avcodec/decode: Consider discarded samples in max_samples

Fixes: Timeout (several minutes -> 3 sec)
Fixes: 25246/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5943400661254144

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/decode.c

@@ -318,7 +318,7 @@ static int64_t guess_correct_pts(AVCodecContext *ctx,
  * returning any output, so this function needs to be called in a loop until it
  * returns EAGAIN.
  **/
-static inline int decode_simple_internal(AVCodecContext *avctx, AVFrame *frame)
+static inline int decode_simple_internal(AVCodecContext *avctx, AVFrame *frame, int64_t *discarded_samples)
 {
     AVCodecInternal   *avci = avctx->internal;
     DecodeSimpleContext *ds = &avci->ds;
@@ -411,12 +411,14 @@ static inline int decode_simple_internal(AVCodecContext *avctx, AVFrame *frame)
             !(avctx->flags2 & AV_CODEC_FLAG2_SKIP_MANUAL)) {
             avci->skip_samples = FFMAX(0, avci->skip_samples - frame->nb_samples);
             got_frame = 0;
+            *discarded_samples += frame->nb_samples;
         }
 
         if (avci->skip_samples > 0 && got_frame &&
             !(avctx->flags2 & AV_CODEC_FLAG2_SKIP_MANUAL)) {
             if(frame->nb_samples <= avci->skip_samples){
                 got_frame = 0;
+                *discarded_samples += frame->nb_samples;
                 avci->skip_samples -= frame->nb_samples;
                 av_log(avctx, AV_LOG_DEBUG, "skip whole frame, skip left: %d\n",
                        avci->skip_samples);
@@ -444,6 +446,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
                 }
                 av_log(avctx, AV_LOG_DEBUG, "skip %d/%d samples\n",
                        avci->skip_samples, frame->nb_samples);
+                *discarded_samples += avci->skip_samples;
                 frame->nb_samples -= avci->skip_samples;
                 avci->skip_samples = 0;
             }
@@ -452,6 +455,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
         if (discard_padding > 0 && discard_padding <= frame->nb_samples && got_frame &&
             !(avctx->flags2 & AV_CODEC_FLAG2_SKIP_MANUAL)) {
             if (discard_padding == frame->nb_samples) {
+                *discarded_samples += frame->nb_samples;
                 got_frame = 0;
             } else {
                 if(avctx->pkt_timebase.num && avctx->sample_rate) {
@@ -544,9 +548,12 @@ FF_ENABLE_DEPRECATION_WARNINGS
 static int decode_simple_receive_frame(AVCodecContext *avctx, AVFrame *frame)
 {
     int ret;
+    int64_t discarded_samples = 0;
 
     while (!frame->buf[0]) {
-        ret = decode_simple_internal(avctx, frame);
+        if (discarded_samples > avctx->max_samples)
+            return AVERROR(EAGAIN);
+        ret = decode_simple_internal(avctx, frame, &discarded_samples);
         if (ret < 0)
             return ret;
     }