Don't allow immediate interrupts during authentication anymore.

We used to handle authentication_timeout by setting
ImmediateInterruptOK to true during large parts of the authentication
phase of a new connection.  While that happens to work acceptably in
practice, it's not particularly nice and has ugly corner cases.

Previous commits converted the FE/BE communication to use latches and
implemented support for interrupt handling during both
send/recv. Building on top of that work we can get rid of
ImmediateInterruptOK during authentication, by immediately treating
timeouts during authentication as a reason to die. As die interrupts
are handled immediately during client communication that provides a
sensibly quick reaction time to authentication timeout.

Additionally add a few CHECK_FOR_INTERRUPTS() to some more complex
authentication methods. More could be added, but this already should
provides a reasonable coverage.

While it this overall increases the maximum time till a timeout is
reacted to, it greatly reduces complexity and increases
reliability. That seems like a overall win. If the increase proves to
be noticeable we can deal with those cases by moving to nonblocking
network code and add interrupt checking there.

Reviewed-By: Heikki Linnakangas

src/backend/libpq/auth.c

@@ -306,13 +306,6 @@ ClientAuthentication(Port *port)
 	 */
 	hba_getauthmethod(port);
 
-	/*
-	 * Enable immediate response to SIGTERM/SIGINT/timeout interrupts. (We
-	 * don't want this during hba_getauthmethod() because it might have to do
-	 * database access, eg for role membership checks.)
-	 */
-	ImmediateInterruptOK = true;
-	/* And don't forget to detect one that already arrived */
 	CHECK_FOR_INTERRUPTS();
 
 	/*
@@ -566,9 +559,6 @@ ClientAuthentication(Port *port)
 		sendAuthRequest(port, AUTH_REQ_OK);
 	else
 		auth_failed(port, status, logdetail);
-
-	/* Done with authentication, so we should turn off immediate interrupts */
-	ImmediateInterruptOK = false;
 }
 
 
@@ -580,6 +570,8 @@ sendAuthRequest(Port *port, AuthRequest areq)
 {
 	StringInfoData buf;
 
+	CHECK_FOR_INTERRUPTS();
+
 	pq_beginmessage(&buf, 'R');
 	pq_sendint(&buf, (int32) areq, sizeof(int32));
 
@@ -613,6 +605,8 @@ sendAuthRequest(Port *port, AuthRequest areq)
 	 */
 	if (areq != AUTH_REQ_OK)
 		pq_flush();
+
+	CHECK_FOR_INTERRUPTS();
 }
 
 /*
@@ -851,6 +845,9 @@ pg_GSS_recvauth(Port *port)
 	do
 	{
 		pq_startmsgread();
+
+		CHECK_FOR_INTERRUPTS();
+
 		mtype = pq_getbyte();
 		if (mtype != 'p')
 		{
@@ -900,6 +897,8 @@ pg_GSS_recvauth(Port *port)
 			 maj_stat, min_stat,
 			 (unsigned int) port->gss->outbuf.length, gflags);
 
+		CHECK_FOR_INTERRUPTS();
+
 		if (port->gss->outbuf.length != 0)
 		{
 			/*
@@ -1396,6 +1395,9 @@ interpret_ident_response(const char *ident_response,
  *	IP addresses and port numbers are in network byte order.
  *
  *	But iff we're unable to get the information from ident, return false.
+ *
+ *	XXX: Using WaitLatchOrSocket() and doing a CHECK_FOR_INTERRUPTS() if the
+ *	latch was set would improve the responsiveness to timeouts/cancellations.
  */
 static int
 ident_inet(hbaPort *port)
@@ -1510,6 +1512,8 @@ ident_inet(hbaPort *port)
 	/* loop in case send is interrupted */
 	do
 	{
+		CHECK_FOR_INTERRUPTS();
+
 		rc = send(sock_fd, ident_query, strlen(ident_query), 0);
 	} while (rc < 0 && errno == EINTR);
 
@@ -1525,6 +1529,8 @@ ident_inet(hbaPort *port)
 
 	do
 	{
+		CHECK_FOR_INTERRUPTS();
+
 		rc = recv(sock_fd, ident_response, sizeof(ident_response) - 1, 0);
 	} while (rc < 0 && errno == EINTR);
 
@@ -2413,6 +2419,10 @@ CheckRADIUSAuth(Port *port)
 	 * call to select() with a timeout, since somebody can be sending invalid
 	 * packets to our port thus causing us to retry in a loop and never time
 	 * out.
+	 *
+	 * XXX: Using WaitLatchOrSocket() and doing a CHECK_FOR_INTERRUPTS() if
+	 * the latch was set would improve the responsiveness to
+	 * timeouts/cancellations.
 	 */
 	gettimeofday(&endtime, NULL);
 	endtime.tv_sec += RADIUS_TIMEOUT;

src/backend/libpq/be-secure-openssl.c

@@ -377,6 +377,11 @@ aloop:
 				/* not allowed during connection establishment */
 				Assert(!port->noblock);
 
+				/*
+				 * No need to care about timeouts/interrupts here. At this
+				 * point authentication_timeout still employs
+				 * StartupPacketTimeoutHandler() which directly exits.
+				 */
 				if (err == SSL_ERROR_WANT_READ)
 					waitfor = WL_SOCKET_READABLE;
 				else

src/backend/libpq/crypt.c

@@ -47,13 +47,6 @@ md5_crypt_verify(const Port *port, const char *role, char *client_pass,
 	Datum		datum;
 	bool		isnull;
 
-	/*
-	 * Disable immediate interrupts while doing database access.  (Note we
-	 * don't bother to turn this back on if we hit one of the failure
-	 * conditions, since we can expect we'll just exit right away anyway.)
-	 */
-	ImmediateInterruptOK = false;
-
 	/* Get role info from pg_authid */
 	roleTup = SearchSysCache1(AUTHNAME, PointerGetDatum(role));
 	if (!HeapTupleIsValid(roleTup))
@@ -80,9 +73,6 @@ md5_crypt_verify(const Port *port, const char *role, char *client_pass,
 	if (*shadow_pass == '\0')
 		return STATUS_ERROR;	/* empty password */
 
-	/* Re-enable immediate response to SIGTERM/SIGINT/timeout interrupts */
-	ImmediateInterruptOK = true;
-	/* And don't forget to detect one that already arrived */
 	CHECK_FOR_INTERRUPTS();
 
 	/*

src/backend/tcop/postgres.c

@@ -2880,7 +2880,11 @@ ProcessInterrupts(void)
 		/* As in quickdie, don't risk sending to client during auth */
 		if (ClientAuthInProgress && whereToSendOutput == DestRemote)
 			whereToSendOutput = DestNone;
-		if (IsAutoVacuumWorkerProcess())
+		if (ClientAuthInProgress)
+			ereport(FATAL,
+					(errcode(ERRCODE_QUERY_CANCELED),
+					 errmsg("canceling authentication due to timeout")));
+		else if (IsAutoVacuumWorkerProcess())
 			ereport(FATAL,
 					(errcode(ERRCODE_ADMIN_SHUTDOWN),
 					 errmsg("terminating autovacuum process due to administrator command")));
@@ -2959,17 +2963,6 @@ ProcessInterrupts(void)
 		}
 
 		QueryCancelPending = false;
-		if (ClientAuthInProgress)
-		{
-			ImmediateInterruptOK = false;		/* not idle anymore */
-			LockErrorCleanup();
-			/* As in quickdie, don't risk sending to client during auth */
-			if (whereToSendOutput == DestRemote)
-				whereToSendOutput = DestNone;
-			ereport(ERROR,
-					(errcode(ERRCODE_QUERY_CANCELED),
-					 errmsg("canceling authentication due to timeout")));
-		}
 
 		/*
 		 * If LOCK_TIMEOUT and STATEMENT_TIMEOUT indicators are both set, we

src/backend/utils/init/postinit.c

@@ -1099,18 +1099,24 @@ ShutdownPostgres(int code, Datum arg)
 static void
 StatementTimeoutHandler(void)
 {
+	int sig = SIGINT;
+
+	/*
+	 * During authentication the timeout is used to deal with
+	 * authentication_timeout - we want to quit in response to such timeouts.
+	 */
+	if (ClientAuthInProgress)
+		sig = SIGTERM;
+
 #ifdef HAVE_SETSID
 	/* try to signal whole process group */
-	kill(-MyProcPid, SIGINT);
+	kill(-MyProcPid, sig);
 #endif
-	kill(MyProcPid, SIGINT);
+	kill(MyProcPid, sig);
 }
 
 /*
  * LOCK_TIMEOUT handler: trigger a query-cancel interrupt.
- *
- * This is identical to StatementTimeoutHandler, but since it's so short,
- * we might as well keep the two functions separate for clarity.
  */
 static void
 LockTimeoutHandler(void)