Re: [FFmpeg-devel] [PATCH 1/3] avcodec/wmavoice: Don't initialize GetBitContext with buf == NULL

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Andreas Rheinhardt:
> Happens when flushing. This triggers NULL + 0 (which is UB) in
> init_get_bits_xe (which previously errored out, but the return value
> has not been checked) and in copy_bits().
> 
> This fixes the wmavoice-(7|11|19)k FATE-tests with UBSan.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  libavcodec/wmavoice.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/libavcodec/wmavoice.c b/libavcodec/wmavoice.c
> index 4438089e51..26744719e6 100644
> --- a/libavcodec/wmavoice.c
> +++ b/libavcodec/wmavoice.c
> @@ -1900,6 +1900,8 @@ static int wmavoice_decode_packet(AVCodecContext *ctx, AVFrame *frame,
>  {
>      WMAVoiceContext *s = ctx->priv_data;
>      GetBitContext *gb = &s->gb;
> +    const uint8_t *buf = avpkt->data;
> +    uint8_t dummy[1];
>      int size, res, pos;
>  
>      /* Packets are sometimes a multiple of ctx->block_align, with a packet
> @@ -1908,7 +1910,8 @@ static int wmavoice_decode_packet(AVCodecContext *ctx, AVFrame *frame,
>       * in a single "muxer" packet, so we artificially emulate that by
>       * capping the packet size at ctx->block_align. */
>      for (size = avpkt->size; size > ctx->block_align; size -= ctx->block_align);
> -    init_get_bits8(&s->gb, avpkt->data, size);
> +    buf = size ? buf : dummy;
> +    init_get_bits8(&s->gb, buf, size);
>  
>      /* size == ctx->block_align is used to indicate whether we are dealing with
>       * a new packet or a packet of which we already read the packet header
> @@ -1931,7 +1934,7 @@ static int wmavoice_decode_packet(AVCodecContext *ctx, AVFrame *frame,
>              if (cnt + s->spillover_nbits > avpkt->size * 8) {
>                  s->spillover_nbits = avpkt->size * 8 - cnt;
>              }
> -            copy_bits(&s->pb, avpkt->data, size, gb, s->spillover_nbits);
> +            copy_bits(&s->pb, buf, size, gb, s->spillover_nbits);
>              flush_put_bits(&s->pb);
>              s->sframe_cache_size += s->spillover_nbits;
>              if ((res = synth_superframe(ctx, frame, got_frame_ptr)) == 0 &&
> @@ -1968,7 +1971,7 @@ static int wmavoice_decode_packet(AVCodecContext *ctx, AVFrame *frame,
>      } else if ((s->sframe_cache_size = pos) > 0) {
>          /* ... cache it for spillover in next packet */
>          init_put_bits(&s->pb, s->sframe_cache, SFRAME_CACHE_MAXSIZE);
> -        copy_bits(&s->pb, avpkt->data, size, gb, s->sframe_cache_size);
> +        copy_bits(&s->pb, buf, size, gb, s->sframe_cache_size);
>          // FIXME bad - just copy bytes as whole and add use the
>          // skip_bits_next field
>      }

Will apply this patchset tomorrow unless there are objections.

- Andreas

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