On Wed, 10 May 2017 15:39:45 +0200 Michael Niedermayer <mich...@niedermayer.cc> wrote:
> On Wed, May 10, 2017 at 08:10:23AM -0400, Ronald S. Bultje wrote: > > Hi, > > > > On Tue, May 9, 2017 at 9:24 PM, Michael Niedermayer <mich...@niedermayer.cc> > > wrote: > > > > > On Tue, May 09, 2017 at 09:08:08PM -0400, Ronald S. Bultje wrote: > > > > Hi, > > > > > > > > On Tue, May 9, 2017 at 8:37 PM, Michael Niedermayer > > > <mich...@niedermayer.cc> > > > > wrote: > > > > > > > > > Fixes: out of array access > > > > > Fixes: 1434/clusterfuzz-testcase-minimized-6314998085189632 > > > > > Fixes: 1435/clusterfuzz-testcase-minimized-6483783723253760 > > > > > > > > > > Found-by: continuous fuzzing process https://github.com/google/oss- > > > > > fuzz/tree/master/targets/ffmpeg > > > > > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > > > > > --- > > > > > libavcodec/webp.c | 9 +++++++-- > > > > > 1 file changed, 7 insertions(+), 2 deletions(-) > > > > > > > > > > diff --git a/libavcodec/webp.c b/libavcodec/webp.c > > > > > index 16c3ae2662..23ed4bc26f 100644 > > > > > --- a/libavcodec/webp.c > > > > > +++ b/libavcodec/webp.c > > > > > @@ -1330,12 +1330,17 @@ static int vp8_lossy_decode_frame( > > > AVCodecContext > > > > > *avctx, AVFrame *p, > > > > > WebPContext *s = avctx->priv_data; > > > > > AVPacket pkt; > > > > > int ret; > > > > > + enum AVPixelFormat wanted_pix_fmt = s->has_alpha ? > > > > > AV_PIX_FMT_YUVA420P : AV_PIX_FMT_YUV420P; > > > > > + > > > > > + if (s->initialized && wanted_pix_fmt != avctx->pix_fmt) { > > > > > + ff_vp8_decode_free(avctx); > > > > > + s->initialized = 0; > > > > > + } > > > > > > > > > > if (!s->initialized) { > > > > > ff_vp8_decode_init(avctx); > > > > > s->initialized = 1; > > > > > - if (s->has_alpha) > > > > > - avctx->pix_fmt = AV_PIX_FMT_YUVA420P; > > > > > + avctx->pix_fmt = wanted_pix_fmt; > > > > > } > > > > > s->lossless = 0; > > > > > > > > > > > > What is the out of array access? webp is intra only and the only thing > > > that > > > > is initialized with memory in that call is reference frames. What's > > > > going > > > > on here? > > > > > > webp uses the same context as VP8, and it changes the pixel format > > > as it needs. Vp8 doesnt work if its format is changed under its feet > > > > > > I think what you're trying to say is that it doesn't work with RGBA as > > pixel format (it shouldn't need a reset between yuv420p and yuv420pa). We > > indeed don't set pix_fmt if has_alpha = 0, which seems like the core of the > > issue. I'm not sure you need to call ff_vp8_decode_init() twice, in fact > > I'm pretty sure you don't have to. It may also help to assert that pix_fmt > > is yuv420p(a) when calling vp8 functions. > > The reason why i replied privatly is because the details of security > issues should not be discussed in public before the fixes are available > in releases. As these details are usefull not only to us understanding > an issue but also to an attacker understanding and expoiting it > > Ill reply privatly again to awnser your questions Uh, just no. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
