about summary refs log tree commit diff
path: root/src/time/strftime.c
diff options
context:
space:
mode:
authorRich Felker <dalias@aerifal.cx>2013-08-24 12:59:02 -0400
committerRich Felker <dalias@aerifal.cx>2013-08-24 12:59:02 -0400
commitd78be392e144c338f58ce6a51d82c859126c137d (patch)
tree154cc7c69af95a812cfb2d3dab8622e6f9bd5a77 /src/time/strftime.c
parent0f9b1f672b68b7c3570f07b130cc5c8938b22bad (diff)
downloadmusl-d78be392e144c338f58ce6a51d82c859126c137d.tar.gz
musl-d78be392e144c338f58ce6a51d82c859126c137d.tar.xz
musl-d78be392e144c338f58ce6a51d82c859126c137d.zip
fix strftime handling of time zone data
this may need further revision in the future, since POSIX is rather
unclear on the requirements, and is designed around the assumption of
POSIX TZ specifiers which are not sufficiently powerful to represent
real-world timezones (this is why zoneinfo support was added).

the basic issue is that strftime gets the string and numeric offset
for the timezone from the extra fields in struct tm, which are
initialized when calling localtime/gmtime/etc. however, a conforming
application might have created its own struct tm without initializing
these fields, in which case using __tm_zone (a pointer) could crash.
other zoneinfo-based implementations simply check for a null pointer,
but otherwise can still crash of the field contains junk.

simply ignoring __tm_zone and using tzname[] would "work" but would
give incorrect results in time zones with more complex rules. I feel
like this would lower the quality of implementation.

instead, simply validate __tm_zone: unless it points to one of the
zone name strings managed by the timezone system, assume it's invalid.

this commit also fixes several other minor bugs with formatting:
tm_isdst being negative is required to suppress printing of the zone
formats, and %z was using the wrong format specifiers since the type
of val was changed, resulting in bogus output.
Diffstat (limited to 'src/time/strftime.c')
-rw-r--r--src/time/strftime.c16
1 files changed, 13 insertions, 3 deletions
diff --git a/src/time/strftime.c b/src/time/strftime.c
index 24000f3b..48f65320 100644
--- a/src/time/strftime.c
+++ b/src/time/strftime.c
@@ -43,6 +43,7 @@ static int week_num(const struct tm *tm)
 	return val;
 }
 
+const char *__tm_to_tzname(const struct tm *);
 size_t __strftime_l(char *restrict, size_t, const char *restrict, const struct tm *restrict, locale_t);
 
 const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm *tm, locale_t loc)
@@ -166,11 +167,20 @@ const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm *
 		width = 4;
 		goto number;
 	case 'z':
-		val = -tm->__tm_gmtoff;
-		*l = snprintf(*s, sizeof *s, "%+.2d%.2d", val/3600, abs(val%3600)/60);
+		if (tm->tm_isdst < 0) {
+			*l = 0;
+			return "";
+		}
+		*l = snprintf(*s, sizeof *s, "%+.2d%.2d",
+			(-tm->__tm_gmtoff)/3600,
+			abs(tm->__tm_gmtoff%3600)/60);
 		return *s;
 	case 'Z':
-		fmt = tm->__tm_zone;
+		if (tm->tm_isdst < 0) {
+			*l = 0;
+			return "";
+		}
+		fmt = __tm_to_tzname(tm);
 		goto string;
 	case '%':
 		*l = 1;