[FFmpeg-devel] [PATCH 1/2] avcodec/bitstream: Check code length before truncating to uint8_t

[Andreas Rheinhardt]

Andreas Rheinhardt:
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
> The main motivation for this patch is actually the second patch and not
> the improved check.
> 
>  libavcodec/bitstream.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/libavcodec/bitstream.c b/libavcodec/bitstream.c
> index 77c2b9ce05..ffa352b28b 100644
> --- a/libavcodec/bitstream.c
> +++ b/libavcodec/bitstream.c
> @@ -302,15 +302,17 @@ int ff_init_vlc_sparse(VLC *vlc_arg, int nb_bits, int nb_codes,
>      j = 0;
>  #define COPY(condition)\
>      for (i = 0; i < nb_codes; i++) {                                        \
> -        GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size);               \
> +        unsigned len;                                                       \
> +        GET_DATA(len, bits, i, bits_wrap, bits_size);                       \
>          if (!(condition))                                                   \
>              continue;                                                       \
> -        if (buf[j].bits > 3*nb_bits || buf[j].bits>32) {                    \
> -            av_log(NULL, AV_LOG_ERROR, "Too long VLC (%d) in init_vlc\n", buf[j].bits);\
> +        if (len > 3*nb_bits || len > 32) {                                  \
> +            av_log(NULL, AV_LOG_ERROR, "Too long VLC (%u) in init_vlc\n", len);\
>              if (buf != localbuf)                                            \
>                  av_free(buf);                                               \
>              return AVERROR(EINVAL);                                         \
>          }                                                                   \
> +        buf[j].bits = len;                                                  \
>          GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);            \
>          if (buf[j].code >= (1LL<<buf[j].bits)) {                            \
>              av_log(NULL, AV_LOG_ERROR, "Invalid code %"PRIx32" for %d in "  \
> @@ -329,10 +331,10 @@ int ff_init_vlc_sparse(VLC *vlc_arg, int nb_bits, int nb_codes,
>              buf[j].symbol = i;                                              \
>          j++;                                                                \
>      }
> -    COPY(buf[j].bits > nb_bits);
> +    COPY(len > nb_bits);
>      // qsort is the slowest part of init_vlc, and could probably be improved or avoided
>      AV_QSORT(buf, j, struct VLCcode, compare_vlcspec);
> -    COPY(buf[j].bits && buf[j].bits <= nb_bits);
> +    COPY(len && len <= nb_bits);
>      nb_codes = j;
>  
>      ret = build_table(vlc, nb_bits, nb_codes, buf, flags);
> 
Will apply this later today unless there are objections.

- Andreas