..bf3a80157d42 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h

@@ -176,7 +176,7 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,

  static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
  {
-       int err = vfs_whiteout(dir, dentry);
+       int err = capable(CAP_MKNOD) ? vfs_whiteout(dir, dentry) : -EPERM;

Should that be ns_capable()? Should the test go into vfs_whiteout()?
I feel there is no convention at all.

Nevermind, I don't think creating a whiteout poses any risk, so don't think
we need to worry about CAP_MKNOD.

Thanks,
Amir.

Ok, will discard from the set, we can address this later if it creates 
concern (as in, not a dependency to my proposed feature flag). So we 
feel that whiteout node in the writeable playground of workdir/upperdir 
is not in itself a security concern. Other (more dangerous) mknod will 
be checked against the caller's credentials coming in.

-- Mark