Re: [FFmpeg-devel] [PATCH v2] avcodec/dovi_rpu: verify RPU data CRC32

[James Almer <jamrial@gmail.com>]

On 8/9/2023 2:05 PM, quietvoid wrote:
> The Dolby Vision RPU contains a CRC32 to validate the payload against.
> The implementation is CRC32/MPEG-2.
> 
> The CRC is only verified with the AV_EF_CRCCHECK flag.
> 
> Signed-off-by: quietvoid <tcChlisop0@gmail.com>
> ---
>   libavcodec/dovi_rpu.c | 45 ++++++++++++++++++++++++++++++++++++++++---
>   libavcodec/dovi_rpu.h |  3 ++-
>   libavcodec/hevcdec.c  |  3 ++-
>   3 files changed, 46 insertions(+), 5 deletions(-)
> 
> diff --git a/libavcodec/dovi_rpu.c b/libavcodec/dovi_rpu.c
> index dd38936552..9ada0aceec 100644
> --- a/libavcodec/dovi_rpu.c
> +++ b/libavcodec/dovi_rpu.c
> @@ -22,6 +22,7 @@
>    */
>   
>   #include "libavutil/buffer.h"
> +#include "libavutil/crc.h"
>   
>   #include "dovi_rpu.h"
>   #include "golomb.h"
> @@ -191,13 +192,17 @@ static inline int64_t get_se_coef(GetBitContext *gb, const AVDOVIRpuDataHeader *
>           }                                                                       \
>       } while (0)
>   
> -int ff_dovi_rpu_parse(DOVIContext *s, const uint8_t *rpu, size_t rpu_size)
> +int ff_dovi_rpu_parse(DOVIContext *s, const uint8_t *rpu, size_t rpu_size,
> +                      int err_recognition)
>   {
>       AVDOVIRpuDataHeader *hdr = &s->header;
>       GetBitContext *gb = &(GetBitContext){0};
>       DOVIVdrRef *vdr;
>       int ret;
>   
> +    size_t actual_rpu_size;
> +    uint8_t trailing_zeroes = 0;
> +
>       uint8_t nal_prefix;
>       uint8_t rpu_type;
>       uint8_t vdr_seq_info_present;
> @@ -205,7 +210,22 @@ int ff_dovi_rpu_parse(DOVIContext *s, const uint8_t *rpu, size_t rpu_size)
>       uint8_t use_prev_vdr_rpu;
>       uint8_t use_nlq;
>       uint8_t profile;
> -    if ((ret = init_get_bits8(gb, rpu, rpu_size)) < 0)
> +
> +    uint32_t rpu_data_crc32;
> +    uint32_t computed_crc32;
> +
> +    for (int i = rpu_size - 1; i > 0; i--) {
> +        if (!rpu[i]) {
> +            trailing_zeroes++;
> +        } else {
> +            break;
> +        }
> +    }
> +
> +    actual_rpu_size = rpu_size - trailing_zeroes;
> +
> +    /* Exclude trailing byte (0x80) from reader */
> +    if ((ret = init_get_bits8(gb, rpu, actual_rpu_size - 1)) < 0)
>           return ret;
>   
>       /* RPU header, common values */
> @@ -440,7 +460,26 @@ int ff_dovi_rpu_parse(DOVIContext *s, const uint8_t *rpu, size_t rpu_size)
>           color->source_diagonal = get_bits(gb, 10);
>       }
>   
> -    /* FIXME: verify CRC32, requires implementation of AV_CRC_32_MPEG_2 */
> +    /* Skip unsupported until CRC32 */
> +    skip_bits_long(gb, get_bits_left(gb) - 32);

This can be done after the err_recognition check.

> +
> +    if (err_recognition & AV_EF_CRCCHECK) {

Do instead

if (!(err_recognition & AV_EF_CRCCHECK))
     return 0;

To remove one level of indentation.

> +        rpu_data_crc32 = get_bits_long(gb, 32);
> +
> +        /* Verify CRC32, buffer excludes the prefix, CRC32 and trailing byte */
> +        computed_crc32 = av_bswap32(av_crc(av_crc_get_table(AV_CRC_32_IEEE),
> +                                           -1, rpu + 1, actual_rpu_size - 6));
> +
> +        if (rpu_data_crc32 != computed_crc32) {
> +            av_log(s->logctx, AV_LOG_ERROR,
> +                   "RPU CRC mismatch! Expected %"PRIu32", received %"PRIu32"\n",
> +                   rpu_data_crc32, computed_crc32);
> +
> +            if (err_recognition & AV_EF_EXPLODE)
> +                goto fail;
> +        }
> +    }
> +
>       return 0;
>   
>   fail:
> diff --git a/libavcodec/dovi_rpu.h b/libavcodec/dovi_rpu.h
> index f6ca5bbbc5..2b993a72c6 100644
> --- a/libavcodec/dovi_rpu.h
> +++ b/libavcodec/dovi_rpu.h
> @@ -77,7 +77,8 @@ void ff_dovi_update_cfg(DOVIContext *s, const AVDOVIDecoderConfigurationRecord *
>    *
>    * Returns 0 or an error code.
>    */
> -int ff_dovi_rpu_parse(DOVIContext *s, const uint8_t *rpu, size_t rpu_size);
> +int ff_dovi_rpu_parse(DOVIContext *s, const uint8_t *rpu, size_t rpu_size,
> +                      int err_recognition);
>   
>   /**
>    * Attach the decoded AVDOVIMetadata as side data to an AVFrame.
> diff --git a/libavcodec/hevcdec.c b/libavcodec/hevcdec.c
> index df40c91ba6..81b1a84625 100644
> --- a/libavcodec/hevcdec.c
> +++ b/libavcodec/hevcdec.c
> @@ -3182,7 +3182,8 @@ static int decode_nal_units(HEVCContext *s, const uint8_t *buf, int length)
>               return AVERROR(ENOMEM);
>           memcpy(s->rpu_buf->data, nal->raw_data + 2, nal->raw_size - 2);
>   
> -        ret = ff_dovi_rpu_parse(&s->dovi_ctx, nal->data + 2, nal->size - 2);
> +        ret = ff_dovi_rpu_parse(&s->dovi_ctx, nal->data + 2, nal->size - 2,
> +                                s->avctx->err_recognition);
>           if (ret < 0) {
>               av_buffer_unref(&s->rpu_buf);
>               av_log(s->avctx, AV_LOG_WARNING, "Error parsing DOVI NAL unit.\n");
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