Re: [FFmpeg-devel] [PATCH 3/3] avcodec/jpeg2000htdec: Check m

[Pierre-Anthony Lemieux <pal@sandflow.com>]

On Tue, Aug 1, 2023 at 5:02 PM Michael Niedermayer
<michael@niedermayer.cc> wrote:
>
> This also fixes assertion failures
>
> Fixes: shift exponent 95 is too large for 64-bit type 'unsigned long long'
> Fixes: 58299/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5828618092937216
>
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/jpeg2000htdec.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/jpeg2000htdec.c b/libavcodec/jpeg2000htdec.c
> index 3985783f3a..ae2ee6d6ee 100644
> --- a/libavcodec/jpeg2000htdec.c
> +++ b/libavcodec/jpeg2000htdec.c
> @@ -689,6 +689,10 @@ static int jpeg2000_decode_ht_cleanup_segment(const Jpeg2000DecoderContext *s,
>          for (int i = 0; i < 4; i++) {
>              m[J2K_Q1][i] = sigma_n[4 * q1 + i] * U[J2K_Q1] - ((emb_pat_k[J2K_Q1] >> i) & 1);
>              m[J2K_Q2][i] = sigma_n[4 * q2 + i] * U[J2K_Q2] - ((emb_pat_k[J2K_Q2] >> i) & 1);
> +            if (m[J2K_Q1][i] > 63 || m[J2K_Q2][i] > 63) {

AFAIK, m[i], which is m_n in the standard, can never be larger than
the sample bit depth (including the sign bit, if any). Is it worth
comparing it to a value more precise than 63?

> +                ret = AVERROR_INVALIDDATA;
> +                goto free;
> +            }
>          }
>
>          recover_mag_sgn(mag_sgn_stream, J2K_Q1, q1, m_n, known_1, emb_pat_1, v, m,
> @@ -723,8 +727,13 @@ static int jpeg2000_decode_ht_cleanup_segment(const Jpeg2000DecoderContext *s,
>
>          U[J2K_Q1] = kappa[J2K_Q1] + u[J2K_Q1];
>
> -        for (int i = 0; i < 4; i++)
> +        for (int i = 0; i < 4; i++) {
>              m[J2K_Q1][i] = sigma_n[4 * q1 + i] * U[J2K_Q1] - ((emb_pat_k[J2K_Q1] >> i) & 1);
> +            if (m[J2K_Q1][i] > 63) {
> +                ret = AVERROR_INVALIDDATA;
> +                goto free;
> +            }
> +        }
>
>          recover_mag_sgn(mag_sgn_stream, J2K_Q1, q1, m_n, known_1, emb_pat_1, v, m,
>                          E, mu_n, Dcup, Pcup, pLSB);
> @@ -855,6 +864,10 @@ static int jpeg2000_decode_ht_cleanup_segment(const Jpeg2000DecoderContext *s,
>              for (int i = 0; i < 4; i++) {
>                  m[J2K_Q1][i] = sigma_n[4 * q1 + i] * U[J2K_Q1] - ((emb_pat_k[J2K_Q1] >> i) & 1);
>                  m[J2K_Q2][i] = sigma_n[4 * q2 + i] * U[J2K_Q2] - ((emb_pat_k[J2K_Q2] >> i) & 1);
> +                if (m[J2K_Q1][i] > 63 || m[J2K_Q2][i] > 63) {
> +                    ret = AVERROR_INVALIDDATA;
> +                    goto free;
> +                }
>              }
>              recover_mag_sgn(mag_sgn_stream, J2K_Q1, q1, m_n, known_1, emb_pat_1, v, m,
>                              E, mu_n, Dcup, Pcup, pLSB);
> @@ -920,8 +933,13 @@ static int jpeg2000_decode_ht_cleanup_segment(const Jpeg2000DecoderContext *s,
>
>              U[J2K_Q1] = kappa[J2K_Q1] + u[J2K_Q1];
>
> -            for (int i = 0; i < 4; i++)
> +            for (int i = 0; i < 4; i++) {
>                  m[J2K_Q1][i] = sigma_n[4 * q1 + i] * U[J2K_Q1] - ((emb_pat_k[J2K_Q1] >> i) & 1);
> +                if (m[J2K_Q1][i] > 63) {
> +                    ret = AVERROR_INVALIDDATA;
> +                    goto free;
> +                }
> +            }
>
>              recover_mag_sgn(mag_sgn_stream, J2K_Q1, q1, m_n, known_1, emb_pat_1, v, m,
>                              E, mu_n, Dcup, Pcup, pLSB);
> --
> 2.17.1
>
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