Use explicit_bzero

Use the explicit_bzero() function in places where it is important that
security information such as passwords is cleared from memory.  There
might be other places where it could be useful; this is just an
initial collection.

For platforms that don't have explicit_bzero(), provide various
fallback implementations.  (explicit_bzero() itself isn't standard,
but as Linux/glibc, FreeBSD, and OpenBSD have it, it's the most common
spelling, so it makes sense to make that the invocation point.)

Discussion: https://www.postgresql.org/message-id/flat/42d26bde-5d5b-c90d-87ae-6cab875f73be%402ndquadrant.com

configure

@@ -15087,7 +15087,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in cbrt clock_gettime copyfile fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open strchrnul strsignal symlink sync_file_range uselocale utime utimes wcstombs_l
+for ac_func in cbrt clock_gettime copyfile fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memset_s memmove poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink setproctitle setproctitle_fast setsid shm_open strchrnul strsignal symlink sync_file_range uselocale utime utimes wcstombs_l
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
@@ -15739,6 +15739,19 @@ esac
 
 fi
 
+ac_fn_c_check_func "$LINENO" "explicit_bzero" "ac_cv_func_explicit_bzero"
+if test "x$ac_cv_func_explicit_bzero" = xyes; then :
+  $as_echo "#define HAVE_EXPLICIT_BZERO 1" >>confdefs.h
+
+else
+  case " $LIBOBJS " in
+  *" explicit_bzero.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS explicit_bzero.$ac_objext"
+ ;;
+esac
+
+fi
+
 ac_fn_c_check_func "$LINENO" "fls" "ac_cv_func_fls"
 if test "x$ac_cv_func_fls" = xyes; then :
   $as_echo "#define HAVE_FLS 1" >>confdefs.h

configure.in

@@ -1594,6 +1594,7 @@ AC_CHECK_FUNCS(m4_normalize([
 	getpeerucred
 	getrlimit
 	mbstowcs_l
+	memset_s
 	memmove
 	poll
 	posix_fallocate
@@ -1691,6 +1692,7 @@ fi
 
 AC_REPLACE_FUNCS(m4_normalize([
 	dlopen
+	explicit_bzero
 	fls
 	getopt
 	getrusage

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

@@ -87,6 +87,7 @@ run_ssl_passphrase_command(const char *prompt, bool is_server_start, char *buf,
 	{
 		if (ferror(fh))
 		{
+			explicit_bzero(buf, size);
 			ereport(loglevel,
 					(errcode_for_file_access(),
 					 errmsg("could not read from command \"%s\": %m",
@@ -98,6 +99,7 @@ run_ssl_passphrase_command(const char *prompt, bool is_server_start, char *buf,
 	pclose_rc = ClosePipeStream(fh);
 	if (pclose_rc == -1)
 	{
+		explicit_bzero(buf, size);
 		ereport(loglevel,
 				(errcode_for_file_access(),
 				 errmsg("could not close pipe to external command: %m")));
@@ -105,6 +107,7 @@ run_ssl_passphrase_command(const char *prompt, bool is_server_start, char *buf,
 	}
 	else if (pclose_rc != 0)
 	{
+		explicit_bzero(buf, size);
 		ereport(loglevel,
 				(errcode_for_file_access(),
 				 errmsg("command \"%s\" failed",

src/include/pg_config.h.in

@@ -195,6 +195,9 @@
 /* Define to 1 if you have the <editline/readline.h> header file. */
 #undef HAVE_EDITLINE_READLINE_H
 
+/* Define to 1 if you have the `explicit_bzero' function. */
+#undef HAVE_EXPLICIT_BZERO
+
 /* Define to 1 if you have the `fdatasync' function. */
 #undef HAVE_FDATASYNC
 
@@ -395,6 +398,9 @@
 /* Define to 1 if you have the <memory.h> header file. */
 #undef HAVE_MEMORY_H
 
+/* Define to 1 if you have the `memset_s' function. */
+#undef HAVE_MEMSET_S
+
 /* Define to 1 if the system has the type `MINIDUMP_TYPE'. */
 #undef HAVE_MINIDUMP_TYPE
 

src/include/pg_config.h.win32

@@ -153,6 +153,9 @@
 /* Define to 1 if you have the <editline/readline.h> header file. */
 /* #undef HAVE_EDITLINE_READLINE_H */
 
+/* Define to 1 if you have the `explicit_bzero' function. */
+/* #undef HAVE_EXPLICIT_BZERO */
+
 /* Define to 1 if you have the `fdatasync' function. */
 /* #undef HAVE_FDATASYNC */
 
@@ -283,6 +286,9 @@
 /* Define to 1 if you have the <memory.h> header file. */
 #define HAVE_MEMORY_H 1
 
+/* Define to 1 if you have the `memset_s' function. */
+/* #undef HAVE_MEMSET_S */
+
 /* Define to 1 if the system has the type `MINIDUMP_TYPE'. */
 #define HAVE_MINIDUMP_TYPE 1
 

src/include/port.h

@@ -378,6 +378,10 @@ extern int	isinf(double x);
 #endif							/* __clang__ && !__cplusplus */
 #endif							/* !HAVE_ISINF */
 
+#ifndef HAVE_EXPLICIT_BZERO
+extern void explicit_bzero(void *buf, size_t len);
+#endif
+
 #ifndef HAVE_STRTOF
 extern float strtof(const char *nptr, char **endptr);
 #endif

src/interfaces/libpq/fe-connect.c

@@ -3885,7 +3885,10 @@ freePGconn(PGconn *conn)
 			if (conn->connhost[i].port != NULL)
 				free(conn->connhost[i].port);
 			if (conn->connhost[i].password != NULL)
+			{
+				explicit_bzero(conn->connhost[i].password, strlen(conn->connhost[i].password));
 				free(conn->connhost[i].password);
+			}
 		}
 		free(conn->connhost);
 	}
@@ -3919,7 +3922,10 @@ freePGconn(PGconn *conn)
 	if (conn->pguser)
 		free(conn->pguser);
 	if (conn->pgpass)
+	{
+		explicit_bzero(conn->pgpass, strlen(conn->pgpass));
 		free(conn->pgpass);
+	}
 	if (conn->pgpassfile)
 		free(conn->pgpassfile);
 	if (conn->keepalives)
@@ -6931,6 +6937,7 @@ passwordFromFile(const char *hostname, const char *port, const char *dbname,
 		if (!ret)
 		{
 			/* Out of memory. XXX: an error message would be nice. */
+			explicit_bzero(buf, sizeof(buf));
 			return NULL;
 		}
 
@@ -6947,6 +6954,7 @@ passwordFromFile(const char *hostname, const char *port, const char *dbname,
 	}
 
 	fclose(fp);
+	explicit_bzero(buf, sizeof(buf));
 	return NULL;
 
 #undef LINELEN

src/port/explicit_bzero.c

@@ -0,0 +1,55 @@
+/*-------------------------------------------------------------------------
+ *
+ * explicit_bzero.c
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/port/explicit_bzero.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "c.h"
+
+#if defined(HAVE_MEMSET_S)
+
+void
+explicit_bzero(void *buf, size_t len)
+{
+	(void) memset_s(buf, len, 0, len);
+}
+
+#elif defined(WIN32)
+
+void
+explicit_bzero(void *buf, size_t len)
+{
+	(void) SecureZeroMemory(buf, len);
+}
+
+#else
+
+/*
+ * Indirect call through a volatile pointer to hopefully avoid dead-store
+ * optimisation eliminating the call.  (Idea taken from OpenSSH.)  We can't
+ * assume bzero() is present either, so for simplicity we define our own.
+ */
+
+static void
+bzero2(void *buf, size_t len)
+{
+	memset(buf, 0, len);
+}
+
+static void (* volatile bzero_p)(void *, size_t) = bzero2;
+
+void
+explicit_bzero(void *buf, size_t len)
+{
+	bzero_p(buf, len);
+}
+
+#endif

src/tools/msvc/Mkvcbuild.pm

@@ -93,7 +93,7 @@ sub mkvcbuild
 	$solution = CreateSolution($vsVersion, $config);
 
 	our @pgportfiles = qw(
-	  chklocale.c fls.c fseeko.c getrusage.c inet_aton.c random.c
+	  chklocale.c explicit_bzero.c fls.c fseeko.c getrusage.c inet_aton.c random.c
 	  srandom.c getaddrinfo.c gettimeofday.c inet_net_ntop.c kill.c open.c
 	  erand48.c snprintf.c strlcat.c strlcpy.c dirmod.c noblock.c path.c
 	  dirent.c dlopen.c getopt.c getopt_long.c