!1 CVE-2020-21469 安全更新:In-the-postmaster-rely-on-the-signal-infrastructure

Merge pull request !1 from 吴诚/openkylin/yangtze

src/backend/libpq/pqsignal.c

@@ -95,3 +95,52 @@ pqinitmask(void)
 	sigdelset(&StartupBlockSig, SIGALRM);
 #endif
 }
+
+/*
+ * Set up a postmaster signal handler for signal "signo"
+ *
+ * Returns the previous handler.
+ *
+ * This is used only in the postmaster, which has its own odd approach to
+ * signal handling.  For signals with handlers, we block all signals for the
+ * duration of signal handler execution.  We also do not set the SA_RESTART
+ * flag; this should be safe given the tiny range of code in which the
+ * postmaster ever unblocks signals.
+ *
+ * pqinitmask() must have been invoked previously.
+ *
+ * On Windows, this function is just an alias for pqsignal()
+ * (and note that it's calling the code in src/backend/port/win32/signal.c,
+ * not src/port/pqsignal.c).  On that platform, the postmaster's signal
+ * handlers still have to block signals for themselves.
+ */
+pqsigfunc
+pqsignal_pm(int signo, pqsigfunc func)
+{
+#ifndef WIN32
+	struct sigaction act,
+				oact;
+
+	act.sa_handler = func;
+	if (func == SIG_IGN || func == SIG_DFL)
+	{
+		/* in these cases, act the same as pqsignal() */
+		sigemptyset(&act.sa_mask);
+		act.sa_flags = SA_RESTART;
+	}
+	else
+	{
+		act.sa_mask = BlockSig;
+		act.sa_flags = 0;
+	}
+#ifdef SA_NOCLDSTOP
+	if (signo == SIGCHLD)
+		act.sa_flags |= SA_NOCLDSTOP;
+#endif
+	if (sigaction(signo, &act, &oact) < 0)
+		return SIG_ERR;
+	return oact.sa_handler;
+#else							/* WIN32 */
+	return pqsignal(signo, func);
+#endif
+}

src/backend/postmaster/postmaster.c

@@ -606,14 +606,25 @@ PostmasterMain(int argc, char *argv[])
 	/*
 	 * Set up signal handlers for the postmaster process.
 	 *
-	 * In the postmaster, we want to install non-ignored handlers *without*
-	 * SA_RESTART.  This is because they'll be blocked at all times except
-	 * when ServerLoop is waiting for something to happen, and during that
-	 * window, we want signals to exit the select(2) wait so that ServerLoop
-	 * can respond if anything interesting happened.  On some platforms,
-	 * signals marked SA_RESTART would not cause the select() wait to end.
-	 * Child processes will generally want SA_RESTART, but we expect them to
-	 * set up their own handlers before unblocking signals.
+	 * In the postmaster, we use pqsignal_pm() rather than pqsignal() (which
+	 * is used by all child processes and client processes).  That has a
+	 * couple of special behaviors:
+	 *
+	 * 1. Except on Windows, we tell sigaction() to block all signals for the
+	 * duration of the signal handler.  This is faster than our old approach
+	 * of blocking/unblocking explicitly in the signal handler, and it should
+	 * also prevent excessive stack consumption if signals arrive quickly.
+	 *
+	 * 2. We do not set the SA_RESTART flag.  This is because signals will be
+	 * blocked at all times except when ServerLoop is waiting for something to
+	 * happen, and during that window, we want signals to exit the select(2)
+	 * wait so that ServerLoop can respond if anything interesting happened.
+	 * On some platforms, signals marked SA_RESTART would not cause the
+	 * select() wait to end.
+	 *
+	 * Child processes will generally want SA_RESTART, so pqsignal() sets that
+	 * flag.  We expect children to set up their own handlers before
+	 * unblocking signals.
 	 *
 	 * CAUTION: when changing this list, check for side-effects on the signal
 	 * handling setup of child processes.  See tcop/postgres.c,
@@ -625,18 +636,16 @@ PostmasterMain(int argc, char *argv[])
 	pqinitmask();
 	PG_SETMASK(&BlockSig);
 
-	pqsignal_no_restart(SIGHUP, SIGHUP_handler);	/* reread config file and
-													 * have children do same */
-	pqsignal_no_restart(SIGINT, pmdie); /* send SIGTERM and shut down */
-	pqsignal_no_restart(SIGQUIT, pmdie);	/* send SIGQUIT and die */
-	pqsignal_no_restart(SIGTERM, pmdie);	/* wait for children and shut down */
-	pqsignal(SIGALRM, SIG_IGN); /* ignored */
-	pqsignal(SIGPIPE, SIG_IGN); /* ignored */
-	pqsignal_no_restart(SIGUSR1, sigusr1_handler);	/* message from child
-													 * process */
-	pqsignal_no_restart(SIGUSR2, dummy_handler);	/* unused, reserve for
-													 * children */
-	pqsignal_no_restart(SIGCHLD, reaper);	/* handle child termination */
+	pqsignal_pm(SIGHUP, SIGHUP_handler);	/* reread config file and have
+											 * children do same */
+	pqsignal_pm(SIGINT, pmdie); /* send SIGTERM and shut down */
+	pqsignal_pm(SIGQUIT, pmdie);	/* send SIGQUIT and die */
+	pqsignal_pm(SIGTERM, pmdie);	/* wait for children and shut down */
+	pqsignal_pm(SIGALRM, SIG_IGN);	/* ignored */
+	pqsignal_pm(SIGPIPE, SIG_IGN);	/* ignored */
+	pqsignal_pm(SIGUSR1, sigusr1_handler);	/* message from child process */
+	pqsignal_pm(SIGUSR2, dummy_handler);	/* unused, reserve for children */
+	pqsignal_pm(SIGCHLD, reaper);	/* handle child termination */
 
 	/*
 	 * No other place in Postgres should touch SIGTTIN/SIGTTOU handling.  We
@@ -646,15 +655,15 @@ PostmasterMain(int argc, char *argv[])
 	 * child processes should just allow the inherited settings to stand.
 	 */
 #ifdef SIGTTIN
-	pqsignal(SIGTTIN, SIG_IGN); /* ignored */
+	pqsignal_pm(SIGTTIN, SIG_IGN);	/* ignored */
 #endif
 #ifdef SIGTTOU
-	pqsignal(SIGTTOU, SIG_IGN); /* ignored */
+	pqsignal_pm(SIGTTOU, SIG_IGN);	/* ignored */
 #endif
 
 	/* ignore SIGXFSZ, so that ulimit violations work like disk full */
 #ifdef SIGXFSZ
-	pqsignal(SIGXFSZ, SIG_IGN); /* ignored */
+	pqsignal_pm(SIGXFSZ, SIG_IGN);	/* ignored */
 #endif
 
 	/*
@@ -2627,7 +2636,13 @@ SIGHUP_handler(SIGNAL_ARGS)
 {
 	int			save_errno = errno;
 
+	/*
+	 * We rely on the signal mechanism to have blocked all signals ... except
+	 * on Windows, which lacks sigaction(), so we have to do it manually.
+	 */
+#ifdef WIN32
 	PG_SETMASK(&BlockSig);
+#endif
 
 	if (Shutdown <= SmartShutdown)
 	{
@@ -2687,7 +2702,9 @@ SIGHUP_handler(SIGNAL_ARGS)
 #endif
 	}
 
+#ifdef WIN32
 	PG_SETMASK(&UnBlockSig);
+#endif
 
 	errno = save_errno;
 }
@@ -2701,7 +2718,13 @@ pmdie(SIGNAL_ARGS)
 {
 	int			save_errno = errno;
 
+	/*
+	 * We rely on the signal mechanism to have blocked all signals ... except
+	 * on Windows, which lacks sigaction(), so we have to do it manually.
+	 */
+#ifdef WIN32
 	PG_SETMASK(&BlockSig);
+#endif
 
 	ereport(DEBUG2,
 			(errmsg_internal("postmaster received signal %d",
@@ -2867,7 +2890,9 @@ pmdie(SIGNAL_ARGS)
 			break;
 	}
 
+#ifdef WIN32
 	PG_SETMASK(&UnBlockSig);
+#endif
 
 	errno = save_errno;
 }
@@ -2882,7 +2907,13 @@ reaper(SIGNAL_ARGS)
 	int			pid;			/* process id of dead child process */
 	int			exitstatus;		/* its exit status */
 
+	/*
+	 * We rely on the signal mechanism to have blocked all signals ... except
+	 * on Windows, which lacks sigaction(), so we have to do it manually.
+	 */
+#ifdef WIN32
 	PG_SETMASK(&BlockSig);
+#endif
 
 	ereport(DEBUG4,
 			(errmsg_internal("reaping dead processes")));
@@ -3184,7 +3215,9 @@ reaper(SIGNAL_ARGS)
 	PostmasterStateMachine();
 
 	/* Done with signal handler */
+#ifdef WIN32
 	PG_SETMASK(&UnBlockSig);
+#endif
 
 	errno = save_errno;
 }
@@ -5086,7 +5119,13 @@ sigusr1_handler(SIGNAL_ARGS)
 {
 	int			save_errno = errno;
 
+	/*
+	 * We rely on the signal mechanism to have blocked all signals ... except
+	 * on Windows, which lacks sigaction(), so we have to do it manually.
+	 */
+#ifdef WIN32
 	PG_SETMASK(&BlockSig);
+#endif
 
 	/* Process background worker state change. */
 	if (CheckPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE))
@@ -5244,7 +5283,9 @@ sigusr1_handler(SIGNAL_ARGS)
 		signal_child(StartupPID, SIGUSR2);
 	}
 
+#ifdef WIN32
 	PG_SETMASK(&UnBlockSig);
+#endif
 
 	errno = save_errno;
 }

src/include/libpq/pqsignal.h

@@ -36,4 +36,7 @@ extern sigset_t UnBlockSig,
 
 extern void pqinitmask(void);
 
+/* pqsigfunc is declared in src/include/port.h */
+extern pqsigfunc pqsignal_pm(int signo, pqsigfunc func);
+
 #endif							/* PQSIGNAL_H */

src/include/port.h

@@ -524,11 +524,6 @@ extern int	pg_mkdir_p(char *path, int omode);
 /* port/pqsignal.c */
 typedef void (*pqsigfunc) (int signo);
 extern pqsigfunc pqsignal(int signo, pqsigfunc func);
-#ifndef WIN32
-extern pqsigfunc pqsignal_no_restart(int signo, pqsigfunc func);
-#else
-#define pqsignal_no_restart(signo, func) pqsignal(signo, func)
-#endif
 
 /* port/quotes.c */
 extern char *escape_single_quotes_ascii(const char *src);

src/port/pqsignal.c

@@ -58,33 +58,4 @@ pqsignal(int signo, pqsigfunc func)
 #endif
 }
 
-/*
- * Set up a signal handler, without SA_RESTART, for signal "signo"
- *
- * Returns the previous handler.
- *
- * On Windows, this would be identical to pqsignal(), so don't bother.
- */
-#ifndef WIN32
-
-pqsigfunc
-pqsignal_no_restart(int signo, pqsigfunc func)
-{
-	struct sigaction act,
-				oact;
-
-	act.sa_handler = func;
-	sigemptyset(&act.sa_mask);
-	act.sa_flags = 0;
-#ifdef SA_NOCLDSTOP
-	if (signo == SIGCHLD)
-		act.sa_flags |= SA_NOCLDSTOP;
-#endif
-	if (sigaction(signo, &act, &oact) < 0)
-		return SIG_ERR;
-	return oact.sa_handler;
-}
-
-#endif							/* !WIN32 */
-
 #endif							/* !defined(WIN32) || defined(FRONTEND) */