[FFmpeg-cvslog] avformat/iamf_parse: increase PutBytes buffer when writing AAC extradata

[James Almer]

ffmpeg | branch: master | James Almer <jamrial at gmail.com> | Sat May 10 12:50:37 2025 -0300| [3f9420132441345b7ccd57001f230bb98f655696] | committer: James Almer

avformat/iamf_parse: increase PutBytes buffer when writing AAC extradata

We may write up to 43 bits, so 5 bytes is not enough.

Fixes: Assertion n>=0 && n<=32 failed at ./libavcodec/get_bits.h:406
Fixes: 398527871/clusterfuzz-testcase-minimized-ffmpeg_dem_IAMF_fuzzer-6602025714647040

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: James Almer <jamrial at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=3f9420132441345b7ccd57001f230bb98f655696
---

 libavformat/iamf_parse.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/libavformat/iamf_parse.c b/libavformat/iamf_parse.c
index abedfdb066..71497876ac 100644
--- a/libavformat/iamf_parse.c
+++ b/libavformat/iamf_parse.c
@@ -285,10 +285,11 @@ static int update_extradata(AVCodecParameters *codecpar)
         AV_WL16A(codecpar->extradata + 16, AV_RB16A(codecpar->extradata + 16)); // Byte swap Output Gain
         break;
     case AV_CODEC_ID_AAC: {
-        uint8_t buf[5];
+        uint8_t buf[6];
+        int size = FFMIN(codecpar->extradata_size, sizeof(buf));
 
-        init_put_bits(&pb, buf, sizeof(buf));
-        ret = init_get_bits8(&gb, codecpar->extradata, codecpar->extradata_size);
+        init_put_bits(&pb, buf, size);
+        ret = init_get_bits8(&gb, codecpar->extradata, size);
         if (ret < 0)
             return ret;
 
@@ -304,6 +305,10 @@ static int update_extradata(AVCodecParameters *codecpar)
         skip_bits(&gb, 4);
         put_bits(&pb, 4, codecpar->ch_layout.nb_channels); // set channel config
         ret = put_bits_left(&pb);
+        while (ret >= 32) {
+           put_bits32(&pb, get_bits_long(&gb, 32));
+           ret -= 32;
+        }
         put_bits(&pb, ret, get_bits_long(&gb, ret));
         flush_put_bits(&pb);