Thank you very much — I think you've convinced me. This was my first time asking a question in the FFmpeg community, and my limited understanding of the code led to a false positive. I apologize for the delayed response, and I truly appreciate your time and help.
Kacper Michajlow <kaspe...@gmail.com> 于2025年6月27日周五 02:16写道： > 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".
