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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.
This commit is contained in:
Rich Felker 2015-10-14 18:58:15 -04:00
parent 6fef8cafbd
commit 8d93cb5775
1 changed files with 12 additions and 8 deletions
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20
src/time/strftime.c
View File

@ -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;