Avoid extra system calls to block SIGPIPE if the platform provides either

tglsfdc · tglsfdc · commit cea80e726edd · 2009-07-24T17:58:31.000Z
sockopt(SO_NOSIGPIPE) or the MSG_NOSIGNAL flag to send().

We assume these features are available if (1) the symbol is defined at
compile time and (2) the kernel doesn't reject the call at runtime.
It might turn out that there are some platforms where (1) and (2) are
true and yet the signal isn't really blocked, in which case applications
would die on server crash.  If that sort of thing gets reported, then
we'll have to add additional defenses of some kind.

Jeremy Kerr
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-connect.c,v 1.375 2009/06/11 14:49:13 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-connect.c,v 1.376 2009/07/24 17:58:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1018,6 +1018,7 @@ PQconnectPoll(PGconn *conn)
 {
 	PGresult   *res;
 	char		sebuf[256];
+	int			optval;
 
 	if (conn == NULL)
 		return PGRES_POLLING_FAILED;
@@ -1153,6 +1154,46 @@ PQconnectPoll(PGconn *conn)
 					}
 #endif   /* F_SETFD */
 
+					/*----------
+					 * We have three methods of blocking SIGPIPE during
+					 * send() calls to this socket:
+					 *
+					 *  - setsockopt(sock, SO_NOSIGPIPE)
+					 *  - send(sock, ..., MSG_NOSIGNAL)
+					 *  - setting the signal mask to SIG_IGN during send()
+					 *
+					 * The third method requires three syscalls per send,
+					 * so we prefer either of the first two, but they are
+					 * less portable.  The state is tracked in the following
+					 * members of PGconn:
+					 *
+					 * conn->sigpipe_so		- we have set up SO_NOSIGPIPE
+					 * conn->sigpipe_flag	- we're specifying MSG_NOSIGNAL
+					 *
+					 * If we can use SO_NOSIGPIPE, then set sigpipe_so here
+					 * and we're done.  Otherwise, set sigpipe_flag so that
+					 * we will try MSG_NOSIGNAL on sends.  If we get an error
+					 * with MSG_NOSIGNAL, we'll clear that flag and revert to
+					 * signal masking.
+					 *----------
+					 */
+					conn->sigpipe_so = false;
+#ifdef MSG_NOSIGNAL
+					conn->sigpipe_flag = true;
+#else
+					conn->sigpipe_flag = false;
+#endif /* MSG_NOSIGNAL */
+
+#ifdef SO_NOSIGPIPE
+					optval = 1;
+					if (setsockopt(conn->sock, SOL_SOCKET, SO_NOSIGPIPE,
+								   (char *) &optval, sizeof(optval)) == 0)
+					{
+						conn->sigpipe_so = true;
+						conn->sigpipe_flag = false;
+					}
+#endif /* SO_NOSIGPIPE */
+
 					/*
 					 * Start/make connection.  This should not block, since we
 					 * are in nonblock mode.  If it does, well, too bad.
@@ -1214,7 +1255,6 @@ PQconnectPoll(PGconn *conn)
 
 		case CONNECTION_STARTED:
 			{
-				int			optval;
 				ACCEPT_TYPE_ARG3 optlen = sizeof(optval);
 
 				/*
diff --git a/src/interfaces/libpq/fe-secure.c b/src/interfaces/libpq/fe-secure.c
@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-secure.c,v 1.127 2009/06/23 18:13:23 mha Exp $
+ *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-secure.c,v 1.128 2009/07/24 17:58:31 tgl Exp $
  *
  * NOTES
  *
@@ -118,44 +118,76 @@ static long win32_ssl_create_mutex = 0;
 
 /*
  * Macros to handle disabling and then restoring the state of SIGPIPE handling.
- * Note that DISABLE_SIGPIPE() must appear at the start of a block.
+ * On Windows, these are all no-ops since there's no SIGPIPEs.
  */
 
 #ifndef WIN32
+
+#define SIGPIPE_MASKED(conn)	((conn)->sigpipe_so || (conn)->sigpipe_flag)
+
 #ifdef ENABLE_THREAD_SAFETY
 
-#define DISABLE_SIGPIPE(failaction) \
-	sigset_t	osigmask; \
-	bool		sigpipe_pending; \
-	bool		got_epipe = false; \
-\
-	if (pq_block_sigpipe(&osigmask, &sigpipe_pending) < 0) \
-		failaction
+struct sigpipe_info
+{
+	sigset_t	oldsigmask;
+	bool		sigpipe_pending;
+	bool		got_epipe;
+};
 
-#define REMEMBER_EPIPE(cond) \
+#define DECLARE_SIGPIPE_INFO(spinfo) struct sigpipe_info spinfo
+
+#define DISABLE_SIGPIPE(conn, spinfo, failaction) \
+	do { \
+		(spinfo).got_epipe = false; \
+		if (!SIGPIPE_MASKED(conn)) \
+		{ \
+			if (pq_block_sigpipe(&(spinfo).oldsigmask, \
+								 &(spinfo).sigpipe_pending) < 0) \
+				failaction; \
+		} \
+	} while (0)
+
+#define REMEMBER_EPIPE(spinfo, cond) \
 	do { \
 		if (cond) \
-			got_epipe = true; \
+			(spinfo).got_epipe = true; \
 	} while (0)
 
-#define RESTORE_SIGPIPE() \
-	pq_reset_sigpipe(&osigmask, sigpipe_pending, got_epipe)
-#else							/* !ENABLE_THREAD_SAFETY */
+#define RESTORE_SIGPIPE(conn, spinfo) \
+	do { \
+		if (!SIGPIPE_MASKED(conn)) \
+			pq_reset_sigpipe(&(spinfo).oldsigmask, (spinfo).sigpipe_pending, \
+							 (spinfo).got_epipe); \
+	} while (0)
 
-#define DISABLE_SIGPIPE(failaction) \
-	pqsigfunc	oldsighandler = pqsignal(SIGPIPE, SIG_IGN)
+#else /* !ENABLE_THREAD_SAFETY */
 
-#define REMEMBER_EPIPE(cond)
+#define DECLARE_SIGPIPE_INFO(spinfo) pqsigfunc spinfo = NULL
 
-#define RESTORE_SIGPIPE() \
-	pqsignal(SIGPIPE, oldsighandler)
-#endif   /* ENABLE_THREAD_SAFETY */
-#else							/* WIN32 */
+#define DISABLE_SIGPIPE(conn, spinfo, failaction) \
+	do { \
+		if (!SIGPIPE_MASKED(conn)) \
+			spinfo = pqsignal(SIGPIPE, SIG_IGN); \
+	} while (0)
+
+#define REMEMBER_EPIPE(spinfo, cond)
+
+#define RESTORE_SIGPIPE(conn, spinfo) \
+	do { \
+		if (!SIGPIPE_MASKED(conn)) \
+			pqsignal(SIGPIPE, spinfo); \
+	} while (0)
+
+#endif	/* ENABLE_THREAD_SAFETY */
 
-#define DISABLE_SIGPIPE(failaction)
-#define REMEMBER_EPIPE(cond)
-#define RESTORE_SIGPIPE()
-#endif   /* WIN32 */
+#else	/* WIN32 */
+
+#define DECLARE_SIGPIPE_INFO(spinfo)
+#define DISABLE_SIGPIPE(conn, spinfo, failaction)
+#define REMEMBER_EPIPE(spinfo, cond)
+#define RESTORE_SIGPIPE(conn, spinfo)
+
+#endif	/* WIN32 */
 
 /* ------------------------------------------------------------ */
 /*			 Procedures common to all secure sessions			*/
@@ -231,6 +263,9 @@ pqsecure_open_client(PGconn *conn)
 	/* First time through? */
 	if (conn->ssl == NULL)
 	{
+		/* We cannot use MSG_NOSIGNAL to block SIGPIPE when using SSL */
+		conn->sigpipe_flag = false;
+
 		if (!(conn->ssl = SSL_new(SSL_context)) ||
 			!SSL_set_app_data(conn->ssl, conn) ||
 			!SSL_set_fd(conn->ssl, conn->sock))
@@ -283,9 +318,10 @@ pqsecure_read(PGconn *conn, void *ptr, size_t len)
 	if (conn->ssl)
 	{
 		int			err;
+		DECLARE_SIGPIPE_INFO(spinfo);
 
 		/* SSL_read can write to the socket, so we need to disable SIGPIPE */
-		DISABLE_SIGPIPE(return -1);
+		DISABLE_SIGPIPE(conn, spinfo, return -1);
 
 rloop:
 		n = SSL_read(conn->ssl, ptr, len);
@@ -312,7 +348,7 @@ pqsecure_read(PGconn *conn, void *ptr, size_t len)
 
 					if (n == -1)
 					{
-						REMEMBER_EPIPE(SOCK_ERRNO == EPIPE);
+						REMEMBER_EPIPE(spinfo, SOCK_ERRNO == EPIPE);
 						printfPQExpBuffer(&conn->errorMessage,
 									libpq_gettext("SSL SYSCALL error: %s\n"),
 							SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
@@ -348,7 +384,7 @@ pqsecure_read(PGconn *conn, void *ptr, size_t len)
 				break;
 		}
 
-		RESTORE_SIGPIPE();
+		RESTORE_SIGPIPE(conn, spinfo);
 	}
 	else
 #endif
@@ -364,14 +400,15 @@ ssize_t
 pqsecure_write(PGconn *conn, const void *ptr, size_t len)
 {
 	ssize_t		n;
-
-	DISABLE_SIGPIPE(return -1);
+	DECLARE_SIGPIPE_INFO(spinfo);
 
 #ifdef USE_SSL
 	if (conn->ssl)
 	{
 		int			err;
 
+		DISABLE_SIGPIPE(conn, spinfo, return -1);
+
 		n = SSL_write(conn->ssl, ptr, len);
 		err = SSL_get_error(conn->ssl, n);
 		switch (err)
@@ -396,7 +433,7 @@ pqsecure_write(PGconn *conn, const void *ptr, size_t len)
 
 					if (n == -1)
 					{
-						REMEMBER_EPIPE(SOCK_ERRNO == EPIPE);
+						REMEMBER_EPIPE(spinfo, SOCK_ERRNO == EPIPE);
 						printfPQExpBuffer(&conn->errorMessage,
 									libpq_gettext("SSL SYSCALL error: %s\n"),
 							SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
@@ -434,11 +471,41 @@ pqsecure_write(PGconn *conn, const void *ptr, size_t len)
 	else
 #endif
 	{
-		n = send(conn->sock, ptr, len, 0);
-		REMEMBER_EPIPE(n < 0 && SOCK_ERRNO == EPIPE);
+		int		flags = 0;
+
+#ifdef MSG_NOSIGNAL
+		if (conn->sigpipe_flag)
+			flags |= MSG_NOSIGNAL;
+
+retry_masked:
+
+#endif /* MSG_NOSIGNAL */
+
+		DISABLE_SIGPIPE(conn, spinfo, return -1);
+
+		n = send(conn->sock, ptr, len, flags);
+
+		if (n < 0)
+		{
+			/*
+			 * If we see an EINVAL, it may be because MSG_NOSIGNAL isn't
+			 * available on this machine.  So, clear sigpipe_flag so we don't
+			 * try the flag again, and retry the send().
+			 */
+#ifdef MSG_NOSIGNAL
+			if (flags != 0 && SOCK_ERRNO == EINVAL)
+			{
+				conn->sigpipe_flag = false;
+				flags = 0;
+				goto retry_masked;
+			}
+#endif /* MSG_NOSIGNAL */
+
+			REMEMBER_EPIPE(spinfo, SOCK_ERRNO == EPIPE);
+		}
 	}
 
-	RESTORE_SIGPIPE();
+	RESTORE_SIGPIPE(conn, spinfo);
 
 	return n;
 }
@@ -1220,14 +1287,16 @@ close_SSL(PGconn *conn)
 {
 	if (conn->ssl)
 	{
-		DISABLE_SIGPIPE((void) 0);
+		DECLARE_SIGPIPE_INFO(spinfo);
+
+		DISABLE_SIGPIPE(conn, spinfo, (void) 0);
 		SSL_shutdown(conn->ssl);
 		SSL_free(conn->ssl);
 		conn->ssl = NULL;
 		pqsecure_destroy();
 		/* We have to assume we got EPIPE */
-		REMEMBER_EPIPE(true);
-		RESTORE_SIGPIPE();
+		REMEMBER_EPIPE(spinfo, true);
+		RESTORE_SIGPIPE(conn, spinfo);
 	}
 
 	if (conn->peer)
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.143 2009/06/23 18:13:23 mha Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.144 2009/07/24 17:58:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -341,6 +341,8 @@ struct pg_conn
 	ProtocolVersion pversion;	/* FE/BE protocol version in use */
 	int			sversion;		/* server version, e.g. 70401 for 7.4.1 */
 	bool		password_needed;	/* true if server demanded a password */
+	bool		sigpipe_so;		/* have we masked SIGPIPE via SO_NOSIGPIPE? */
+	bool		sigpipe_flag;	/* can we mask SIGPIPE via MSG_NOSIGNAL? */
 
 	/* Transient state needed while establishing connection */
 	struct addrinfo *addrlist;	/* list of possible backend addresses */
