fs/cifs: correctly to anonymous authentication for the LANMAN authentication

commit fa8f3a35 upstream.

Only server which map unknown users to guest will allow
access using a non-null LMChallengeResponse.

For Samba it's the "map to guest = bad user" option.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11913Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>
[bwh: Backported to 3.16: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/cifs/sess.c

@@ -632,8 +632,8 @@ CIFS_SessSetup(const unsigned int xid, struct cifs_ses *ses,
 
 		pSMB->req.hdr.Flags2 &= ~SMBFLG2_UNICODE;
 
+		if (ses->user_name != NULL) {
 			/* no capabilities flags in old lanman negotiation */
-
 			pSMB->old_req.PasswordLength = cpu_to_le16(CIFS_AUTH_RESP_SIZE);
 
 			/* Calculate hash with password and copy into bcc_ptr.
@@ -641,13 +641,15 @@ CIFS_SessSetup(const unsigned int xid, struct cifs_ses *ses,
 			 * security mode bit in Negottiate Protocol response states
 			 * to use challenge/response method (i.e. Password bit is 1).
 			 */
-
 			rc = calc_lanman_hash(ses->password, ses->server->cryptkey,
 					      ses->server->sec_mode & SECMODE_PW_ENCRYPT ?
 					      true : false, lnm_session_key);
 
 			memcpy(bcc_ptr, (char *)lnm_session_key, CIFS_AUTH_RESP_SIZE);
 			bcc_ptr += CIFS_AUTH_RESP_SIZE;
+		} else {
+			pSMB->old_req.PasswordLength = 0;
+		}
 
 		/* can not sign if LANMAN negotiated so no need
 		to calculate signing key? but what if server