ovl: fix uid/gid when creating over whiteout

[ Upstream commit d0e13f5bbe4be7c8f27736fc40503dcec04b7de0 ]

Fix a regression when creating a file over a whiteout.  The new
file/directory needs to use the current fsuid/fsgid, not the ones from the
mounter's credentials.

The refcounting is a bit tricky: prepare_creds() sets an original refcount,
override_creds() gets one more, which revert_cred() drops.  So

  1) we need to expicitly put the mounter's credentials when overriding
     with the updated one

  2) we need to put the original ref to the updated creds (and this can
     safely be done before revert_creds(), since we'll still have the ref
     from override_creds()).

Reported-by: Stephen Smalley <sds@tycho.nsa.gov>
Fixes: 3fe6e52f0626 ("ovl: override creds with the ones from the superblock mounter")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>
[sw0312.kim: cherry-pick linux-4.4.y commit 54a07fff4b21 to fix smack deny issue on overlayfs]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I20e6184091fd96a3fcd9aea8c8026f5532795cd3

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index f8aa542721213281c1f3df0982c649afec2ebf0d..eedacae889b95475a863d4691eded586702c7a43 100644 (file)
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -408,12 +408,21 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev,
                err = ovl_create_upper(dentry, inode, &stat, link, hardlink);
        } else {
                const struct cred *old_cred;
+               struct cred *override_cred;
 
                old_cred = ovl_override_creds(dentry->d_sb);
 
-               err = ovl_create_over_whiteout(dentry, inode, &stat, link,
-                                              hardlink);
+               err = -ENOMEM;
+               override_cred = prepare_creds();
+               if (override_cred) {
+                       override_cred->fsuid = old_cred->fsuid;
+                       override_cred->fsgid = old_cred->fsgid;
+                       put_cred(override_creds(override_cred));
+                       put_cred(override_cred);
 
+                       err = ovl_create_over_whiteout(dentry, inode, &stat,
+                                                      link, hardlink);
+               }
                revert_creds(old_cred);
        }