Re: [FFmpeg-devel] [PATCH v1 2/3] avcodec/jpeg2000dec: add support for HTJ2K block decoding

[Michael Niedermayer <michael@niedermayer.cc>]

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On Sun, Apr 02, 2023 at 03:21:08PM -0700, Pierre-Anthony Lemieux wrote:
> On Sun, Apr 2, 2023 at 3:17 PM Michael Niedermayer
> <michael@niedermayer.cc> wrote:
> >
> > On Fri, Mar 31, 2023 at 08:29:40AM -0700, pal@sandflow.com wrote:
> > > From: caleb <etemesicaleb@gmail.com>
[...]
> > [...]
> > > +/**
> > > + * Drops bits from lower bits in the bit buffer. buf contains the bit buffers.
> > > + * nbits is the number of bits to remove.
> > > + */
> > > +av_always_inline
> > > +static void jpeg2000_bitbuf_drop_bits_lsb(StateVars *buf, uint8_t nbits)
> > > +{
> > > +    if (buf->bits_left < nbits) {
> >
> > > +        av_log(NULL, AV_LOG_ERROR, "Invalid bit read of %d, bits in buffer are %d\n", nbits, buf->bits_left);
> > > +        av_assert0(0);
> >
> >
> > [...]
> > > +int
> > > +ff_jpeg2000_decode_htj2k(const Jpeg2000DecoderContext *s, Jpeg2000CodingStyle *codsty, Jpeg2000T1Context *t1, Jpeg2000Cblk *cblk,
> > > +                         int width, int height, int magp, uint8_t roi_shift)
> > > +{
> > > +    uint8_t p0 = 0;             // Number of placeholder passes
> > > +    uint32_t Lcup;              // Length of HT cleanup segment
> > > +    uint32_t Lref;              // Length of Refinement segment
> > > +    uint32_t Scup;              // HT cleanup segment suffix length
> > > +    uint32_t Pcup;              // HT cleanup segment prefix length
> > > +
> > > +    uint8_t S_blk;              // Number of skipped magnitude bitplanes
> > > +    uint8_t pLSB;
> > > +
> > > +    uint8_t *Dcup;              // Byte of an HT cleanup segment
> > > +    uint8_t *Dref;              // Byte of an HT refinement segment
> > > +
> > > +    int z_blk;                  // Number of ht coding pass
> > > +
> > > +    uint8_t empty_passes;
> > > +
> > > +    StateVars mag_sgn;          // Magnitude and Sign
> > > +    StateVars mel;              // Adaptive run-length coding
> > > +    StateVars vlc;              // Variable Length coding
> > > +    StateVars sig_prop;         // Significance propagation
> > > +
> > > +    MelDecoderState mel_state;
> > > +
> > > +    int ret;
> > > +
> > > +    /* Temporary buffers */
> > > +    int32_t *sample_buf;
> > > +    uint8_t *block_states;
> > > +
> > > +    int32_t n, val;             // Post-processing
> > > +
> > > +    int32_t M_b = magp;
> > > +    av_assert0(width <= 1024U && height <= 1024U);
> > > +    av_assert0(width * height <= 4096);
> > > +    av_assert0(width * height > 0);
> >
> > Has this decoder been tested with some fuzzer ?
> 
> Yes.

ok


> 
> > I see a bunch of asserts in it and i dont immedeatly see what would prevent them from
> > triggering

maybe you can add comments to the asserts that explain why these are
guranteed to be true

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Modern terrorism, a quick summary: Need oil, start war with country that
has oil, kill hundread thousand in war. Let country fall into chaos,
be surprised about raise of fundamantalists. Drop more bombs, kill more
people, be surprised about them taking revenge and drop even more bombs
and strip your own citizens of their rights and freedoms. to be continued

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