Ensure that all temp files made during pg_upgrade are non-world-readable.

pg_upgrade has always attempted to ensure that the transient dump files
it creates are inaccessible except to the owner.  However, refactoring
in commit 76a7650c broke that for the file containing "pg_dumpall -g"
output; since then, that file was protected according to the process's
default umask.  Since that file may contain role passwords (hopefully
encrypted, but passwords nonetheless), this is a particularly unfortunate
oversight.  Prudent users of pg_upgrade on multiuser systems would
probably run it under a umask tight enough that the issue is moot, but
perhaps some users are depending only on pg_upgrade's umask changes to
protect their data.

To fix this in a future-proof way, let's just tighten the umask at
process start.  There are no files pg_upgrade needs to write at a
weaker security level; and if there were, transiently relaxing the
umask around where they're created would be a safer approach.

Report and patch by Tom Lane; the idea for the fix is due to Noah Misch.
Back-patch to all supported branches.

Security: CVE-2018-1053

src/bin/pg_upgrade/dump.c

@@ -18,7 +18,6 @@ void
 generate_old_dump(void)
 {
 	int			dbnum;
-	mode_t		old_umask;
 
 	prep_status("Creating dump of global objects");
 
@@ -33,13 +32,6 @@ generate_old_dump(void)
 
 	prep_status("Creating dump of database schemas\n");
 
-	/*
-	 * Set umask for this function, all functions it calls, and all
-	 * subprocesses/threads it creates.  We can't use fopen_priv() as Windows
-	 * uses threads and umask is process-global.
-	 */
-	old_umask = umask(S_IRWXG | S_IRWXO);
-
 	/* create per-db dump files */
 	for (dbnum = 0; dbnum < old_cluster.dbarr.ndbs; dbnum++)
 	{
@@ -74,8 +66,6 @@ generate_old_dump(void)
 	while (reap_child(true) == true)
 		;
 
-	umask(old_umask);
-
 	end_progress_output();
 	check_ok();
 }

src/bin/pg_upgrade/file.c

@@ -314,18 +314,3 @@ win32_pghardlink(const char *src, const char *dst)
 		return 0;
 }
 #endif
-
-
-/* fopen() file with no group/other permissions */
-FILE *
-fopen_priv(const char *path, const char *mode)
-{
-	mode_t		old_umask = umask(S_IRWXG | S_IRWXO);
-	FILE	   *fp;
-
-	fp = fopen(path, mode);
-
-	umask(old_umask);			/* we assume this can't change errno */
-
-	return fp;
-}

src/bin/pg_upgrade/pg_upgrade.c

@@ -77,6 +77,10 @@ main(int argc, char **argv)
 	bool		live_check = false;
 
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_upgrade"));
+
+	/* Ensure that all files created by pg_upgrade are non-world-readable */
+	umask(S_IRWXG | S_IRWXO);
+
 	parseCommandLine(argc, argv);
 
 	get_restricted_token(os_info.progname);

src/bin/pg_upgrade/pg_upgrade.h

@@ -374,7 +374,9 @@ void linkFile(const char *src, const char *dst,
 void rewriteVisibilityMap(const char *fromfile, const char *tofile,
 					 const char *schemaName, const char *relName);
 void		check_hard_link(void);
-FILE	   *fopen_priv(const char *path, const char *mode);
+
+/* fopen_priv() is no longer different from fopen() */
+#define fopen_priv(path, mode)	fopen(path, mode)
 
 /* function.c */