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string.c: check the append size before mrb_str_cat() modifies #7038

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Merged
matz merged 1 commit into from
Aug 9, 2026
Merged

string.c: check the append size before mrb_str_cat() modifies #7038

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15 changes: 10 additions & 5 deletions src/string.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3136,17 +3136,22 @@ mrb_str_cat(mrb_state *mrb, mrb_value str, const char *ptr, size_t len)
ptrdiff_t off = -1;

if (len == 0) return str;
/* `len` has to be known to fit in an `mrb_int` before it is used as one:
the conversion is otherwise free to make it negative, and the overflow
check takes `mrb_int` parameters, so it would not see it. Checking ahead
of the modification also leaves the string untouched when it raises. */
mrb_int total;
if (len > (size_t)MRB_INT_MAX ||
mrb_int_add_overflow(RSTR_LEN(s), (mrb_int)len, &total)) {
size_error:
mrb_raise(mrb, E_ARGUMENT_ERROR, "string size too big");
}
mrb_str_modify(mrb, s);
if (ptr >= RSTR_PTR(s) && ptr <= RSTR_PTR(s) + (size_t)RSTR_LEN(s)) {
off = ptr - RSTR_PTR(s);
}

mrb_int capa = RSTR_CAPA(s);
mrb_int total;
if (mrb_int_add_overflow(RSTR_LEN(s), len, &total)) {
size_error:
mrb_raise(mrb, E_ARGUMENT_ERROR, "string size too big");
}
if (capa <= total) {
if (capa == 0) capa = 1;
while (capa <= total) {
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