Fix buffer overflow when processing SCRAM final message in libpq

michaelpq · michaelpq · commit d72a7e4da100 · 2019-06-17T22:14:09.000+09:00
When a client connects to a rogue server sending specifically-crafted messages, this can suffice to execute arbitrary code as the operating system account used by the client. While on it, fix one error handling when decoding an incorrect salt included in the first message received from server. Author: Michael Paquier Reviewed-by: Jonathan Katz, Heikki Linnakangas Security: CVE-2019-10164 Backpatch-through: 10
diff --git a/src/interfaces/libpq/fe-auth-scram.c b/src/interfaces/libpq/fe-auth-scram.c
@@ -462,6 +462,12 @@ read_server_first_message(fe_scram_state *state, char *input,
 	state->saltlen = pg_b64_decode(encoded_salt,
 								   strlen(encoded_salt),
 								   state->salt);
+	if (state->saltlen < 0)
+	{
+		printfPQExpBuffer(errormessage,
+						  libpq_gettext("malformed SCRAM message (invalid salt)\n"));
+		return false;
+	}
 
 	iterations_str = read_attr_value(&input, 'i', errormessage);
 	if (iterations_str == NULL)
@@ -492,6 +498,7 @@ read_server_final_message(fe_scram_state *state, char *input,
 						  PQExpBuffer errormessage)
 {
 	char	   *encoded_server_signature;
+	char	   *decoded_server_signature;
 	int			server_signature_len;
 
 	state->server_final_message = strdup(input);
@@ -525,15 +532,27 @@ read_server_final_message(fe_scram_state *state, char *input,
 		printfPQExpBuffer(errormessage,
 						  libpq_gettext("malformed SCRAM message (garbage at end of server-final-message)\n"));
 
+	server_signature_len = pg_b64_dec_len(strlen(encoded_server_signature));
+	decoded_server_signature = malloc(server_signature_len);
+	if (!decoded_server_signature)
+	{
+		printfPQExpBuffer(errormessage,
+						  libpq_gettext("out of memory\n"));
+		return false;
+	}
+
 	server_signature_len = pg_b64_decode(encoded_server_signature,
 										 strlen(encoded_server_signature),
-										 state->ServerSignature);
+										 decoded_server_signature);
 	if (server_signature_len != SCRAM_KEY_LEN)
 	{
+		free(decoded_server_signature);
 		printfPQExpBuffer(errormessage,
 						  libpq_gettext("malformed SCRAM message (invalid server signature)\n"));
 		return false;
 	}
+	memcpy(state->ServerSignature, decoded_server_signature, SCRAM_KEY_LEN);
+	free(decoded_server_signature);
 
 	return true;
 }
