On Sat, Mar 19, 2022 at 06:52:34PM +0100, Michael Niedermayer wrote: > On Fri, Mar 18, 2022 at 08:38:28AM -0300, James Almer wrote: > > > > > > On 3/18/2022 8:27 AM, Michael Niedermayer wrote: > > > On Thu, Mar 17, 2022 at 10:00:18PM -0300, James Almer wrote: > > > > > > > > > > > > On 3/17/2022 9:07 PM, James Almer wrote: > > > > > > > > > > > > > > > On 3/17/2022 8:52 PM, James Almer wrote: > > > > > > On 3/17/2022 8:30 PM, Michael Niedermayer wrote: > > > > > > > Fixes: Out of array write > > > > > > > Fixes: > > > > > > > 45613/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WMALOSSLESS_fuzzer-4539073606320128 > > > > > > > > > > > > > > > > > > > > > Found-by: continuous fuzzing process > > > > > > > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg > > > > > > > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > > > > > > > --- > > > > > > > libavcodec/wmalosslessdec.c | 3 +++ > > > > > > > 1 file changed, 3 insertions(+) > > > > > > > > > > > > > > diff --git a/libavcodec/wmalosslessdec.c > > > > > > > b/libavcodec/wmalosslessdec.c > > > > > > > index cd05b22689..1728920729 100644 > > > > > > > --- a/libavcodec/wmalosslessdec.c > > > > > > > +++ b/libavcodec/wmalosslessdec.c > > > > > > > @@ -281,6 +281,9 @@ static av_cold int > > > > > > > decode_init(AVCodecContext *avctx) > > > > > > > av_channel_layout_uninit(&avctx->ch_layout); > > > > > > > av_channel_layout_from_mask(&avctx->ch_layout, > > > > > > > channel_mask); > > > > > > > + if (s->num_channels != avctx->ch_layout.nb_channels) > > > > > > > + return AVERROR_PATCHWELCOME; //are there non fuzzed > > > > > > > files with this or is it an error ? > > > > > > > > > > > > s->num_channels at this point is set to the channels count the user > > > > > > set before calling avcodec_open2() (Normally from lavf), but it > > > > > > could be anything. > > > > > > If channel_mask is taken from extradata, maybe it should be used to > > > > > > set s->num_channels instead of aborting because the user set value > > > > > > and extradata disagreed. > > > > > > > > > > > > Also, can you reproduce this crash before 3c933af493? > > > > > > s->num_channels was being set to the user set channel count too, > > > > > > same as now. > > > > > > > > > > Right, before that commit s->num_channels and avctx->channels were > > > > > always the same, but avctx->channel_layout was whatever came from > > > > > extradata, and its popcnt could be != avctx->channels. > > > > > After it, avctx->ch_layout.nb_channels is always the same as > > > > > popcnt(avctx->ch_layout.u.mask), which can be different than > > > > > s->num_channels. > > > > > > > > > > I think my suggestion above to use the extradata channel mask and > > > > > ignoring the user set channel count is the best approach for this. > > > > > > > > Like this maybe (channel_mask could in theory be zero, so in that case > > > > the > > > > user set value should be used). > > > > > > > > > diff --git a/libavcodec/wmalosslessdec.c b/libavcodec/wmalosslessdec.c > > > > > index cd05b22689..915add1962 100644 > > > > > --- a/libavcodec/wmalosslessdec.c > > > > > +++ b/libavcodec/wmalosslessdec.c > > > > > @@ -197,15 +197,6 @@ static av_cold int decode_init(AVCodecContext > > > > > *avctx) > > > > > return AVERROR_PATCHWELCOME; > > > > > } > > > > > > > > > > - s->max_frame_size = MAX_FRAMESIZE * avctx->ch_layout.nb_channels; > > > > > - s->frame_data = av_mallocz(s->max_frame_size + > > > > > AV_INPUT_BUFFER_PADDING_SIZE); > > > > > - if (!s->frame_data) > > > > > - return AVERROR(ENOMEM); > > > > > - > > > > > - s->avctx = avctx; > > > > > - ff_llauddsp_init(&s->dsp); > > > > > - init_put_bits(&s->pb, s->frame_data, s->max_frame_size); > > > > > - > > > > > if (avctx->extradata_size >= 18) { > > > > > s->decode_flags = AV_RL16(edata_ptr + 14); > > > > > channel_mask = AV_RL32(edata_ptr + 2); > > > > > @@ -230,6 +221,33 @@ static av_cold int decode_init(AVCodecContext > > > > > *avctx) > > > > > return AVERROR_PATCHWELCOME; > > > > > } > > > > > > > > > > + if (channel_mask) { > > > > > + av_channel_layout_uninit(&avctx->ch_layout); > > > > > + av_channel_layout_from_mask(&avctx->ch_layout, channel_mask); > > > > > + } else > > > > > + avctx->ch_layout.order = AV_CHANNEL_ORDER_UNSPEC; > > > > > + > > > > > + s->num_channels = avctx->ch_layout.nb_channels; > > > > > + > > > > > + /* extract lfe channel position */ > > > > > + s->lfe_channel = -1; > > > > > + > > > > > + if (channel_mask & 8) { > > > > > + unsigned int mask; > > > > > + for (mask = 1; mask < 16; mask <<= 1) > > > > > + if (channel_mask & mask) > > > > > + ++s->lfe_channel; > > > > > + } > > > > > + > > > > > + s->max_frame_size = MAX_FRAMESIZE * avctx->ch_layout.nb_channels; > > > > > + s->frame_data = av_mallocz(s->max_frame_size + > > > > > AV_INPUT_BUFFER_PADDING_SIZE); > > > > > + if (!s->frame_data) > > > > > + return AVERROR(ENOMEM); > > > > > + > > > > > + s->avctx = avctx; > > > > > + ff_llauddsp_init(&s->dsp); > > > > > + init_put_bits(&s->pb, s->frame_data, s->max_frame_size); > > > > > + > > > > > /* generic init */ > > > > > s->log2_frame_size = av_log2(avctx->block_align) + 4; > > > > > > > > > > @@ -263,24 +281,10 @@ static av_cold int decode_init(AVCodecContext > > > > > *avctx) > > > > > return AVERROR_INVALIDDATA; > > > > > } > > > > > > > > > > - s->num_channels = avctx->ch_layout.nb_channels; > > > > > - > > > > > - /* extract lfe channel position */ > > > > > - s->lfe_channel = -1; > > > > > - > > > > > - if (channel_mask & 8) { > > > > > - unsigned int mask; > > > > > - for (mask = 1; mask < 16; mask <<= 1) > > > > > - if (channel_mask & mask) > > > > > - ++s->lfe_channel; > > > > > - } > > > > > - > > > > > s->frame = av_frame_alloc(); > > > > > if (!s->frame) > > > > > return AVERROR(ENOMEM); > > > > > > > > > > - av_channel_layout_uninit(&avctx->ch_layout); > > > > > - av_channel_layout_from_mask(&avctx->ch_layout, channel_mask); > > > > > return 0; > > > > > } > > > > > > this will change the output of the "lossless" decoder if this case ever > > > occurs besides this > > > > As i interpret it, you could initialize the decoder using any arbitrary > > number of channels in avctx. And if channel_mask in extradata is not zero, > > then it must be considered to be the valid channel count for the stream, and > > the value passed in avctx should be ignored. > > without a specification and no non fuzzed testfile its really not possible > to say for sure what this combination is intended to produce on the output > > What you say sounds reasonable but it can also be something else
ping, i think your patch or something similar should be applied The fuzzer found 46008/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WMALOSSLESS_fuzzer-4681245747970048 which too crashes because of the channel number thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB If you fake or manipulate statistics in a paper in physics you will never get a job again. If you fake or manipulate statistics in a paper in medicin you will get a job for life at the pharma industry.
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