[FFmpeg-cvslog] avcodec/alsdec: Avoid dereferencing context pointer in inner interleave loop

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Wed Sep 25 20:31:50 2019 +0200| [581a895c5c8b464a7fc7ebbaa6d9f565c10bae62] | committer: Michael Niedermayer

avcodec/alsdec: Avoid dereferencing context pointer in inner interleave loop

This makes the decoder faster

Improves/Fixes: Timeout (22sec -> 20sec)
Testcase: 17619/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5078510820917248

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Paul B Mahol <onemda at gmail.com>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=581a895c5c8b464a7fc7ebbaa6d9f565c10bae62
---

 libavcodec/alsdec.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/libavcodec/alsdec.c b/libavcodec/alsdec.c
index a53c170d18..56313d206c 100644
--- a/libavcodec/alsdec.c
+++ b/libavcodec/alsdec.c
@@ -1815,15 +1815,17 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame_ptr,
     #define INTERLEAVE_OUTPUT(bps)                                                   \
     {                                                                                \
         int##bps##_t *dest = (int##bps##_t*)frame->data[0];                          \
+        int channels = avctx->channels;                                              \
+        int32_t **raw_samples = ctx->raw_samples;                                    \
         shift = bps - ctx->avctx->bits_per_raw_sample;                               \
         if (!ctx->cs_switch) {                                                       \
             for (sample = 0; sample < ctx->cur_frame_length; sample++)               \
-                for (c = 0; c < avctx->channels; c++)                                \
-                    *dest++ = ctx->raw_samples[c][sample] * (1U << shift);            \
+                for (c = 0; c < channels; c++)                                       \
+                    *dest++ = raw_samples[c][sample] * (1U << shift);                \
         } else {                                                                     \
             for (sample = 0; sample < ctx->cur_frame_length; sample++)               \
-                for (c = 0; c < avctx->channels; c++)                                \
-                    *dest++ = ctx->raw_samples[sconf->chan_pos[c]][sample] * (1U << shift); \
+                for (c = 0; c < channels; c++)                                       \
+                    *dest++ = raw_samples[sconf->chan_pos[c]][sample] * (1U << shift);\
         }                                                                            \
     }