cifs: Do not use the original cruid when following DFS links for multiuser mounts

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=213565

cruid should only be used for the initial mount and after this we should use the current
users credentials.
Ignore the original cruid mount argument when creating a new context for a multiuser mount
following a DFS link.

Fixes: 24e0a1e ("cifs: switch to new mount api")
Cc: stable@vger.kernel.org # 5.11+
Reported-by: Xiaoli Feng <xifeng@redhat.com>
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Ronnie Sahlberg

fs/cifs/cifs_dfs_ref.c

@@ -211,6 +211,10 @@ char *cifs_compose_mount_options(const char *sb_mountdata,
 		else
 			noff = tkn_e - (sb_mountdata + off) + 1;
 
+		if (strncasecmp(sb_mountdata + off, "cruid=", 6) == 0) {
+			off += noff;
+			continue;
+		}
 		if (strncasecmp(sb_mountdata + off, "unc=", 4) == 0) {
 			off += noff;
 			continue;