fs/cifs: correctly to anonymous authentication via NTLMSSP

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

CC: Stable <stable@vger.kernel.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>

diff --git a/fs/cifs/sess.c b/fs/cifs/sess.c
index 59727e32ed0f68871785b17b0df0f41bf9e4f378..09b0201d15d00ca1000ffdf4ef6e21f940181965 100644 (file)
--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -400,19 +400,27 @@ int build_ntlmssp_auth_blob(unsigned char *pbuffer,
        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;
+       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);
+       } else {
+               /*
+                * don't send an NT Response for anonymous access
+                */
+               sec_blob->NtChallengeResponse.Length = 0;
+               sec_blob->NtChallengeResponse.MaximumLength = 0;
        }
-       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);
 
        if (ses->domainName == NULL) {
                sec_blob->DomainName.BufferOffset = cpu_to_le32(tmp - pbuffer);