Re: [FFmpeg-devel] [h264] Make ff_h264_build_ref_list stricter with AV_EF_EXPLODE

[Michael Niedermayer <michael@niedermayer.cc>]

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Hi

On Tue, Aug 05, 2025 at 02:52:28PM -0700, Dale Curtis wrote:
> Don't silently skip errors when AV_EF_EXPLODE is specified. This can
> lead to out-of-bound reads with ff_put_h264_chroma_mc4_ssse3() when
> small padding is used with the checked bitstream reader.
> 
> Signed-off-by: Dale Curtis <dalecurtis@chromium.org>

>  h264_refs.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> e453856d1d24c3a4c2e42d61acdeff3b09b226da  h264_stricter_v1.patch
> From 46b2fa1ec0cbd00c4fd3909665608d79760654d0 Mon Sep 17 00:00:00 2001
> From: Dale Curtis <dalecurtis@chromium.org>
> Date: Tue, 5 Aug 2025 21:45:19 +0000
> Subject: [PATCH] Make ff_h264_build_ref_list stricter with AV_EF_EXPLODE
> 

> Don't silently skip errors when AV_EF_EXPLODE is specified.

ok


> This can
> lead to out-of-bound reads with ff_put_h264_chroma_mc4_ssse3() when
> small padding is used with the checked bitstream reader.

this sounds a bit fishy


> 
> Signed-off-by: Dale Curtis <dalecurtis@chromium.org>
> ---
>  libavcodec/h264_refs.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/libavcodec/h264_refs.c b/libavcodec/h264_refs.c
> index 74840e5909..e6e3adf502 100644
> --- a/libavcodec/h264_refs.c
> +++ b/libavcodec/h264_refs.c
> @@ -370,6 +370,9 @@ int ff_h264_build_ref_list(H264Context *h, H264SliceContext *sl)
>                         i < 0 ? "reference picture missing during reorder\n" :
>                                 "mismatching reference\n"
>                        );
> +                if (h->avctx->err_recognition & AV_EF_EXPLODE) {
> +                  return AVERROR_INVALIDDATA;
> +                }

indention depth is 4 in ffmpeg consistently


>                  memset(&sl->ref_list[list][index], 0, sizeof(sl->ref_list[0][0])); // FIXME
>              } else {
>                  for (i = index; i + 1 < sl->ref_count[list]; i++) {
> @@ -392,6 +395,10 @@ int ff_h264_build_ref_list(H264Context *h, H264SliceContext *sl)
>          for (int index = 0; index < sl->ref_count[list]; index++) {
>              if (   !sl->ref_list[list][index].parent
>                  || (!FIELD_PICTURE(h) && (sl->ref_list[list][index].reference&3) != 3)) {
> +                if (h->avctx->err_recognition & AV_EF_EXPLODE) {
> +                  av_log(h->avctx, AV_LOG_ERROR, "Missing reference picture\n");
> +                  return AVERROR_INVALIDDATA;
> +                }
>                  av_log(h->avctx, AV_LOG_ERROR, "Missing reference picture, default is %d\n", h->default_ref[list].poc);

the error out can be after this av_log() avoiding the 2nd av_log() in the if()

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I am the wisest man alive, for I know one thing, and that is that I know
nothing. -- Socrates

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