On Tue, 03. Dec 21:42, Andriy Gelman wrote:
> On Wed, 04. Dec 01:26, Andreas Rheinhardt wrote:
> > On Wed, Dec 4, 2019 at 1:04 AM Andriy Gelman <andriy.gel...@gmail.com>
> > wrote:
> >
> > > From: Andriy Gelman <andriy.gel...@gmail.com>
> > >
> > > Check packet grow size against INT_MAX instead of SIZE_MAX.
> > >
> > > Found with libFuzzer:
> > > 4294967044 cannot be represented as int.
> > >
> > > Signed-off-by: Andriy Gelman <andriy.gel...@gmail.com>
> > > ---
> > > libavcodec/hevc_mp4toannexb_bsf.c | 6 +++---
> > > 1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/libavcodec/hevc_mp4toannexb_bsf.c
> > > b/libavcodec/hevc_mp4toannexb_bsf.c
> > > index 09bce5b34c2..bf4c25b3b7b 100644
> > > --- a/libavcodec/hevc_mp4toannexb_bsf.c
> > > +++ b/libavcodec/hevc_mp4toannexb_bsf.c
> > > @@ -66,7 +66,7 @@ static int hevc_extradata_to_annexb(AVBSFContext *ctx)
> > > for (j = 0; j < cnt; j++) {
> > > int nalu_len = bytestream2_get_be16(&gb);
> > >
> > > - if (4 + AV_INPUT_BUFFER_PADDING_SIZE + nalu_len > SIZE_MAX -
> > > new_extradata_size) {
> > > + if (4 + AV_INPUT_BUFFER_PADDING_SIZE + nalu_len > INT_MAX -
> > > new_extradata_size) {
> > >
>
> >
> > There is actually FF_MAX_EXTRADATA_SIZE constant to limit the size of
> > extradata (it is chosen so small that one can parse the extradata via a
> > GetBitContext). (But honestly, it is not used consistently.)
>
> If we decide to use it should be a separate commit IMO.
>
> >
> >
> > > ret = AVERROR_INVALIDDATA;
> > > goto fail;
> > > }
> > > @@ -152,8 +152,8 @@ static int hevc_mp4toannexb_filter(AVBSFContext *ctx,
> > > AVPacket *out)
> > > extra_size = add_extradata * ctx->par_out->extradata_size;
> > > got_irap |= is_irap;
> > >
> > > - if (SIZE_MAX - nalu_size < 4 ||
> > > - SIZE_MAX - 4 - nalu_size < extra_size) {
> > > + if (INT_MAX < 4 + (uint64_t)nalu_size ||
> > >
> >
> > The cast is unnecessary: INT_MAX - 4 < nalu_size does the same. And INT_MAX
> > - 4 can even be computed at compile-time.
> >
> >
>
> > > + INT_MAX - 4 < extra_size + (uint64_t)nalu_size) {
> > >
> >
> > If you check that the extradata is not too big (namely <= INT_MAX - 4),
> > then you can simplify this to INT_MAX - 4 - extra_size < nalu_size. The
> > left side is positive, so it does not wrap around when converting it to
> > uint32_t. This makes the first check superfluous.
>
> Yes, that's a good idea. And I think that extra_size <= INT_MAX - 4 always
> holds
> because we pad extradata with AV_INPUT_PADDING_SIZE (and the checks are done
> in
> the initialization). But I'll double check.
The above check also needs to take into account the current packet size, i.e.:
INT_MAX - 4 - extra_size < (uint64_t)nalu_size + out->size
I don't think it's possible to get rid of the cast on the rhs then.
Thanks,
--
Andriy
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