cifs: allow guest mounts to work for smb3.11

Fix Guest/Anonymous sessions so that they work with SMB 3.11.

The commit noted below tightened the conditions and forced signing for
the SMB2-TreeConnect commands as per MS-SMB2.
However, this should only apply to normal user sessions and not for
Guest/Anonumous sessions.

Fixes: 6188f28b ("Tree connect for SMB3.1.1 must be signed for non-encrypted shares")
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -1628,9 +1628,13 @@ SMB2_tcon(const unsigned int xid, struct cifs_ses *ses, const char *tree,
 	iov[1].iov_base = unc_path;
 	iov[1].iov_len = unc_path_len;
 
-	/* 3.11 tcon req must be signed if not encrypted. See MS-SMB2 3.2.4.1.1 */
+	/*
+	 * 3.11 tcon req must be signed if not encrypted. See MS-SMB2 3.2.4.1.1
+	 * unless it is guest or anonymous user. See MS-SMB2 3.2.5.3.1
+	 */
 	if ((ses->server->dialect == SMB311_PROT_ID) &&
-	    !smb3_encryption_required(tcon))
+	    !smb3_encryption_required(tcon) &&
+	    !(ses->session_flags & (SMB2_SESSION_FLAG_IS_GUEST|SMB2_SESSION_FLAG_IS_NULL)))
 		req->sync_hdr.Flags |= SMB2_FLAGS_SIGNED;
 
 	memset(&rqst, 0, sizeof(struct smb_rqst));