[FFmpeg-devel] [PATCH 2/2] avformat/id3v2: Check that decode_str() did advance

From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: [FFmpeg-devel] [PATCH 2/2] avformat/id3v2: Check that decode_str() did advance
Date: Sat, 12 Apr 2025 00:27:19 +0200
Message-ID: <20250411222719.2779176-2-michael@niedermayer.cc> (raw)
In-Reply-To: <20250411222719.2779176-1-michael@niedermayer.cc>

Fixes infinite loop with unknown encodings

We could alternatively error out from decode_str() or consume all of taglen
this would affect other callers though.

Fixes: 409819224/clusterfuzz-testcase-minimized-ffmpeg_dem_H261_fuzzer-6003527535362048
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavformat/id3v2.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libavformat/id3v2.c b/libavformat/id3v2.c
index 90314583a74..e3f7f9e2a90 100644
--- a/libavformat/id3v2.c
+++ b/libavformat/id3v2.c
@@ -341,10 +341,13 @@ static void read_ttag(AVFormatContext *s, AVIOContext *pb, int taglen,
     taglen--; /* account for encoding type byte */
 
     while (taglen > 1) {
+        int current_taglen = taglen;
         if (decode_str(s, pb, encoding, &dst, &taglen) < 0) {
             av_log(s, AV_LOG_ERROR, "Error reading frame %s, skipped\n", key);
             return;
         }
+        if (current_taglen == taglen)
+            return;
 
         count++;
 
-- 
2.49.0

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