tis 2019-11-26 klockan 20:29 +0100 skrev Paul B Mahol:
> On 11/26/19, James Almer <jamr...@gmail.com> wrote:
> > On 11/26/2019 6:47 AM, Paul B Mahol wrote:
> > > On 11/25/19, Tomas Härdin <tjop...@acc.umu.se> wrote:
> > > > mån 2019-11-25 klockan 22:09 +0100 skrev Paul B Mahol:
> > > > > Signed-off-by: Paul B Mahol <one...@gmail.com>
> > > > > +static int decode_mvdv(MidiVidContext *s, AVCodecContext *avctx,
> > > > > AVFrame
> > > > > *frame)
> > > > > +{
> > > > > + GetByteContext *gb = &s->gb;
> > > > > + GetBitContext mask;
> > > > > + GetByteContext idx9;
> > > > > + uint16_t nb_vectors, intra_flag;
> > > > > + const uint8_t *vec;
> > > > > + const uint8_t *mask_start;
> > > > > + uint8_t *skip;
> > > > > + int mask_size;
> > > > > + int idx9bits = 0;
> > > > > + int idx9val = 0;
> > > > > + int num_blocks;
> > > > > +
> > > > > + nb_vectors = bytestream2_get_le16(gb);
> > > > > + intra_flag = bytestream2_get_le16(gb);
> > > > > + if (intra_flag) {
> > > > > + num_blocks = (avctx->width / 2) * (avctx->height / 2);
> > > >
> > > > Will UB if width*height/4 > INT_MAX
> > > >
> > > > > + } else {
> > > > > + int skip_linesize;
> > > > > +
> > > > > + num_blocks = bytestream2_get_le32(gb);
> > > >
> > > > Might want to use uint32_t so this doesn't lead to weirdness on 32-bit
> > > >
> > > > > + skip_linesize = avctx->width >> 1;
> > > > > + mask_start = gb->buffer_start + bytestream2_tell(gb);
> > > > > + mask_size = (avctx->width >> 5) * (avctx->height >> 2);
> > > >
> > > > This can also UB
> > > >
> > > > /Tomas
> > > >
> > >
> > > Nothing of this can actually happen.
This assumes max_pixels will never be increased above INT_MAX. "64k"
video is most definitely within the range of possibility in the coming
years, if it isn't already. Film archival and DPX come to mind.
> > It can and i'm fairly sure it will happen as soon as the fuzzer starts
> > testing this decoder using big dimensions.
>
> I'm not that guy doing such work. Please stop bikesheding those
> patches for once.
This reads like an admission of pushing insecure code via "not my
problem"
> > You don't need asserts here, you just need to check the calculations
> > will not overflow. Do something like "if ((int64_t)avctx->width *
> > avctx->height / 4 > INT_MAX) return AVERROR_INVALIDDATA" and call it a day.
> > Also, maybe num_blocks should be unsigned, seeing you set it using
> > bytestream2_get_le32() for P-frames.
>
> No decoder does this.
zmbv does
All this is really about the lack of any way to reason about
assumptions like "dimensions can't be larger than X*Y" at compile time,
which is a thing I've been pointing out on this list for a while now.
/Tomas
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