In '_parse_integer_limit()', adjust native integer arithmetic with near-to-overflow branch where 'check_mul_overflow()' and 'check_add_overflow()' are used to check whether an intermediate result goes out of range, and denote such a case with ULLONG_MAX, thus making the function more similar to standard C library's 'strtoull()'. Adjust comment to kernel-doc style as well.
Signed-off-by: Dmitry Antipov <[email protected]> --- v4: restore plain integer arithmetic and use check_xxx_overflow() on near-to-overflow branch only v3: adjust commit message and comments as suggested by Andy v2: initial version to join the series --- lib/kstrtox.c | 38 +++++++++++++++++++++++++------------- 1 file changed, 25 insertions(+), 13 deletions(-) diff --git a/lib/kstrtox.c b/lib/kstrtox.c index bdde40cd69d7..137132e1a207 100644 --- a/lib/kstrtox.c +++ b/lib/kstrtox.c @@ -39,20 +39,26 @@ const char *_parse_integer_fixup_radix(const char *s, unsigned int *base) return s; } -/* - * Convert non-negative integer string representation in explicitly given radix - * to an integer. A maximum of max_chars characters will be converted. +/** + * _parse_integer_limit - Convert integer string representation to an integer + * @s: Integer string representation + * @base: Radix + * @p: Where to store result + * @max_chars: Maximum amount of characters to convert + * + * Convert non-negative integer string representation in explicitly given + * radix to an integer. If overflow occurs, value at @p is set to ULLONG_MAX. * - * Return number of characters consumed maybe or-ed with overflow bit. - * If overflow occurs, result integer (incorrect) is still returned. + * This function is the workhorse of other string conversion functions and it + * is discouraged to use it explicitly. Consider kstrto*() family instead. * - * Don't you dare use this function. + * Return: Number of characters consumed, maybe ORed with overflow bit */ noinline unsigned int _parse_integer_limit(const char *s, unsigned int base, unsigned long long *p, size_t max_chars) { - unsigned long long res; + unsigned long long tmp, res; unsigned int rv; res = 0; @@ -72,14 +78,20 @@ unsigned int _parse_integer_limit(const char *s, unsigned int base, unsigned lon if (val >= base) break; /* - * Check for overflow only if we are within range of - * it in the max base we support (16) + * Accumulate result if no overflow detected. + * Otherwise just consume valid characters. */ - if (unlikely(res & (~0ull << 60))) { - if (res > div_u64(ULLONG_MAX - val, base)) - rv |= KSTRTOX_OVERFLOW; + if (likely(res != ULLONG_MAX)) { + if (unlikely(res & (~0ull << 60))) { + /* We're close to possible overflow. */ + if (check_mul_overflow(res, base, &tmp) || + check_add_overflow(tmp, val, &res)) { + res = ULLONG_MAX; + rv |= KSTRTOX_OVERFLOW; + } + } else + res = res * base + val; } - res = res * base + val; rv++; s++; } -- 2.52.0
