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[Repo Assist] fix: clamp INT_MIN dynamic width in l_vsnprintf to avoid UB #151

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[Repo Assist] fix: clamp INT_MIN dynamic width in l_vsnprintf to avoid UB #151

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2 changes: 1 addition & 1 deletion l_os.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3338,7 +3338,7 @@ static inline int l_vsnprintf(char *buf, size_t n, const char *fmt, va_list ap)
}

int width = 0;
if (*fmt == '*') { fmt++; width = va_arg(ap, int); if (width < 0) { flag_minus = 1; width = -width; } }
if (*fmt == '*') { fmt++; width = va_arg(ap, int); if (width < 0) { flag_minus = 1; width = (width == INT_MIN) ? INT_MAX : -width; } }
else while (*fmt >= '0' && *fmt <= '9') width = width * 10 + (*fmt++ - '0');

int prec = -1;
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8 changes: 8 additions & 0 deletions tests/test_strings.c
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Expand Up @@ -1352,6 +1352,14 @@ void test_snprintf(void) {
l_snprintf(buf, sizeof(buf), "%*d", -6, 42);
TEST_ASSERT(l_strcmp(buf, "42 ") == 0, "%*d negative width = left-align");

/* INT_MIN as dynamic width must not overflow — treated as left-align with large pad */
{
int r = l_snprintf(buf, sizeof(buf), "%*d", INT_MIN, 42);
/* content "42" comes first (left-aligned), followed by padding spaces */
TEST_ASSERT(buf[0] == '4' && buf[1] == '2', "%*d INT_MIN width: digits correct");
TEST_ASSERT(r > 0, "%*d INT_MIN width: return value positive (no overflow)");
}

/* dynamic precision: %.*s */
l_snprintf(buf, sizeof(buf), "%.*s", 3, "hello");
TEST_ASSERT(l_strcmp(buf, "hel") == 0, "%.*s precision from va_arg");
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