[FFmpeg-devel] [PATCH 1/3] avcodec/bitstream_template: Basic documentation for read_vlc_multi()

[FFmpeg-devel] [PATCH 1/3] avcodec/bitstream_template: Basic documentation for read_vlc_multi()

[Michael Niedermayer]

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/bitstream_template.h | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/libavcodec/bitstream_template.h b/libavcodec/bitstream_template.h
index cf4aeff4feb..4f3d07275fb 100644
--- a/libavcodec/bitstream_template.h
+++ b/libavcodec/bitstream_template.h
@@ -520,7 +520,20 @@ static inline int BS_FUNC(read_vlc)(BSCTX *bc, const VLCElem *table,
     return code;
 }
 
-static inline int BS_FUNC(read_vlc_multi)(BSCTX *bc, uint8_t *dst,
+/**
+ * Parse a vlc / vlc_multi code.
+ * @param bits is the number of bits which will be read at once, must be
+ *             identical to nb_bits in vlc_init()
+ * @param max_depth is the number of times bits bits must be read to completely
+ *                  read the longest vlc code
+ *                  = (max_vlc_length + bits - 1) / bits
+ * @param dst the parsed symbol(s) will be stored here. Up to 8 bytes are written
+ * @returns number of symbols parsed
+ * If the vlc code is invalid and max_depth=1, then no bits will be removed.
+ * If the vlc code is invalid and max_depth>1, then the number of bits removed
+ * is undefined.
+ */
+static inline int BS_FUNC(read_vlc_multi)(BSCTX *bc, uint8_t dst[8],
                                           const VLC_MULTI_ELEM *const Jtable,
                                           const VLCElem *const table,
                                           const int bits, const int max_depth)
-- 
2.17.1

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[FFmpeg-devel] [PATCH 2/3] avcodec/magicyuv: correct end of array check in multi VLC parsing

[Michael Niedermayer]

Fixes: out of array write
Fixes: 63390/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MAGICYUV_fuzzer-5144552979431424.fuzz

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

diff --git a/libavcodec/magicyuv.c b/libavcodec/magicyuv.c
index 3573db0f0ad..d813f209203 100644
--- a/libavcodec/magicyuv.c
+++ b/libavcodec/magicyuv.c
@@ -299,7 +299,7 @@ static int magy_decode_slice(AVCodecContext *avctx, void *tdata,
                 return ret;
 
             for (k = 0; k < height; k++)
-                READ_PLANE(dst, i, 1, 5)
+                READ_PLANE(dst, i, 1, 7)
         }
 
         switch (pred) {
-- 
2.17.1

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[FFmpeg-devel] [PATCH 3/3] avcodec/magicyuv: remove redundant check in inner loop

[Michael Niedermayer]

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/magicyuv.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/libavcodec/magicyuv.c b/libavcodec/magicyuv.c
index d813f209203..3f6348b531e 100644
--- a/libavcodec/magicyuv.c
+++ b/libavcodec/magicyuv.c
@@ -125,10 +125,9 @@ static void magicyuv_median_pred16(uint16_t *dst, const uint16_t *src1,
     for (; CACHED_BITSTREAM_READER && x < width-c && get_bits_left(&gb) > 0;) {\
         ret = get_vlc_multi(&gb, (uint8_t *)dst + x * b, multi, \
                             vlc, vlc_bits, 3); \
-        if (ret > 0) \
-            x += ret; \
         if (ret <= 0) \
             return AVERROR_INVALIDDATA; \
+        x += ret; \
     } \
     for (; x < width && get_bits_left(&gb) > 0; x++) \
         dst[x] = get_vlc2(&gb, vlc, vlc_bits, 3); \
-- 
2.17.1

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Re: [FFmpeg-devel] [PATCH 1/3] avcodec/bitstream_template: Basic documentation for read_vlc_multi()

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 554 bytes --]

On Sun, Oct 22, 2023 at 05:39:49PM +0200, Michael Niedermayer wrote:
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/bitstream_template.h | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)

will apply patchset, dont want to leave this open

[...]

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