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libc: actual overrun checks in strftime; fix %z to use proper format
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@klange
klange committed Dec 23, 2023
1 parent 7aaeec1 commit a535a2c
Showing 1 changed file with 50 additions and 44 deletions.
94 changes: 50 additions & 44 deletions libc/time/strftime.c
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Original file line number Diff line number Diff line change
Expand Up @@ -38,15 +38,15 @@ static char * months_short[] = {

size_t strftime(char *s, size_t max, const char *fmt, const struct tm *tm) {
if (!tm) {
if (max < sizeof("[tm is null]")) return 0;
return sprintf(s, "[tm is null]");
}
char * b = s;
size_t count = 0;
for (const char *f = fmt; *f; f++) {
if (*f != '%') {
count++;
if (max == 0) return 0;
max--;
*b++ = *f;
if (count == max) return b - s;
continue;
}
++f;
Expand All @@ -61,22 +61,23 @@ size_t strftime(char *s, size_t max, const char *fmt, const struct tm *tm) {
}
(void)_alte; /* TODO: Implement these */
(void)_alto;
int w = 0;
switch (*f) {
case 'a':
b += sprintf(b, "%s", weekdays_short[tm->tm_wday]);
w = snprintf(b, max, "%s", weekdays_short[tm->tm_wday]);
break;
case 'A':
b += sprintf(b, "%s", weekdays[tm->tm_wday]);
w = snprintf(b, max, "%s", weekdays[tm->tm_wday]);
break;
case 'h':
case 'b':
b += sprintf(b, "%s", months_short[tm->tm_mon]);
w = snprintf(b, max, "%s", months_short[tm->tm_mon]);
break;
case 'B':
b += sprintf(b, "%s", months[tm->tm_mon]);
w = snprintf(b, max, "%s", months[tm->tm_mon]);
break;
case 'c':
b += sprintf(b, "%s %s %02d %02d:%02d:%02d %04d",
w = snprintf(b, max, "%s %s %02d %02d:%02d:%02d %04d",
weekdays_short[tm->tm_wday],
months_short[tm->tm_mon],
tm->tm_mday,
Expand All @@ -86,119 +87,124 @@ size_t strftime(char *s, size_t max, const char *fmt, const struct tm *tm) {
tm->tm_year + 1900);
break;
case 'C':
b += sprintf(b, "%02d", (tm->tm_year + 1900) / 100);
w = snprintf(b, max, "%02d", (tm->tm_year + 1900) / 100);
break;
case 'd':
b += sprintf(b, "%02d", tm->tm_mday);
w = snprintf(b, max, "%02d", tm->tm_mday);
break;
case 'D':
b += sprintf(b, "%02d/%02d/%02d", tm->tm_mon+1, tm->tm_mday, tm->tm_year % 100);
w = snprintf(b, max, "%02d/%02d/%02d", tm->tm_mon+1, tm->tm_mday, tm->tm_year % 100);
break;
case 'e':
b += sprintf(b, "%2d", tm->tm_mday);
w = snprintf(b, max, "%2d", tm->tm_mday);
break;
case 'F':
b += sprintf(b, "%04d-%02d-%02d", tm->tm_year + 1900, tm->tm_mon+1, tm->tm_mday);
w = snprintf(b, max, "%04d-%02d-%02d", tm->tm_year + 1900, tm->tm_mon+1, tm->tm_mday);
break;
case 'H':
b += sprintf(b, "%02d", tm->tm_hour);
w = snprintf(b, max, "%02d", tm->tm_hour);
break;
case 'I':
b += sprintf(b, "%02d", tm->tm_hour == 0 ? 12 : (tm->tm_hour == 12 ? 12 : (tm->tm_hour % 12)));
w = snprintf(b, max, "%02d", tm->tm_hour == 0 ? 12 : (tm->tm_hour == 12 ? 12 : (tm->tm_hour % 12)));
break;
case 'j':
b += sprintf(b, "%03d", tm->tm_yday);
w = snprintf(b, max, "%03d", tm->tm_yday);
break;
case 'k':
b += sprintf(b, "%2d", tm->tm_hour);
w = snprintf(b, max, "%2d", tm->tm_hour);
break;
case 'l':
b += sprintf(b, "%2d", tm->tm_hour == 0 ? 12 : (tm->tm_hour == 12 ? 12 : (tm->tm_hour % 12)));
w = snprintf(b, max, "%2d", tm->tm_hour == 0 ? 12 : (tm->tm_hour == 12 ? 12 : (tm->tm_hour % 12)));
break;
case 'm':
b += sprintf(b, "%02d", tm->tm_mon+1);
w = snprintf(b, max, "%02d", tm->tm_mon+1);
break;
case 'M':
b += sprintf(b, "%02d", tm->tm_min);
w = snprintf(b, max, "%02d", tm->tm_min);
break;
case 'n':
b += sprintf(b, "\n");
w = snprintf(b, max, "\n");
break;
case 'p':
b += sprintf(b, "%s", tm->tm_hour < 12 ? "AM" : "PM");
w = snprintf(b, max, "%s", tm->tm_hour < 12 ? "AM" : "PM");
break;
case 'P':
b += sprintf(b, "%s", tm->tm_hour < 12 ? "am" : "pm");
w = snprintf(b, max, "%s", tm->tm_hour < 12 ? "am" : "pm");
break;
case 'r':
b += sprintf(b, "%02d:%02d:%02d %s",
w = snprintf(b, max, "%02d:%02d:%02d %s",
tm->tm_hour == 0 ? 12 : (tm->tm_hour == 12 ? 12 : (tm->tm_hour % 12)),
tm->tm_min,
tm->tm_sec,
tm->tm_hour < 12 ? "AM" : "PM");
break;
case 'R':
b += sprintf(b, "%02d:%02d",
w = snprintf(b, max, "%02d:%02d",
tm->tm_hour,
tm->tm_min);
break;
case 's':
b += sprintf(b, "%ld", mktime((struct tm*)tm));
w = snprintf(b, max, "%ld", mktime((struct tm*)tm));
break;
case 'S':
b += sprintf(b, "%02d", tm->tm_sec);
w = snprintf(b, max, "%02d", tm->tm_sec);
break;
case 't':
b += sprintf(b, "\t");
w = snprintf(b, max, "\t");
break;
case 'T':
b += sprintf(b, "%02d:%02d:%02d",
w = snprintf(b, max, "%02d:%02d:%02d",
tm->tm_hour,
tm->tm_min,
tm->tm_sec);
break;
case 'u':
b += sprintf(b, "%d", tm->tm_wday == 0 ? 7 : tm->tm_wday);
w = snprintf(b, max, "%d", tm->tm_wday == 0 ? 7 : tm->tm_wday);
break;
case 'w':
b += sprintf(b, "%d", tm->tm_wday);
w = snprintf(b, max, "%d", tm->tm_wday);
break;
case 'x':
b += sprintf(b, "%02d/%02d/%02d", tm->tm_mon+1, tm->tm_mday, tm->tm_year % 100);
w = snprintf(b, max, "%02d/%02d/%02d", tm->tm_mon+1, tm->tm_mday, tm->tm_year % 100);
break;
case 'X':
b += sprintf(b, "%02d:%02d:%02d",
w = snprintf(b, max, "%02d:%02d:%02d",
tm->tm_hour,
tm->tm_min,
tm->tm_sec);
break;
case 'y':
b += sprintf(b, "%02d", tm->tm_year % 100);
w = snprintf(b, max, "%02d", tm->tm_year % 100);
break;
case 'Y':
b += sprintf(b, "%04d", tm->tm_year + 1900);
w = snprintf(b, max, "%04d", tm->tm_year + 1900);
break;
case 'z':
if (tm->_tm_zone_offset >= 0) {
b += sprintf(b, "+%04d", tm->_tm_zone_offset);
} else {
b += sprintf(b, "-%04d", -tm->_tm_zone_offset);
}
case 'z': {
int zone_offset = tm->_tm_zone_offset >= 0 ? tm->_tm_zone_offset : -tm->_tm_zone_offset;
char sign = tm->_tm_zone_offset >= 0 ? '+' : '-';
int hour = zone_offset / 3600;
int mins = (zone_offset / 60) % 60;
w = snprintf(b, max, "%c%02d%02d", sign, hour, mins);
break;
}
case 'Z':
b += sprintf(b, tm->_tm_zone_name);
w = snprintf(b, max, tm->_tm_zone_name);
break;
case '%':
b += sprintf(b, "%c", '%');
w = snprintf(b, max, "%c", '%');
break;
case 'V':
case 'W':
case 'U':
case 'G':
case 'g':
b += sprintf(b, "<%c unsupported>", *f);
w = snprintf(b, max, "<%c unsupported>", *f);
break;
}
if (w < 0) return 0; /* error while formatting */
if ((size_t)w >= max) return 0; /* output was truncated */
max -= w;
b += w;
}
/* Ensure the buffer ends in a null */
*b = '\0';
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