On Wed, Feb 03, 2021 at 04:50:07PM +0000, Richard Fitzgerald wrote:
> The existing code attempted to handle numbers by doing a strto[u]l(),
> ignoring the field width, and then repeatedly dividing to extract the
> field out of the full converted value. If the string contains a run of
> valid digits longer than will fit in a long or long long, this would
> overflow and no amount of dividing can recover the correct value.
>
> This patch fixes vsscanf to obey number field widths when parsing
vsscanf()
> the number.
>
> A new _parse_integer_limit() is added that takes a limit for the number
> of characters to parse. The number field conversion in vsscanf is changed
> to use this new function.
>
> If a number starts with a radix prefix, the field width must be long
> enough for at last one digit after the prefix. If not, it will be handled
> like this:
>
> sscanf("0x4", "%1i", &i): i=0, scanning continues with the 'x'
> sscanf("0x4", "%2i", &i): i=0, scanning continues with the '4'
>
> This is consistent with the observed behaviour of userland sscanf.
>
> Note that this patch does NOT fix the problem of a single field value
> overflowing the target type. So for example:
>
> sscanf("123456789abcdef", "%x", &i);
>
> Will not produce the correct result because the value obviously overflows
> INT_MAX. But sscanf will report a successful conversion.
...
> + for (; max_chars > 0; max_chars--) {
Less fragile is to write
while (max_chars--)
This allows max_char to be an unsigned type.
Moreover...
> + return _parse_integer_limit(s, base, p, INT_MAX);
You have inconsistency with INT_MAX vs, size_t above.
...
> +unsigned int _parse_integer_limit(const char *s, unsigned int base,
> + unsigned long long *res, size_t max_chars);
Also, can you leave res on previous line, so it will be easier to see what's
the difference with the original one?
> unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long *res);
...
> - unsigned long long result;
> + const char *cp;
> + unsigned long long result = 0ULL;
> unsigned int rv;
>
> - cp = _parse_integer_fixup_radix(cp, &base);
> - rv = _parse_integer(cp, base, &result);
> + if (max_chars == 0) {
> + cp = startp;
> + goto out;
> + }
It's redundant if I'm not mistaken.
> + cp = _parse_integer_fixup_radix(startp, &base);
> + if ((cp - startp) >= max_chars) {
> + cp = startp + max_chars;
> + goto out;
> + }
This will be exactly the same, no?
Moreover you will have while (max_chars--) in the _limit() variant which is
also a no-op.
...
> -
Unrelated change.
> +out:
> if (endp)
> *endp = (char *)cp;
--
With Best Regards,
Andy Shevchenko
