[FFmpeg-devel] [PATCH 2/6] avcodec/pngdec: Check deloco index more exactly

From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: [FFmpeg-devel] [PATCH 2/6] avcodec/pngdec: Check deloco index more exactly
Date: Thu, 12 Jan 2023 00:54:28 +0100
Message-ID: <20230111235432.2135-2-michael@niedermayer.cc> (raw)
In-Reply-To: <20230111235432.2135-1-michael@niedermayer.cc>

Fixes: out of array access:
Fixes: 48567/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PNG_fuzzer-6716193709096960

Alternatively it should be possible to limit this to 3 plane RGB 8 /16bit to ensure the size is what it should be

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

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index f1cad26c52..cb4162d2ab 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -322,7 +322,7 @@ void ff_png_filter_row(PNGDSPContext *dsp, uint8_t *dst, int filter_type,
 static void deloco_ ## NAME(TYPE *dst, int size, int alpha) \
 { \
     int i; \
-    for (i = 0; i < size; i += 3 + alpha) { \
+    for (i = 0; i < size - 2; i += 3 + alpha) { \
         int g = dst [i + 1]; \
         dst[i + 0] += g; \
         dst[i + 2] += g; \
-- 
2.17.1

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