Commit 5a23ac8460 for ffmpeg

commit 5a23ac8460a7bc1c2cdbf6ac62bd67e023451b8f
Author: Michael Niedermayer <michael@niedermayer.cc>
Date:   Thu Sep 24 00:44:30 2026 +0200

    avcodec/hevc: reject an alpha layer frame without a base layer frame

    Fixes: NULL pointer dereference
    Fixes: 70rhPmst9XNe
    Fixes: hevc_alpha_null.hevc
    Replicated through UnModified FFmpeg
    Regression since: f926b60455
    Found-by: Glops Elemiu

diff --git a/libavcodec/hevc/hevcdec.c b/libavcodec/hevc/hevcdec.c
index 9bbe6fe5a5..6f65dd5af9 100644
--- a/libavcodec/hevc/hevcdec.c
+++ b/libavcodec/hevc/hevcdec.c
@@ -3266,6 +3266,11 @@ static int hevc_frame_start(HEVCContext *s, HEVCLayerContext *l,
         return AVERROR_INVALIDDATA;
     }

+    if (l != &s->layers[0] && ff_hevc_is_alpha_video(s) && !s->layers[0].cur_frame) {
+        av_log(s->avctx, AV_LOG_ERROR, "Alpha layer frame without a base layer frame\n");
+        return AVERROR_INVALIDDATA;
+    }
+
     av_refstruct_replace(&s->pps, pps);
     if (l->sps != sps) {
         const HEVCSPS *sps_base = s->layers[0].sps;