Re: [FFmpeg-devel] [PATCH 7/7] avcodec/cbs_jpeg: Try to move the read entity to one side in a test

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

Michael Niedermayer:
> Fixes: CID1439654 Untrusted pointer read
> 
> Sponsored-by: Sovereign Tech Fund
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/cbs_jpeg.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/cbs_jpeg.c b/libavcodec/cbs_jpeg.c
> index b1b58dcd65e..406147c082c 100644
> --- a/libavcodec/cbs_jpeg.c
> +++ b/libavcodec/cbs_jpeg.c
> @@ -146,13 +146,13 @@ static int cbs_jpeg_split_fragment(CodedBitstreamContext *ctx,
>              }
>          } else {
>              i = start;
> -            if (i + 2 > frag->data_size) {
> +            if (i > frag->data_size - 2) {
>                  av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid JPEG image: "
>                         "truncated at %02x marker.\n", marker);
>                  return AVERROR_INVALIDDATA;
>              }
>              length = AV_RB16(frag->data + i);
> -            if (i + length > frag->data_size) {
> +            if (length > frag->data_size - i) {
>                  av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid JPEG image: "
>                         "truncated at %02x marker segment.\n", marker);
>                  return AVERROR_INVALIDDATA;

You should always mention when you are not fixing bugs in our code, but
rather intend to apply workaround for coverity crazyness (i.e. the
requirement that reading values in non-native endianness needs to be
sanitized).

- Andreas

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