smb: client: fix dfs link mount against w2k8

Customer reported that they couldn't mount their DFS link that was
seen by the client as a DFS interlink -- special form of DFS link
where its single target may point to a different DFS namespace -- and
it turned out that it was just a regular DFS link where its referral
header flags missed the StorageServers bit thus making the client
think it couldn't tree connect to target directly without requiring
further referrals.

When the DFS link referral header flags misses the StoraServers bit
and its target doesn't respond to any referrals, then tree connect to
it.

Fixes: a1c0d005 ("cifs: share dfs connections and supers")
Cc: stable@vger.kernel.org
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/dfs.c

@@ -177,8 +177,12 @@ static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
 		struct dfs_cache_tgt_list tl = DFS_CACHE_TGT_LIST_INIT(tl);
 
 		rc = dfs_get_referral(mnt_ctx, ref_path + 1, NULL, &tl);
-		if (rc)
+		if (rc) {
+			rc = cifs_mount_get_tcon(mnt_ctx);
+			if (!rc)
+				rc = cifs_is_path_remote(mnt_ctx);
 			break;
+		}
 
 		tit = dfs_cache_get_tgt_iterator(&tl);
 		if (!tit) {