cifs: return correct error in ->calc_signature()

If an error happens while getting the key or session in the
->calc_signature implementations, 0 (success) is returned. Fix it by
returning a proper error code.

Since it seems to be highly unlikely to happen wrap the rc check in
unlikely() too.
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Fixes: 32811d24 ("cifs: Start using per session key for smb2/3 for signature generation")
Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2transport.c

@@ -225,9 +225,9 @@ smb2_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server,
 	struct smb_rqst drqst;
 
 	ses = smb2_find_smb_ses(server, le64_to_cpu(shdr->SessionId));
-	if (!ses) {
+	if (unlikely(!ses)) {
 		cifs_server_dbg(VFS, "%s: Could not find session\n", __func__);
-		return 0;
+		return -ENOENT;
 	}
 
 	memset(smb2_signature, 0x0, SMB2_HMACSHA256_SIZE);
@@ -557,8 +557,10 @@ smb3_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server,
 	u8 key[SMB3_SIGN_KEY_SIZE];
 
 	rc = smb2_get_sign_key(le64_to_cpu(shdr->SessionId), server, key);
-	if (rc)
-		return 0;
+	if (unlikely(rc)) {
+		cifs_server_dbg(VFS, "%s: Could not get signing key\n", __func__);
+		return rc;
+	}
 
 	if (allocate_crypto) {
 		rc = cifs_alloc_hash("cmac(aes)", &hash, &sdesc);