Le sunnuntaina 2. lokakuuta 2022, 19.26.21 EEST James Almer a écrit : > 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-47914 > >> 81 > >> 067503616 > >> > >> Found-by: continuous fuzzing process > >> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg > >> Signed-off-by: Michael Niedermayer <mich...@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.
I took the name and paramater order ckd_add from Cnext's <stdckdint.h>. > 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. Yes but the saturation behaviour is what makes it slower, and it's totally unnecessary here. On x86-64, GCC generates this for Michael's code: cmp $0x71c71c70,%edi jg 1f test %edi,%edi lea 0x7(%rdi),%eax cmovns %edi,%eax sar $0x3,%eax add %edi,%eax ret 1: cs nopw 0x0(%rax,%rax,1) mov $0xffffffea,%eax ret cs nopw 0x0(%rax,%rax,1) And this if you use checked overflowing arithmetic: test %edi,%edi lea 0x7(%rdi),%eax mov $0xffffffea,%edx cmovns %edi,%eax sar $0x3,%eax add %edi,%eax cmovo %edx,%eax ret > > 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? None. But the compiler can freely upgrade the addition to 64-bit internally. -- 雷米‧德尼-库尔蒙 http://www.remlab.net/ _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".