[FFmpeg-devel] [PATCH] libavcodec/utils: Ensure allocated buffer is zero-initialized

[xjdeng <micro6947-at-gmail.com@ffmpeg.org>]

In `av_fast_padded_mallocz`, the allocated buffer's zero-initialization is not guaranteed.
This is because it calls `av_fast_malloc`, which in turn calls `fast_malloc` with `zero_realloc=0`.
Consequently, the memory returned by the underlying `av_malloc` (used within `fast_malloc`)
is not guaranteed to be zero-initialized.

Furthermore, if `*size` is adjusted to be greater than `min_size + AV_INPUT_BUFFER_PADDING_SIZE`,
the subsequent `memset` operation will not cover the entire allocated buffer,
leaving a portion of it uninitialized.

To ensure the entire allocated buffer is properly zero-initialized, we should use `FFMAX`
to adjust the `memset` range.

Signed-off-by: xjdeng <micro6947@gmail.com>

---
 libavcodec/utils.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/utils.c b/libavcodec/utils.c
index f2686b6863..e2afce71ef 100644
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -72,8 +72,8 @@ void av_fast_padded_mallocz(void *ptr, unsigned int *size, size_t min_size)
         return;
     }
     av_fast_malloc(p, size, min_size + AV_INPUT_BUFFER_PADDING_SIZE);
-    if (*p)
-        memset(*p, 0, min_size + AV_INPUT_BUFFER_PADDING_SIZE);
+    if (*p) 
+        memset(*p, 0, FFMAX(*size, min_size + AV_INPUT_BUFFER_PADDING_SIZE));
 }
 
 int av_codec_is_encoder(const AVCodec *avcodec)
-- 
2.27.0.windows.1

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