[FFmpeg-devel] [PATCH 1/2] avcodec/sanm: Check extradata_size before allocations

[Michael Niedermayer]

On Tue, Jul 16, 2019 at 08:27:43AM +0200, Reimar Döffinger wrote:
> On 16.07.2019, at 00:50, Michael Niedermayer <michael at niedermayer.cc> wrote:
> 
> > Fixes: Leaks
> > Fixes: 15349/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SANM_fuzzer-5102530557640704
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> > libavcodec/sanm.c | 9 ++++-----
> > 1 file changed, 4 insertions(+), 5 deletions(-)
> > 
> > diff --git a/libavcodec/sanm.c b/libavcodec/sanm.c
> > index 25aee7220f..60e2f4c624 100644
> > --- a/libavcodec/sanm.c
> > +++ b/libavcodec/sanm.c
> > @@ -491,6 +491,10 @@ static av_cold int decode_init(AVCodecContext *avctx)
> > 
> >     ctx->avctx   = avctx;
> >     ctx->version = !avctx->extradata_size;
> > +    if (!ctx->version && avctx->extradata_size < 1026) {
> > +        av_log(avctx, AV_LOG_ERROR, "Not enough extradata.\n");
> > +        return AVERROR_INVALIDDATA;
> > +    }
> > 
> >     avctx->pix_fmt = ctx->version ? AV_PIX_FMT_RGB565 : AV_PIX_FMT_PAL8;
> > 
> > @@ -506,11 +510,6 @@ static av_cold int decode_init(AVCodecContext *avctx)
> >     if (!ctx->version) {
> >         int i;
> > 
> > -        if (avctx->extradata_size < 1026) {
> > -            av_log(avctx, AV_LOG_ERROR, "Not enough extradata.\n");
> > -            return AVERROR_INVALIDDATA;
> > -        }
> 
> This seems quite a bit less obvious.

> Is that the only error return case, and is adding the cleanup code complex enough that this is the better choice?

there are 2 error cases, this one and a check for the allocations.
It seemd logic to me to do the check in the order of minimizing cleanup
but i can add the cleanup call if people prefer or do some other
solution ?


> Either way I'd recommend a comment like
> // early sanity check before allocations to avoid need for deallocation code.

will add

thanks

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many things microsoft did are stupid, but not doing something just because
microsoft did it is even more stupid. If everything ms did were stupid they
would be bankrupt already.
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