[FFmpeg-cvslog] avcodec/ac3_parser: use a padded buffer in av_ac3_parse_header()

[James Almer]

ffmpeg | branch: master | James Almer <jamrial at gmail.com> | Thu Jun  5 21:07:14 2025 -0300| [efbcd312060a9598e7e63f0e8ca8515d8ce109ef] | committer: James Almer

avcodec/ac3_parser: use a padded buffer in av_ac3_parse_header()

The GetBitContext API requires the buffer to be padded, and the documentation for
av_ac3_parse_header() does not specify it, so use a temporary local buffer.

Signed-off-by: James Almer <jamrial at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=efbcd312060a9598e7e63f0e8ca8515d8ce109ef
---

 libavcodec/ac3_parser.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavcodec/ac3_parser.c b/libavcodec/ac3_parser.c
index 69989690dd..1d9a40a8d9 100644
--- a/libavcodec/ac3_parser.c
+++ b/libavcodec/ac3_parser.c
@@ -202,9 +202,13 @@ int av_ac3_parse_header(const uint8_t *buf, size_t size,
 {
     GetBitContext gb;
     AC3HeaderInfo hdr;
+    uint8_t tmp[32 + AV_INPUT_BUFFER_PADDING_SIZE];
     int err;
 
-    err = init_get_bits8(&gb, buf, size);
+    size = FFMIN(32, size);
+    memcpy(tmp, buf, size);
+    memset(tmp + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
+    err = init_get_bits8(&gb, tmp, size);
     if (err < 0)
         return AVERROR_INVALIDDATA;
     err = ff_ac3_parse_header(&gb, &hdr);