linux/lib/kstrtox.h
Richard Fitzgerald 900fdc4573 lib: vsprintf: Fix handling of number field widths in vsscanf
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().

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210514161206.30821-2-rf@opensource.cirrus.com
2021-05-19 15:05:11 +02:00

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C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LIB_KSTRTOX_H
#define _LIB_KSTRTOX_H
#define KSTRTOX_OVERFLOW (1U << 31)
const char *_parse_integer_fixup_radix(const char *s, unsigned int *base);
unsigned int _parse_integer_limit(const char *s, unsigned int base, unsigned long long *res,
size_t max_chars);
unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long *res);
#endif