Fix unsafe usage of strerror(errno) within ereport().

tglsfdc · tglsfdc · commit 5517367e978b · 2018-05-21T00:32:52.000-04:00
This is the converse of the unsafe-usage-of-%m problem: the reason
ereport/elog provide that format code is mainly to dodge the hazard
of errno getting changed before control reaches functions within the
arguments of the macro.  I only found one instance of this hazard,
but it's been there since 9.4 :-(.
diff --git a/src/backend/libpq/auth.c b/src/backend/libpq/auth.c
@@ -1615,10 +1615,12 @@ auth_peer(hbaPort *port)
 	pw = getpwuid(uid);
 	if (!pw)
 	{
+		int			save_errno = errno;
+
 		ereport(LOG,
 				(errmsg("could not look up local user ID %ld: %s",
 						(long) uid,
-						errno ? strerror(errno) : _("user does not exist"))));
+						save_errno ? strerror(save_errno) : _("user does not exist"))));
 		return STATUS_ERROR;
 	}
 

Original file line number	Diff line number	Diff line change
`@@ -1615,10 +1615,12 @@ auth_peer(hbaPort *port)`
`1615`	`1615`	`pw = getpwuid(uid);`
`1616`	`1616`	`if (!pw)`
`1617`	`1617`	`{`
	`1618`	`+ int save_errno = errno;`
	`1619`	`+`
`1618`	`1620`	`ereport(LOG,`
`1619`	`1621`	`(errmsg("could not look up local user ID %ld: %s",`
`1620`	`1622`	`(long) uid,`
`1621`		`- errno ? strerror(errno) : _("user does not exist"))));`
	`1623`	`+ save_errno ? strerror(save_errno) : _("user does not exist"))));`
`1622`	`1624`	`return STATUS_ERROR;`
`1623`	`1625`	`}`
`1624`	`1626`