[FFmpeg-devel] [PATCH] avcodec/cbs_h265: don't attempt to read 0 length elements in sei_3d_reference_displays_info

[FFmpeg-devel] [PATCH] avcodec/cbs_h265: don't attempt to read 0 length elements in sei_3d_reference_displays_info

[James Almer]

Fixes: 70458/clusterfuzz-testcase-minimized-ffmpeg_BSF_TRACE_HEADERS_fuzzer-5259339779080192
Fixes: Assertion width > 0 && width <= 32 failed at libavcodec/cbs.c:608

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: James Almer <jamrial@gmail.com>
---
 libavcodec/cbs_h265_syntax_template.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/libavcodec/cbs_h265_syntax_template.c b/libavcodec/cbs_h265_syntax_template.c
index f1be30a6c9..12fa185c77 100644
--- a/libavcodec/cbs_h265_syntax_template.c
+++ b/libavcodec/cbs_h265_syntax_template.c
@@ -2307,7 +2307,10 @@ SEI_FUNC(sei_3d_reference_displays_info, (CodedBitstreamContext *ctx, RWContext
         else
             length = FFMAX(0, (int)current->exponent_ref_display_width[i] +
                               (int)current->prec_ref_display_width - 31);
-        ubs(length, mantissa_ref_display_width[i], 1, i);
+        if (length)
+            ubs(length, mantissa_ref_display_width[i], 1, i);
+        else
+            infer(mantissa_ref_display_width[i], 0);
         if (current->ref_viewing_distance_flag) {
             us(6, exponent_ref_viewing_distance[i], 0, 62, 1, i);
             if (!current->exponent_ref_viewing_distance[i])
@@ -2315,7 +2318,10 @@ SEI_FUNC(sei_3d_reference_displays_info, (CodedBitstreamContext *ctx, RWContext
             else
                 length = FFMAX(0, (int)current->exponent_ref_viewing_distance[i] +
                                   (int)current->prec_ref_viewing_dist - 31);
-            ubs(length, mantissa_ref_viewing_distance[i], 1, i);
+            if (length)
+                ubs(length, mantissa_ref_viewing_distance[i], 1, i);
+            else
+                infer(mantissa_ref_viewing_distance[i], 0);
         }
         flags(additional_shift_present_flag[i], 1, i);
         if (current->additional_shift_present_flag[i])
-- 
2.45.2

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Re: [FFmpeg-devel] [PATCH] avcodec/cbs_h265: don't attempt to read 0 length elements in sei_3d_reference_displays_info

[James Almer]

On 8/1/2024 1:18 PM, James Almer wrote:
> Fixes: 70458/clusterfuzz-testcase-minimized-ffmpeg_BSF_TRACE_HEADERS_fuzzer-5259339779080192
> Fixes: Assertion width > 0 && width <= 32 failed at libavcodec/cbs.c:608
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
>   libavcodec/cbs_h265_syntax_template.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/cbs_h265_syntax_template.c b/libavcodec/cbs_h265_syntax_template.c
> index f1be30a6c9..12fa185c77 100644
> --- a/libavcodec/cbs_h265_syntax_template.c
> +++ b/libavcodec/cbs_h265_syntax_template.c
> @@ -2307,7 +2307,10 @@ SEI_FUNC(sei_3d_reference_displays_info, (CodedBitstreamContext *ctx, RWContext
>           else
>               length = FFMAX(0, (int)current->exponent_ref_display_width[i] +
>                                 (int)current->prec_ref_display_width - 31);
> -        ubs(length, mantissa_ref_display_width[i], 1, i);
> +        if (length)
> +            ubs(length, mantissa_ref_display_width[i], 1, i);
> +        else
> +            infer(mantissa_ref_display_width[i], 0);
>           if (current->ref_viewing_distance_flag) {
>               us(6, exponent_ref_viewing_distance[i], 0, 62, 1, i);
>               if (!current->exponent_ref_viewing_distance[i])
> @@ -2315,7 +2318,10 @@ SEI_FUNC(sei_3d_reference_displays_info, (CodedBitstreamContext *ctx, RWContext
>               else
>                   length = FFMAX(0, (int)current->exponent_ref_viewing_distance[i] +
>                                     (int)current->prec_ref_viewing_dist - 31);
> -            ubs(length, mantissa_ref_viewing_distance[i], 1, i);
> +            if (length)
> +                ubs(length, mantissa_ref_viewing_distance[i], 1, i);
> +            else
> +                infer(mantissa_ref_viewing_distance[i], 0);
>           }
>           flags(additional_shift_present_flag[i], 1, i);
>           if (current->additional_shift_present_flag[i])

Applied.
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