[PATCH] avcodec/bonk: Check step
Fixes: signed integer overflow: 2040812214 + 255101526 cannot be represented in type 'int' Fixes: 51323/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_BONK_fuzzer-4791481067503616 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); -- 2.17.1
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)) 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. -- レミ・デニ-クールモン http://www.remlab.net/
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.
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?
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
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 <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.
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/
On Sun, Oct 02, 2022 at 07:13:39PM +0300, 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)
if you want the exact limit for any INT_MAX its: (INT_MAX + 1ULL) / 9 * 8 + (INT_MAX + 1ULL) % 9 - 1; though probably a fixed bit value would be better anyway for reproducability
+ 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)) 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.
If someone has a set of testfiles for this decoder then I can look at this and cleanup the code more completely. i dont know if a step > C vs overflow check is better but i have the suspicion there are more problems as multiple statments around this seem unreachable. And iam also missing some check that i would expect to be in there I found links to datafilehost.com to test files but they are all expired so i have no test files, so iam a bit cautious with changes ... CCing piotr who linked to the files on datafilehost, maybe he still has them. thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB In fact, the RIAA has been known to suggest that students drop out of college or go to community college in order to be able to afford settlements. -- The RIAA
participants (4)
-
Andreas Rheinhardt -
James Almer -
Michael Niedermayer -
Rémi Denis-Courmont