Avoid possibly-unsafe use of Windows' FormatMessage() function.

Whenever this function is used with the FORMAT_MESSAGE_FROM_SYSTEM flag,
it's good practice to include FORMAT_MESSAGE_IGNORE_INSERTS as well.
Otherwise, if the message contains any %n insertion markers, the function
will try to fetch argument strings to substitute --- which we are not
passing, possibly leading to a crash.  This is exactly analogous to the
rule about not giving printf() a format string you're not in control of.

Noted and patched by Christian Ullrich.
Back-patch to all supported branches.

src/backend/libpq/auth.c

@@ -1011,7 +1011,9 @@ pg_SSPI_error(int severity, const char *errmsg, SECURITY_STATUS r)
 {
 	char		sysmsg[256];
 
-	if (FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, NULL, r, 0,
+	if (FormatMessage(FORMAT_MESSAGE_IGNORE_INSERTS |
+					  FORMAT_MESSAGE_FROM_SYSTEM,
+					  NULL, r, 0,
 					  sysmsg, sizeof(sysmsg), NULL) == 0)
 		ereport(severity,
 				(errmsg_internal("%s", errmsg),

src/backend/port/win32/socket.c

@@ -658,7 +658,9 @@ pgwin32_socket_strerror(int err)
 	}
 
 	ZeroMemory(&wserrbuf, sizeof(wserrbuf));
-	if (FormatMessage(FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_FROM_HMODULE,
+	if (FormatMessage(FORMAT_MESSAGE_IGNORE_INSERTS |
+					  FORMAT_MESSAGE_FROM_SYSTEM |
+					  FORMAT_MESSAGE_FROM_HMODULE,
 					  handleDLL,
 					  err,
 					  MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),

src/interfaces/libpq/fe-auth.c

@@ -234,7 +234,9 @@ pg_SSPI_error(PGconn *conn, const char *mprefix, SECURITY_STATUS r)
 {
 	char		sysmsg[256];
 
-	if (FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, NULL, r, 0,
+	if (FormatMessage(FORMAT_MESSAGE_IGNORE_INSERTS |
+					  FORMAT_MESSAGE_FROM_SYSTEM,
+					  NULL, r, 0,
 					  sysmsg, sizeof(sysmsg), NULL) == 0)
 		printfPQExpBuffer(&conn->errorMessage, "%s: SSPI error %x\n",
 						  mprefix, (unsigned int) r);

src/port/dirmod.c

@@ -206,7 +206,9 @@ pgsymlink(const char *oldpath, const char *newpath)
 		LPSTR		msg;
 
 		errno = 0;
-		FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
+		FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
+					  FORMAT_MESSAGE_IGNORE_INSERTS |
+					  FORMAT_MESSAGE_FROM_SYSTEM,
 					  NULL, GetLastError(),
 					  MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
 					  (LPSTR) &msg, 0, NULL);
@@ -281,7 +283,9 @@ pgreadlink(const char *path, char *buf, size_t size)
 		LPSTR		msg;
 
 		errno = 0;
-		FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
+		FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
+					  FORMAT_MESSAGE_IGNORE_INSERTS |
+					  FORMAT_MESSAGE_FROM_SYSTEM,
 					  NULL, GetLastError(),
 					  MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
 					  (LPSTR) &msg, 0, NULL);