[PATCH 4.4 14/86] fs/cifs: correctly to anonymous authentication via NTLMSSP

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stefan Metzmacher <metze@xxxxxxxxx>

commit cfda35d98298131bf38fbad3ce4cd5ecb3cf18db upstream.

See [MS-NLMP] 3.2.5.1.2 Server Receives an AUTHENTICATE_MESSAGE from the Client:

   ...
   Set NullSession to FALSE
   If (AUTHENTICATE_MESSAGE.UserNameLen == 0 AND
      AUTHENTICATE_MESSAGE.NtChallengeResponse.Length == 0 AND
      (AUTHENTICATE_MESSAGE.LmChallengeResponse == Z(1)
       OR
       AUTHENTICATE_MESSAGE.LmChallengeResponse.Length == 0))
       -- Special case: client requested anonymous authentication
       Set NullSession to TRUE
   ...

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

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

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11913

Signed-off-by: Stefan Metzmacher <metze@xxxxxxxxx>
Signed-off-by: Steve French <smfrench@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/cifs/sess.c |   32 ++++++++++++++++++++------------
 1 file changed, 20 insertions(+), 12 deletions(-)

--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -400,19 +400,27 @@ int build_ntlmssp_auth_blob(unsigned cha
 	sec_blob->LmChallengeResponse.MaximumLength = 0;
 
 	sec_blob->NtChallengeResponse.BufferOffset = cpu_to_le32(tmp - pbuffer);
-	rc = setup_ntlmv2_rsp(ses, nls_cp);
-	if (rc) {
-		cifs_dbg(VFS, "Error %d during NTLMSSP authentication\n", rc);
-		goto setup_ntlmv2_ret;
-	}
-	memcpy(tmp, ses->auth_key.response + CIFS_SESS_KEY_SIZE,
-			ses->auth_key.len - CIFS_SESS_KEY_SIZE);
-	tmp += ses->auth_key.len - CIFS_SESS_KEY_SIZE;
+	if (ses->user_name != NULL) {
+		rc = setup_ntlmv2_rsp(ses, nls_cp);
+		if (rc) {
+			cifs_dbg(VFS, "Error %d during NTLMSSP authentication\n", rc);
+			goto setup_ntlmv2_ret;
+		}
+		memcpy(tmp, ses->auth_key.response + CIFS_SESS_KEY_SIZE,
+				ses->auth_key.len - CIFS_SESS_KEY_SIZE);
+		tmp += ses->auth_key.len - CIFS_SESS_KEY_SIZE;
 
-	sec_blob->NtChallengeResponse.Length =
-			cpu_to_le16(ses->auth_key.len - CIFS_SESS_KEY_SIZE);
-	sec_blob->NtChallengeResponse.MaximumLength =
-			cpu_to_le16(ses->auth_key.len - CIFS_SESS_KEY_SIZE);
+		sec_blob->NtChallengeResponse.Length =
+				cpu_to_le16(ses->auth_key.len - CIFS_SESS_KEY_SIZE);
+		sec_blob->NtChallengeResponse.MaximumLength =
+				cpu_to_le16(ses->auth_key.len - CIFS_SESS_KEY_SIZE);
+	} else {
+		/*
+		 * don't send an NT Response for anonymous access
+		 */
+		sec_blob->NtChallengeResponse.Length = 0;
+		sec_blob->NtChallengeResponse.MaximumLength = 0;
+	}
 
 	if (ses->domainName == NULL) {
 		sec_blob->DomainName.BufferOffset = cpu_to_le32(tmp - pbuffer);