[FFmpeg-devel] [PATCH 5/7] avformat/wavdec: Avoid zeroing written to array

[Anton Khirnov]

Quoting Michael Niedermayer (2020-11-16 22:28:48)
> On Mon, Nov 16, 2020 at 07:07:21AM +0100, Anton Khirnov wrote:
> > Quoting Michael Niedermayer (2020-11-16 01:05:07)
> > > On Sat, Nov 14, 2020 at 11:12:15AM +0100, Anton Khirnov wrote:
> > > > Quoting Michael Niedermayer (2020-11-10 00:04:54)
> > > > > Fixes: OOM
> > > > > Fixes: 26934/clusterfuzz-testcase-minimized-ffmpeg_dem_W64_fuzzer-5996784213819392
> > > > > 
> > > > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > > > > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > > > > ---
> > > > >  libavformat/wavdec.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/libavformat/wavdec.c b/libavformat/wavdec.c
> > > > > index a81f2c7a67..6e5f4ccc12 100644
> > > > > --- a/libavformat/wavdec.c
> > > > > +++ b/libavformat/wavdec.c
> > > > > @@ -920,7 +920,7 @@ static int w64_read_header(AVFormatContext *s)
> > > > >                  if (chunk_size == UINT32_MAX || (filesize >= 0 && chunk_size > filesize))
> > > > >                      return AVERROR_INVALIDDATA;
> > > > >  
> > > > > -                value = av_mallocz(chunk_size + 1);
> > > > > +                value = av_malloc(chunk_size + 1);
> > > > 
> > > > This looks highly suspicious as a fix for anything other than
> > > > performance.
> > > 
> > > if iam not mistaken:
> > > The allocation doesnzt trigger OOM as no physical memory is allocated
> > > but once it is written to "z" it does and then OOMs
> > > if OTOH its written too while data is read from somewhere then a
> > > EOF ends writing and no OOM would happen
> > 
> > That is highly dependent on your OS and its configuration (e.g. you can
> > disable overcommit on Linux).
> 
> yes thats correct
> If the OS supports this then a OOM can be avoided, otherwise it will OOM
> Avoiding the OOM in the remaining cases seems too messy to me. OTOH
> this here is a rather simple change ...

I am okay with the change, I object to it being committed as a
(security) fix, since security fixes for platform-agnostic issues should
not be so highly platform-dependent.

Feel free to push if the commit message stops claiming it fixes OOM.


-- 
Anton Khirnov