Re: [FFmpeg-devel] [PATCH 1/1] fix: use declared size for attribute of type string to ensure full value used and prevent parse failure for string lengths longer than 256

[Paul B Mahol <onemda@gmail.com>]

On Thu, May 12, 2022 at 5:31 PM vectronic <hello.vectronic@gmail.com> wrote:

> Signed-off-by: vectronic <hello.vectronic@gmail.com>
> ---
>  libavcodec/exr.c | 32 +++++++++++++++++++++++---------
>  1 file changed, 23 insertions(+), 9 deletions(-)
>
> diff --git a/libavcodec/exr.c b/libavcodec/exr.c
> index 8cd867a32f..bc2afcee53 100644
> --- a/libavcodec/exr.c
> +++ b/libavcodec/exr.c
> @@ -1912,10 +1912,13 @@ static int decode_header(EXRContext *s, AVFrame
> *frame)
>              continue;
>          } else if ((var_size = check_header_variable(s, "writer",
>                                                       "string", 1)) >= 0) {
> -            uint8_t key[256] = { 0 };
> +            uint8_t *key = av_malloc(var_size);
>
> -            bytestream2_get_buffer(gb, key, FFMIN(sizeof(key) - 1,
> var_size));
> -            av_dict_set(&metadata, "writer", key, 0);
> +            if (!key)
> +                return AVERROR(ENOMEM);
> +
> +            bytestream2_get_buffer(gb, key, var_size);
> +            av_dict_set(&metadata, "writer", key,
> AV_DICT_DONT_STRDUP_VAL);
>

var_size can be very big number, potentially causing attacks vectors.


>
>              continue;
>          } else if ((var_size = check_header_variable(s, "framesPerSecond",
> @@ -1937,9 +1940,12 @@ static int decode_header(EXRContext *s, AVFrame
> *frame)
>              continue;
>          } else if ((var_size = check_header_variable(s, "type",
>                                                       "string", 16)) >= 0)
> {
> -            uint8_t key[256] = { 0 };
> +            uint8_t *key = av_malloc(var_size);
> +
> +            if (!key)
> +                return AVERROR(ENOMEM);
>
> -            bytestream2_get_buffer(gb, key, FFMIN(sizeof(key) - 1,
> var_size));
> +            bytestream2_get_buffer(gb, key, var_size);
>              if (strncmp("scanlineimage", key, var_size) &&
>                  strncmp("tiledimage", key, var_size))
>                  return AVERROR_PATCHWELCOME;
> @@ -1970,7 +1976,6 @@ static int decode_header(EXRContext *s, AVFrame
> *frame)
>          {
>              uint8_t name[256] = { 0 };
>              uint8_t type[256] = { 0 };
> -            uint8_t value[256] = { 0 };
>              int i = 0, size;
>
>              while (bytestream2_get_bytes_left(gb) > 0 &&
> @@ -1987,9 +1992,18 @@ static int decode_header(EXRContext *s, AVFrame
> *frame)
>              bytestream2_skip(gb, 1);
>              size = bytestream2_get_le32(gb);
>
> -            bytestream2_get_buffer(gb, value, FFMIN(sizeof(value) - 1,
> size));
> -            if (!strcmp(type, "string"))
> -                av_dict_set(&metadata, name, value, 0);
> +            if (strcmp(type, "string") != 0) {
> +                bytestream2_skip(gb, size);
> +
> +                continue;
> +            }
> +            uint8_t *value = av_malloc(size);
> +
> +            if (!value)
> +                return AVERROR(ENOMEM);
> +
> +            bytestream2_get_buffer(gb, value, size);
> +            av_dict_set(&metadata, name, value, AV_DICT_DONT_STRDUP_VAL);
>          }
>      }
>
> --
> 2.32.0 (Apple Git-132)
>
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