cifs: fix ntlmssp auth when there is no key exchange

Warn on the lack of key exchange during NTLMSSP authentication rather
than aborting it as there are some servers that do not set it in
CHALLENGE message.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Paulo Alcantara

fs/cifs/sess.c

@@ -590,8 +590,8 @@ int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
 {
 	unsigned int tioffset; /* challenge message target info area */
 	unsigned int tilen; /* challenge message target info area length  */
-
 	CHALLENGE_MESSAGE *pblob = (CHALLENGE_MESSAGE *)bcc_ptr;
+	__u32 server_flags;
 
 	if (blob_len < sizeof(CHALLENGE_MESSAGE)) {
 		cifs_dbg(VFS, "challenge blob len %d too small\n", blob_len);
@@ -609,12 +609,37 @@ int decode_ntlmssp_challenge(char *bcc_ptr, int blob_len,
 		return -EINVAL;
 	}
 
+	server_flags = le32_to_cpu(pblob->NegotiateFlags);
+	cifs_dbg(FYI, "%s: negotiate=0x%08x challenge=0x%08x\n", __func__,
+		 ses->ntlmssp->client_flags, server_flags);
+
+	if ((ses->ntlmssp->client_flags & (NTLMSSP_NEGOTIATE_SEAL | NTLMSSP_NEGOTIATE_SIGN)) &&
+	    (!(server_flags & NTLMSSP_NEGOTIATE_56) && !(server_flags & NTLMSSP_NEGOTIATE_128))) {
+		cifs_dbg(VFS, "%s: requested signing/encryption but server did not return either 56-bit or 128-bit session key size\n",
+			 __func__);
+		return -EINVAL;
+	}
+	if (!(server_flags & NTLMSSP_NEGOTIATE_NTLM) && !(server_flags & NTLMSSP_NEGOTIATE_EXTENDED_SEC)) {
+		cifs_dbg(VFS, "%s: server does not seem to support either NTLMv1 or NTLMv2\n", __func__);
+		return -EINVAL;
+	}
+	if (ses->server->sign && !(server_flags & NTLMSSP_NEGOTIATE_SIGN)) {
+		cifs_dbg(VFS, "%s: forced packet signing but server does not seem to support it\n",
+			 __func__);
+		return -EOPNOTSUPP;
+	}
+	if ((ses->ntlmssp->client_flags & NTLMSSP_NEGOTIATE_KEY_XCH) &&
+	    !(server_flags & NTLMSSP_NEGOTIATE_KEY_XCH))
+		pr_warn_once("%s: authentication has been weakened as server does not support key exchange\n",
+			     __func__);
+
+	ses->ntlmssp->server_flags = server_flags;
+
 	memcpy(ses->ntlmssp->cryptkey, pblob->Challenge, CIFS_CRYPTO_KEY_SIZE);
-	/* BB we could decode pblob->NegotiateFlags; some may be useful */
 	/* In particular we can examine sign flags */
 	/* BB spec says that if AvId field of MsvAvTimestamp is populated then
 		we must set the MIC field of the AUTHENTICATE_MESSAGE */
-	ses->ntlmssp->server_flags = le32_to_cpu(pblob->NegotiateFlags);
+
 	tioffset = le32_to_cpu(pblob->TargetInfoArray.BufferOffset);
 	tilen = le16_to_cpu(pblob->TargetInfoArray.Length);
 	if (tioffset > blob_len || tioffset + tilen > blob_len) {
@@ -721,13 +746,13 @@ int build_ntlmssp_negotiate_blob(unsigned char **pbuffer,
 	flags = NTLMSSP_NEGOTIATE_56 |	NTLMSSP_REQUEST_TARGET |
 		NTLMSSP_NEGOTIATE_128 | NTLMSSP_NEGOTIATE_UNICODE |
 		NTLMSSP_NEGOTIATE_NTLM | NTLMSSP_NEGOTIATE_EXTENDED_SEC |
-		NTLMSSP_NEGOTIATE_SEAL;
-	if (server->sign)
-		flags |= NTLMSSP_NEGOTIATE_SIGN;
+		NTLMSSP_NEGOTIATE_ALWAYS_SIGN | NTLMSSP_NEGOTIATE_SEAL |
+		NTLMSSP_NEGOTIATE_SIGN;
 	if (!server->session_estab || ses->ntlmssp->sesskey_per_smbsess)
 		flags |= NTLMSSP_NEGOTIATE_KEY_XCH;
 
 	tmp = *pbuffer + sizeof(NEGOTIATE_MESSAGE);
+	ses->ntlmssp->client_flags = flags;
 	sec_blob->NegotiateFlags = cpu_to_le32(flags);
 
 	/* these fields should be null in negotiate phase MS-NLMP 3.1.5.1.1 */
@@ -779,15 +804,8 @@ int build_ntlmssp_auth_blob(unsigned char **pbuffer,
 	memcpy(sec_blob->Signature, NTLMSSP_SIGNATURE, 8);
 	sec_blob->MessageType = NtLmAuthenticate;
 
-	flags = NTLMSSP_NEGOTIATE_56 |
-		NTLMSSP_REQUEST_TARGET | NTLMSSP_NEGOTIATE_TARGET_INFO |
-		NTLMSSP_NEGOTIATE_128 | NTLMSSP_NEGOTIATE_UNICODE |
-		NTLMSSP_NEGOTIATE_NTLM | NTLMSSP_NEGOTIATE_EXTENDED_SEC |
-		NTLMSSP_NEGOTIATE_SEAL | NTLMSSP_NEGOTIATE_WORKSTATION_SUPPLIED;
-	if (ses->server->sign)
-		flags |= NTLMSSP_NEGOTIATE_SIGN;
-	if (!ses->server->session_estab || ses->ntlmssp->sesskey_per_smbsess)
-		flags |= NTLMSSP_NEGOTIATE_KEY_XCH;
+	flags = ses->ntlmssp->server_flags | NTLMSSP_REQUEST_TARGET |
+		NTLMSSP_NEGOTIATE_TARGET_INFO | NTLMSSP_NEGOTIATE_WORKSTATION_SUPPLIED;
 
 	tmp = *pbuffer + sizeof(AUTHENTICATE_MESSAGE);
 	sec_blob->NegotiateFlags = cpu_to_le32(flags);
@@ -834,9 +852,9 @@ int build_ntlmssp_auth_blob(unsigned char **pbuffer,
 				      *pbuffer, &tmp,
 				      nls_cp);
 
-	if (((ses->ntlmssp->server_flags & NTLMSSP_NEGOTIATE_KEY_XCH) ||
-		(ses->ntlmssp->server_flags & NTLMSSP_NEGOTIATE_EXTENDED_SEC))
-			&& !calc_seckey(ses)) {
+	if ((ses->ntlmssp->server_flags & NTLMSSP_NEGOTIATE_KEY_XCH) &&
+	    (!ses->server->session_estab || ses->ntlmssp->sesskey_per_smbsess) &&
+	    !calc_seckey(ses)) {
 		memcpy(tmp, ses->ntlmssp->ciphertext, CIFS_CPHTXT_SIZE);
 		sec_blob->SessionKey.BufferOffset = cpu_to_le32(tmp - *pbuffer);
 		sec_blob->SessionKey.Length = cpu_to_le16(CIFS_CPHTXT_SIZE);