In pg_log_generic(), be more paranoid about preserving errno.

tglsfdc · tglsfdc · commit fb30c9c1c5c3 · 2019-07-06T11:25:37.000-04:00
This code failed to account for the possibility that malloc() would change errno, resulting in wrong output for %m, not to mention the possibility of message truncation. Such a change is obviously expected when malloc fails, but there's reason to fear that on some platforms even a successful malloc call can modify errno. Discussion: https://postgr.es/m/2576.1527382833@sss.pgh.pa.us
diff --git a/src/common/logging.c b/src/common/logging.c
@@ -216,6 +216,8 @@ pg_log_generic_v(enum pg_log_level level, const char *pg_restrict fmt, va_list a
 
 	buf = pg_malloc_extended(required_len, MCXT_ALLOC_NO_OOM);
 
+	errno = save_errno;			/* malloc might change errno */
+
 	if (!buf)
 	{
 		/* memory trouble, just print what we can and get out of here */

Original file line number	Diff line number	Diff line change
`@@ -216,6 +216,8 @@ pg_log_generic_v(enum pg_log_level level, const char *pg_restrict fmt, va_list a`
`216`	`216`
`217`	`217`	`buf = pg_malloc_extended(required_len, MCXT_ALLOC_NO_OOM);`
`218`	`218`
	`219`	`+ errno = save_errno; /* malloc might change errno */`
	`220`	`+`
`219`	`221`	`if (!buf)`
`220`	`222`	`{`
`221`	`223`	`/* memory trouble, just print what we can and get out of here */`