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.

diff --git a/src/time/strftime.c b/src/time/strftime.c
index e945bb7..f1ccc4d 100644 (file)
--- 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;