[FFmpeg-cvslog] avformat/iamf_parse: prevent overreads in update_extradata

[James Almer]

ffmpeg | branch: master | James Almer <jamrial at gmail.com> | Mon Jun 23 12:31:37 2025 -0300| [a7beac704b1c3ba38c487e2fa367bb7a84a6c382] | committer: James Almer

avformat/iamf_parse: prevent overreads in update_extradata

Fixes: libavcodec/put_bits.h:232:32: runtime error: shift exponent -19 is negative
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=a7beac704b1c3ba38c487e2fa367bb7a84a6c382
---

 libavformat/iamf_parse.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/libavformat/iamf_parse.c b/libavformat/iamf_parse.c
index 71497876ac..46a74ea679 100644
--- a/libavformat/iamf_parse.c
+++ b/libavformat/iamf_parse.c
@@ -288,7 +288,7 @@ static int update_extradata(AVCodecParameters *codecpar)
         uint8_t buf[6];
         int size = FFMIN(codecpar->extradata_size, sizeof(buf));
 
-        init_put_bits(&pb, buf, size);
+        init_put_bits(&pb, buf, sizeof(buf));
         ret = init_get_bits8(&gb, codecpar->extradata, size);
         if (ret < 0)
             return ret;
@@ -304,7 +304,10 @@ 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);
+        ret = get_bits_left(&gb);
+        if (ret < 0)
+            return AVERROR_INVALIDDATA;
+        ret = FFMIN(ret, put_bits_left(&pb));
         while (ret >= 32) {
            put_bits32(&pb, get_bits_long(&gb, 32));
            ret -= 32;
@@ -317,9 +320,10 @@ static int update_extradata(AVCodecParameters *codecpar)
     }
     case AV_CODEC_ID_FLAC: {
         uint8_t buf[13];
+        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);
+        ret = init_get_bits8(&gb, codecpar->extradata, size);
         if (ret < 0)
             return ret;
 
@@ -328,11 +332,14 @@ static int update_extradata(AVCodecParameters *codecpar)
         put_bits(&pb, 20, get_bits(&gb, 20)); // samplerate
         skip_bits(&gb, 3);
         put_bits(&pb, 3, codecpar->ch_layout.nb_channels - 1);
-        ret = put_bits_left(&pb);
+        ret = get_bits_left(&gb);
+        if (ret < 0)
+            return AVERROR_INVALIDDATA;
+        ret = FFMIN(ret, put_bits_left(&pb));
         put_bits(&pb, ret, get_bits(&gb, ret));
         flush_put_bits(&pb);
 
-        memcpy(codecpar->extradata, buf, sizeof(buf));
+        memcpy(codecpar->extradata, buf, put_bytes_output(&pb));
         break;
     }
     }