Re: [FFmpeg-devel] [PATCH] libswresample: Prevent out of bounds.

["Ronald S. Bultje" <rsbultje@gmail.com>]

Hi,

On Wed, Aug 2, 2023 at 7:31 AM kobrineli <kobrineli@ispras.ru> wrote:

> From: Eli Kobrin <kobrineli@ispras.ru>
>
> We've been fuzzing torchvision with [sydr-fuzz](
> https://github.com/ispras/oss-sydr-fuzz)
> and found out of bounds error in ffmpeg project at audioconvert.c:51.
> To prevent error we need to insert corresponding check and fix checks
> for in and out fmt in swr_init.
>
> Signed-off-by: Eli Kobrin <kobrineli@ispras.ru>
> ---
>  libswresample/audioconvert.c | 7 ++++++-
>  libswresample/swresample.c   | 4 ++--
>  2 files changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/libswresample/audioconvert.c b/libswresample/audioconvert.c
> index 1d75ba1495..701f4808a0 100644
> --- a/libswresample/audioconvert.c
> +++ b/libswresample/audioconvert.c
> @@ -148,7 +148,12 @@ AudioConvert *swri_audio_convert_alloc(enum
> AVSampleFormat out_fmt,
>                                         int flags)
>  {
>      AudioConvert *ctx;
> -    conv_func_type *f =
> fmt_pair_to_conv_functions[av_get_packed_sample_fmt(out_fmt) +
> AV_SAMPLE_FMT_NB*av_get_packed_sample_fmt(in_fmt)];
> +
> +    size_t idx = av_get_packed_sample_fmt(out_fmt) + AV_SAMPLE_FMT_NB *
> av_get_packed_sample_fmt(in_fmt);
> +    if (idx >= AV_SAMPLE_FMT_NB * AV_SAMPLE_FMT_NB)
> +        return NULL;
> +
> +    conv_func_type *f = fmt_pair_to_conv_functions[idx];
>

This is not necessary anymore, please remove this portion.


> diff --git a/libswresample/swresample.c b/libswresample/swresample.c
> index 6dc329a9d0..b7cab36710 100644
> --- a/libswresample/swresample.c
> +++ b/libswresample/swresample.c
> @@ -196,11 +196,11 @@ av_cold int swr_init(struct SwrContext *s){
>
>      clear_context(s);
>
> -    if(s-> in_sample_fmt >= AV_SAMPLE_FMT_NB){
> +    if(s-> in_sample_fmt >= AV_SAMPLE_FMT_NB || s-> in_sample_fmt < 0){
>          av_log(s, AV_LOG_ERROR, "Requested input sample format %d is
> invalid\n", s->in_sample_fmt);
>          return AVERROR(EINVAL);
>      }
> -    if(s->out_sample_fmt >= AV_SAMPLE_FMT_NB){
> +    if(s->out_sample_fmt >= AV_SAMPLE_FMT_NB || s->out_sample_fmt < 0){
>          av_log(s, AV_LOG_ERROR, "Requested output sample format %d is
> invalid\n", s->out_sample_fmt);
>          return AVERROR(EINVAL);
>      }
> --
> 2.25.1
>

You can simplify this to "if ((unsigned) s->in/out_sample_fmt >=
AV_SAMPLE_FMT_NB)".

Ronald
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