James Almer:
On 10/2/2022 1:13 PM, Rémi Denis-Courmont wrote:
Le sunnuntaina 2. lokakuuta 2022, 18.43.23 EEST Michael Niedermayer a écrit :
Fixes: signed integer overflow: 2040812214 + 255101526 cannot be represented in type 'int' Fixes: 51323/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_BONK_fuzzer-4791481 067503616
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- libavcodec/bonk.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/libavcodec/bonk.c b/libavcodec/bonk.c index 409694f710d..32f7c9b9bdb 100644 --- a/libavcodec/bonk.c +++ b/libavcodec/bonk.c @@ -187,6 +187,9 @@ static int intlist_read(BonkContext *s, int *buf, int entries, int base_2_part) if (!dominant) n_zeros += steplet;
+ if (step > INT_MAX/9*8) + return AVERROR_INVALIDDATA; + step += step / 8; } else if (steplet > 0) { int actual_run = read_uint_max(s, steplet - 1);
No problem with this patch *specifically* but wouldn't it be more effective to fix that sort of issue with checked arithmetic, e.g. something like:
if (av_ckd_add(&step, step, step / 8))
That's __builtin_add_overflow() from gcc/clang.
There's av_sat_add32(), which will clip the result to fit in a 32-bit variable. So i guess it could be used and then just check for step == INT32_MAX and error out, but that's slower than what this patch is doing.
The result of av_sat_add32() being INT32_MAX/MIN does not imply that the result has been saturated. Apart from that, the documentation of av_sat_add32() pretty much presumes that INT_MIN/MAX == INT32_MIN/MAX.
return AVERROR_INVALIDDATA;
...especially on 64-bit systems whence this is really just an add. This also avoids having to figure out what the exact boundary value is.
What 64-bit arch has sizeof(int) == 8?
IIRC on Cray computers all integer types that don't have a size of 1 (character types) have size 8. Notice that there are several places in our codebase where we pretty much presume int/unsigned to be 32bits (and to have no padding). - Andreas