On Sun, 2020-11-08 at 15:13 +0100, Michael Niedermayer wrote: > CAUTION: This email originated from outside of the organization. Do not click > links or open attachments unless you recognize the sender and know the > content is safe. > > > On Sun, Nov 08, 2020 at 11:35:43AM +0100, Andreas Rheinhardt wrote: > > Michael Niedermayer: > > > On Fri, Oct 16, 2020 at 10:57:22AM +0200, Joakim Tjernlund wrote: > > > > From > > > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugs.chromium.org%2Fp%2Fchromium%2Fissues%2Fdetail%3Fid%3D1095962&data=04%7C01%7Cjoakim.tjernlund%40infinera.com%7C0c52cb182fa941b874c908d883f07c2c%7C285643de5f5b4b03a1530ae2dc8aaf77%7C1%7C0%7C637404416183627186%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=7wEFER5KUD1KEnTJ7mr2xnfmOzctpDsb0Bld%2BfAvjAc%3D&reserved=0 > > > > ---------------------------- > > > > This seems to be caused by the custom handling of "av_max_alloc(0)" in > > > > Chromium's ffmpeg fork to mean unlimited (added in [1]). > > > > > > > > Upstream ffmpeg doesn't treat 0 as a special value; versions before 4.3 > > > > seemingly worked > > > > because 32 was subtracted from max_alloc_size (set to 0 by Chromium) > > > > resulting in an > > > > integer underflow, making the effective limit be SIZE_MAX - 31. > > > > > > > > Now that the above underflow doesn't happen, the tab just crashes. The > > > > upstream change > > > > for no longer subtracting 32 from max_alloc_size was included in ffmpeg > > > > 4.3. [2] > > > > > > > > [1] > > > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fchromium-review.googlesource.com%2Fc%2Fchromium%2Fthird_party%2Fffmpeg%2F%2B%2F73563&data=04%7C01%7Cjoakim.tjernlund%40infinera.com%7C0c52cb182fa941b874c908d883f07c2c%7C285643de5f5b4b03a1530ae2dc8aaf77%7C1%7C0%7C637404416183627186%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=s%2BnujuFPv6QwNlIKjuXQNcDR3wvA%2BY7Uu4Qnr%2FsHjnE%3D&reserved=0 > > > > [2] > > > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FFFmpeg%2FFFmpeg%2Fcommit%2F731c77589841&data=04%7C01%7Cjoakim.tjernlund%40infinera.com%7C0c52cb182fa941b874c908d883f07c2c%7C285643de5f5b4b03a1530ae2dc8aaf77%7C1%7C0%7C637404416183637145%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ftg9ysBzC5YD9uEe%2BgJwZIecW8a6fAXXNS9kGqDMnp8%3D&reserved=0 > > > > --------------------------- > > > > > > > > Restore av_malloc_max(0) to MAX_INT fixing MS Teams, Discord older > > > > chromium etc. > > > > > > > > Signed-off-by: Joakim Tjernlund <joakim.tjernl...@infinera.com> > > > > --- > > > > > > > > v2: Cover the full API range 0-31 > > > > > > > > v3: Closer compat with < 4.3 ffmpeg > > > > > > > > v4: Adjust size accoriding to Andreas Rheinhardt comments > > > > > > > > libavutil/mem.c | 2 ++ > > > > 1 file changed, 2 insertions(+) > > > > > > "Unbreak av_malloc_max(0) API/ABI" > > > The commit message of this is incorrect > > > > > > The API before and after this documented the current git master behavior > > > more correct would be > > > "Break API of av_malloc_max() for 0-31, to restore ABI behavior so > > > applications using this do not need to be changed" > > > > > > > I agree. > > > > > Also id like to raise awareness that this function had a big warning: > > > * > > > * @warning Exercise extreme caution when using this function. Don't > > > touch > > > * this if you do not understand the full consequence of > > > doing so. > > > */ > > > void av_max_alloc(size_t max); > > > > > > And also id like to raise awareness that the default limit is INT_MAX > > > while with 0 as argument it becomes SIZE_MAX. > > > > No: With the old version 0 was effectively SIZE_MAX - 31, with current > > git head 0 means that all allocations of > 0 fail (yet requests of size > > 0 still result in an allocation of size 1); with the proposed version > > av_max_alloc(0) would set the limit to SIZE_MAX - 32. This off-by-one is > > surely unintentional. > > > > > I would expect that is > > > not safe everywhere and could open security issues. > > > If anything 0 should be interpreted as the default INT_MAX > > > > That would be an API break. > > yes, that was meant as a "less bad" alternative to SIZE_MAX - 31 > > > > > > > If its not obvious where SIZE_MAX can be an issue, consider what we > > > use to index arrays, int, and that doesnt go to SIZE_MAX but instead > > > hits undefined behavior maybe becomes negative and accesses out of array > > > > Any code that relies on allocations > INT_MAX to fail is buggy and must > > be fixed; > > YES > > > > and so is any code that uses an index parameter of type int > > and uses a comparison with a value of type size_t as its loop condition. > > YES > though there are more complex failure cases > for example a > array[i + j*C] > here the 2 loops for i and j can have int limits and int indexes and still > if the array is not limited to INT_MAX this could go bad > > > > > > - Andreas > > > > *: Btw: AVFormatContext.nb_streams is unsigned, yet it is common to use > > an int to loop over the streams. This is not dangerous now, as the > > max_streams option is limited to INT_MAX. But we should probably change > > this habit. > > yes > > thx
Did you reach a conclusion ? Go back to my original patch ? Jocke _______________________________________________ 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".