On 4/16/2023 1:48 PM, Michael Niedermayer wrote:
Fixes: signed integer overflow: 3011809745540902265 + 6323452730883571725 
cannot be represented in type 'long'
Fixes: 
45982/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FLAC_fuzzer-6687553022722048

Found-by: continuous fuzzing process 
https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc>
---
  libavcodec/flacdec.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/flacdec.c b/libavcodec/flacdec.c
index cc778a8dff1..524a0469495 100644
--- a/libavcodec/flacdec.c
+++ b/libavcodec/flacdec.c
@@ -513,7 +513,7 @@ static int decode_subframe_lpc_33bps(FLACContext *s, 
int64_t *decoded,
      for (i = pred_order; i < s->blocksize; i++, decoded++) {
          int64_t sum = 0;
          for (j = 0; j < pred_order; j++)
-            sum += (int64_t)coeffs[j] * decoded[j];
+            sum += (int64_t)coeffs[j] * (uint64_t)decoded[j];

Why not instead do

sum = av_sat_add64(sum, (int64_t)coeffs[j] * decoded[j]);

Also, decoded[j] is an int64_t, so wouldn't coeffs[j] be promoted if you swap the order in the multiplication, thus saving the cast?

          decoded[j] = residual[i] + (sum >> qlevel);
      }
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