On Mon, Feb 08, 2021 at 02:01:52PM +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 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.
I have a few nit-picks, but it's up to you and maintainers how to proceed.
...
-unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base) +static unsigned long long simple_strntoull(const char *startp, size_t max_chars,
char **endp, unsigned int base){
- 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);
- cp = _parse_integer_fixup_radix(startp, &base);
- if ((cp - startp) >= max_chars) {
cp = startp + max_chars;goto out;- }
- max_chars -= (cp - startp);
- rv = _parse_integer_limit(cp, base, &result, max_chars); /* FIXME */ cp += (rv & ~KSTRTOX_OVERFLOW);
+out: if (endp) *endp = (char *)cp; return result; }
A nit-pick: What if we rewrite above as
static unsigned long long simple_strntoull(const char *cp, size_t max_chars, char **endp, unsigned int base) { unsigned long long result = 0ULL; const char *startp = cp; unsigned int rv; size_t chars;
cp = _parse_integer_fixup_radix(cp, &base); chars = cp - startp; if (chars >= max_chars) { /* We hit the limit */ cp = startp + max_chars; } else { rv = _parse_integer_limit(cp, base, &result, max_chars - chars); /* FIXME */ cp += (rv & ~KSTRTOX_OVERFLOW); }
if (endp) *endp = (char *)cp;
return result; }
...
+static long long simple_strntoll(const char *cp, size_t max_chars, char **endp,
unsigned int base)+{
- /*
* simple_strntoull safely handles receiving max_chars==0 in the* case we start with max_chars==1 and find a '-' prefix.
A nit-pick: Spaces surrounding '=='? simple_strntoull -> simple_strntoull()?
*/
Above misses to add something like:
"Otherwise we hit the '-' as an illegal number in the following simple_strntoull() call."
- if (*cp == '-' && max_chars > 0)
return -simple_strntoull(cp + 1, max_chars - 1, endp, base);- return simple_strntoull(cp, max_chars, endp, base);
+}
...
val.s = simple_strntoll(str,field_width > 0 ? field_width : SIZE_MAX,&next, base);
A nit-pick: Wouldn't be negative field_width "big enough" to just being used as is? Also, is field_width == 0 should be treated as "parse to the MAX"?
...
val.u = simple_strntoull(str,field_width > 0 ? field_width : SIZE_MAX,&next, base);
Ditto.