[FFmpeg-devel] [PATCH] apedec: ensure blockstodecode is large enough

[Andreas Cadhalpun]

s->decoded_buffer is allocated with a min_size of:
    2 * FFALIGN(blockstodecode, 8) * sizeof(*s->decoded_buffer)

Then it is assigned to s->decoded[0], which is passed as out buffer to
decode_array_0000.

In this function 64 elements of the out buffer are written
unconditionally and outside the array if blocksdecode is too small.

This causes memory corruption, leading to segmentation faults or other crashes.

Thus check that FFALIGN(blockstodecode, 8) is at least 32, i. e. the
decoded_buffer has at least 64 components.

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
---
 libavcodec/apedec.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/libavcodec/apedec.c b/libavcodec/apedec.c
index 536361c..06f3d3f 100644
--- a/libavcodec/apedec.c
+++ b/libavcodec/apedec.c
@@ -1481,6 +1481,12 @@ static int ape_decode_frame(AVCodecContext *avctx, void *data,
     if (s->fileversion < 3930)
         blockstodecode = s->samples;
 
+    if (FFALIGN(blockstodecode, 8) < 32) {
+        av_log(avctx, AV_LOG_ERROR, "Too few blocks to decode %d (< 32)\n",
+               FFALIGN(blockstodecode, 8));
+        return AVERROR_INVALIDDATA;
+    }
+
     /* reallocate decoded sample buffer if needed */
     av_fast_malloc(&s->decoded_buffer, &s->decoded_size,
                    2 * FFALIGN(blockstodecode, 8) * sizeof(*s->decoded_buffer));
-- 
2.1.4