Messages in this thread | | | Subject | Re: [PATCH v7 2/4] lib: vsprintf: Fix handling of number field widths in vsscanf | From | Richard Fitzgerald <> | Date | Mon, 29 Mar 2021 17:27:32 +0100 |
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On 29/03/2021 14:36, Andy Shevchenko wrote: > On Mon, Mar 29, 2021 at 01:08:22PM +0100, 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. >> >> Note that where a very large number is used to mean "unlimited", the value >> INT_MAX is used for consistency with the behaviour of vsnprintf(). > > ... > >> unsigned long simple_strtoul(const char *cp, char **endp, unsigned int base) >> { >> - return simple_strtoull(cp, endp, base); >> + return simple_strntoull(cp, INT_MAX, endp, base); > > Why do you need this change? >
I agree it's not necessary. I changed it between V1 and V2 but I can't remember what the reason was.
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