[FFmpeg-devel,1/2] avcodec/notchlc: Check uncompressed size against input for LZ4

Fixes: OOM
Fixes: 26168/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_NOTCHLC_fuzzer-6019839015256064

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/notchlc.c | 3 +++
 1 file changed, 3 insertions(+)

On Wed, Oct 14, 2020 at 05:53:07PM +0200, Michael Niedermayer wrote:
> Fixes: OOM
> Fixes: 26168/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_NOTCHLC_fuzzer-6019839015256064
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/notchlc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/libavcodec/notchlc.c b/libavcodec/notchlc.c
> index 3f7079da70..0254e7d76a 100644
> --- a/libavcodec/notchlc.c
> +++ b/libavcodec/notchlc.c
> @@ -490,6 +490,9 @@ static int decode_frame(AVCodecContext *avctx,
>  
>          bytestream2_init(gb, s->lzf_buffer, uncompressed_size);
>      } else if (s->format == 1) {
> +        if (bytestream2_get_bytes_left(gb) < uncompressed_size / 255)

From where you picked this division? And expecially 255 number?

> +            return AVERROR_INVALIDDATA;
> +
>          av_fast_padded_malloc(&s->uncompressed_buffer, &s->uncompressed_size,
>                                uncompressed_size);
>          if (!s->uncompressed_buffer)
> -- 
> 2.17.1
> 
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On Wed, Oct 14, 2020 at 07:54:34PM +0200, Paul B Mahol wrote:
> On Wed, Oct 14, 2020 at 05:53:07PM +0200, Michael Niedermayer wrote:
> > Fixes: OOM
> > Fixes: 26168/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_NOTCHLC_fuzzer-6019839015256064
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavcodec/notchlc.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/libavcodec/notchlc.c b/libavcodec/notchlc.c
> > index 3f7079da70..0254e7d76a 100644
> > --- a/libavcodec/notchlc.c
> > +++ b/libavcodec/notchlc.c
> > @@ -490,6 +490,9 @@ static int decode_frame(AVCodecContext *avctx,
> >  
> >          bytestream2_init(gb, s->lzf_buffer, uncompressed_size);
> >      } else if (s->format == 1) {
> > +        if (bytestream2_get_bytes_left(gb) < uncompressed_size / 255)
> 
> From where you picked this division? And expecially 255 number?

from a look at lz4_decompress(), it appeared to me that the amount
of bytes output is encoded so that each 255 bytes output require a byte
input. So the output would be bound to 255 times the input size
Did i miss something ?

thx

[...]

On Wed, Oct 14, 2020 at 09:17:40PM +0200, Michael Niedermayer wrote:
> On Wed, Oct 14, 2020 at 07:54:34PM +0200, Paul B Mahol wrote:
> > On Wed, Oct 14, 2020 at 05:53:07PM +0200, Michael Niedermayer wrote:
> > > Fixes: OOM
> > > Fixes: 26168/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_NOTCHLC_fuzzer-6019839015256064
> > > 
> > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > > ---
> > >  libavcodec/notchlc.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/libavcodec/notchlc.c b/libavcodec/notchlc.c
> > > index 3f7079da70..0254e7d76a 100644
> > > --- a/libavcodec/notchlc.c
> > > +++ b/libavcodec/notchlc.c
> > > @@ -490,6 +490,9 @@ static int decode_frame(AVCodecContext *avctx,
> > >  
> > >          bytestream2_init(gb, s->lzf_buffer, uncompressed_size);
> > >      } else if (s->format == 1) {
> > > +        if (bytestream2_get_bytes_left(gb) < uncompressed_size / 255)
> > 
> > From where you picked this division? And expecially 255 number?
> 
> from a look at lz4_decompress(), it appeared to me that the amount
> of bytes output is encoded so that each 255 bytes output require a byte
> input. So the output would be bound to 255 times the input size
> Did i miss something ?

#define LZ4_MAX_INPUT_SIZE        0x7E000000   /* 2 113 929 216 bytes */
#define LZ4_COMPRESSBOUND(isize)  ((unsigned)(isize) > (unsigned)LZ4_MAX_INPUT_SIZE ? 0 : (isize) + ((isize)/255) + 16)