From 8d93cb57754f1f81f8e15bb74afd1725cead45c2 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Wed, 14 Oct 2015 18:58:15 -0400 Subject: [PATCH] fix strftime handling of out-of-range struct tm fields strftime results are unspecified in this case, but should not invoke undefined behaviour. tm_wday, tm_yday, tm_mon and tm_year fields were used in signed int arithmetic that could overflow. based on patch by Szabolcs Nagy. --- src/time/strftime.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/src/time/strftime.c b/src/time/strftime.c index e945bb7d..f1ccc4dd 100644 --- a/src/time/strftime.c +++ b/src/time/strftime.c @@ -21,24 +21,24 @@ static int is_leap(int y) static int week_num(const struct tm *tm) { - int val = (tm->tm_yday + 7 - (tm->tm_wday+6)%7) / 7; + int val = (tm->tm_yday + 7U - (tm->tm_wday+6U)%7) / 7; /* If 1 Jan is just 1-3 days past Monday, * the previous week is also in this year. */ - if ((tm->tm_wday - tm->tm_yday - 2 + 371) % 7 <= 2) + if ((tm->tm_wday + 371U - tm->tm_yday - 2) % 7 <= 2) val++; if (!val) { val = 52; /* If 31 December of prev year a Thursday, * or Friday of a leap year, then the * prev year has 53 weeks. */ - int dec31 = (tm->tm_wday - tm->tm_yday - 1 + 7) % 7; + int dec31 = (tm->tm_wday + 7U - tm->tm_yday - 1) % 7; if (dec31 == 4 || (dec31 == 5 && is_leap(tm->tm_year%400-1))) val++; } else if (val == 53) { /* If 1 January is not a Thursday, and not * a Wednesday of a leap year, then this * year has only 52 weeks. */ - int jan1 = (tm->tm_wday - tm->tm_yday + 371) % 7; + int jan1 = (tm->tm_wday + 371U - tm->tm_yday) % 7; if (jan1 != 4 && (jan1 != 3 || !is_leap(tm->tm_year))) val = 1; } @@ -52,21 +52,25 @@ const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm * { nl_item item; long long val; - const char *fmt; + const char *fmt = "-"; int width = 2; switch (f) { case 'a': + if (tm->tm_wday > 6U) goto string; item = ABDAY_1 + tm->tm_wday; goto nl_strcat; case 'A': + if (tm->tm_wday > 6U) goto string; item = DAY_1 + tm->tm_wday; goto nl_strcat; case 'h': case 'b': + if (tm->tm_mon > 11U) goto string; item = ABMON_1 + tm->tm_mon; goto nl_strcat; case 'B': + if (tm->tm_mon > 11U) goto string; item = MON_1 + tm->tm_mon; goto nl_strcat; case 'c': @@ -143,10 +147,10 @@ const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm * width = 1; goto number; case 'U': - val = (tm->tm_yday + 7 - tm->tm_wday) / 7; + val = (tm->tm_yday + 7U - tm->tm_wday) / 7; goto number; case 'W': - val = (tm->tm_yday + 7 - (tm->tm_wday+6)%7) / 7; + val = (tm->tm_yday + 7U - (tm->tm_wday+6U)%7) / 7; goto number; case 'V': val = week_num(tm); @@ -165,7 +169,7 @@ const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm * val = tm->tm_year % 100; goto number; case 'Y': - val = tm->tm_year + 1900; + val = tm->tm_year + 1900LL; if (val >= 10000) { *l = snprintf(*s, sizeof *s, "+%lld", val); return *s; -- 2.25.1