n Thu, 26 Jun 2025 at 16:07, Zhao Zhili <quinkblack-at-foxmail....@ffmpeg.org> wrote: > > > > > On Jun 26, 2025, at 12:07, xjdeng <micro6947-at-gmail....@ffmpeg.org> wrote: > > > > 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. > > I think memset size is enough. size >= min_size + > AV_INPUT_BUFFER_PADDING_SIZE. > > > > > Signed-off-by: xjdeng <micro6...@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)); > > }
I think the current code is intentional. In av_fast_malloc() and siblings the `*size` is the real allocation size, but your working area that you should be using is ` min_size` and hence why this area (+padding) is zeroed. You shouldn't be using anything beyond that, as it is allocated space, but "not active" right now. These functions are meant to be `fast` by not reallocating when there is enough space for user payload, and part of the `fast` part is also not zeroing the memory area that you as a user don't request in `min_size` parameter. - Kacper _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
