[PATCH v2 3/3] git_parse_signed(): avoid integer overflow
- From
- Phillip Wood via GitGitGadget <gitgitgadget@gmail.com>
- Date
- Nov 9, 2022, 14:16 UTC
- Message-ID
- <673e6f1ab93200ab3b6b9ca2bded5db5a3274329.1668003388.git.gitgitgadget@gmail.com>
- In-Reply-To
- <pull.1389.v2.git.1668003388.gitgitgadget@gmail.com>
From: Phillip Wood <phillip.wood@dunelm.org.uk>
git_parse_signed() checks that the absolute value of the parsed string is less than or equal to a caller supplied maximum value. When calculating the absolute value there is a integer overflow if `val == INTMAX_MIN`. To fix this avoid negating `val` when it is negative by having separate overflow checks for positive and negative values.
An alternative would be to special case INTMAX_MIN before negating `val` as it is always out of range. That would enable us to keep the existing code but I'm not sure that the current two-stage check is any clearer than the new version.
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk> --- config.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/config.c b/config.c index b7fb68026d8..aad3e00341d 100644 --- a/config.c +++ b/config.c @@ -1160,8 +1160,10 @@ static int git_parse_signed(const char *value, intmax_t *ret, intmax_t max) if (value && *value) { char *end; intmax_t val; - uintmax_t uval; - uintmax_t factor; + intmax_t factor; + + if (max < 0) + BUG("max must be a positive integer"); errno = 0; val = strtoimax(value, &end, 0); @@ -1176,9 +1178,8 @@ static int git_parse_signed(const char *value, intmax_t *ret, intmax_t max) errno = EINVAL; return 0; } - uval = val < 0 ? -val : val; - if (unsigned_mult_overflows(factor, uval) || - factor * uval > max) { + if ((val < 0 && -max / factor > val) || + (val > 0 && max / factor < val)) { errno = ERANGE; return 0; }
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