[FFmpeg-devel] [PATCH 1/2] avformat/rtmppkt: Convert ff_amf_tag_size() to bytestream2

[James Almer]

On 7/28/2017 10:47 AM, Michael Niedermayer wrote:
> Fixes: out of array accesses
> Fixes: crash-9238fa9e8d4fde3beda1f279626f53812cb001cb-SEGV
> 
> Found-by: JunDong Xie of Ant-financial Light-Year Security Lab
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavformat/rtmppkt.c | 60 ++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 40 insertions(+), 20 deletions(-)
> 
> diff --git a/libavformat/rtmppkt.c b/libavformat/rtmppkt.c
> index 833a3dbade..752d92a42b 100644
> --- a/libavformat/rtmppkt.c
> +++ b/libavformat/rtmppkt.c
> @@ -433,50 +433,70 @@ void ff_rtmp_packet_destroy(RTMPPacket *pkt)
>      pkt->size = 0;
>  }
>  
> -int ff_amf_tag_size(const uint8_t *data, const uint8_t *data_end)
> +static int ff_amf_tag_skip(GetByteContext *gb)

It's static, so no ff_ prefix.

>  {
> -    const uint8_t *base = data;
>      AMFDataType type;
>      unsigned nb   = -1;
>      int parse_key = 1;
>  
> -    if (data >= data_end)
> +    if (bytestream2_get_bytes_left(gb) < 1)
>          return -1;
> -    switch ((type = *data++)) {
> -    case AMF_DATA_TYPE_NUMBER:      return 9;
> -    case AMF_DATA_TYPE_BOOL:        return 2;
> -    case AMF_DATA_TYPE_STRING:      return 3 + AV_RB16(data);
> -    case AMF_DATA_TYPE_LONG_STRING: return 5 + AV_RB32(data);
> -    case AMF_DATA_TYPE_NULL:        return 1;
> -    case AMF_DATA_TYPE_DATE:        return 11;
> +
> +    switch ((type = bytestream2_get_byte(gb))) {

type = bytestream2_get_byte(gb);
switch(type) {

> +    case AMF_DATA_TYPE_NUMBER:      bytestream2_get_be64(gb); return 0;
> +    case AMF_DATA_TYPE_BOOL:        bytestream2_get_byte(gb); return 0;
> +    case AMF_DATA_TYPE_STRING:
> +        bytestream2_skip(gb, bytestream2_get_be16(gb));
> +        return 0;
> +    case AMF_DATA_TYPE_LONG_STRING:
> +        bytestream2_skip(gb, bytestream2_get_be32(gb));
> +        return 0;
> +    case AMF_DATA_TYPE_NULL:        return 0;
> +    case AMF_DATA_TYPE_DATE:        bytestream2_skip(gb, 10); return 0;

Use separate lines for all the above or reorder them, for readability's
sake.

>      case AMF_DATA_TYPE_ARRAY:
>          parse_key = 0;
>      case AMF_DATA_TYPE_MIXEDARRAY:
> -        nb = bytestream_get_be32(&data);
> +        nb = bytestream2_get_be32(gb);
>      case AMF_DATA_TYPE_OBJECT:
>          while (nb-- > 0 || type != AMF_DATA_TYPE_ARRAY) {
>              int t;
>              if (parse_key) {
> -                int size = bytestream_get_be16(&data);
> +                int size = bytestream2_get_be16(gb);
>                  if (!size) {
> -                    data++;
> +                    bytestream2_get_byte(gb);
>                      break;
>                  }
> -                if (size < 0 || size >= data_end - data)
> +                if (size < 0 || size >= bytestream2_get_bytes_left(gb))
>                      return -1;
> -                data += size;
> +                bytestream2_skip(gb, size);
>              }
> -            t = ff_amf_tag_size(data, data_end);
> -            if (t < 0 || t >= data_end - data)
> +            t = ff_amf_tag_skip(gb);
> +            if (t < 0 || bytestream2_get_bytes_left(gb) <= 0)
>                  return -1;
> -            data += t;
>          }
> -        return data - base;
> -    case AMF_DATA_TYPE_OBJECT_END:  return 1;
> +        return 0;
> +    case AMF_DATA_TYPE_OBJECT_END:  return 0;
>      default:                        return -1;
>      }
>  }
>  
> +int ff_amf_tag_size(const uint8_t *data, const uint8_t *data_end)
> +{
> +    GetByteContext gb;
> +    int ret;
> +
> +    if (data >= data_end)
> +        return -1;
> +
> +    bytestream2_init(&gb, data, data_end - data);
> +
> +    ret = ff_amf_tag_skip(&gb);
> +    if (ret < 0 || bytestream2_get_bytes_left(&gb) <= 0)
> +        return -1;
> +    av_assert0(bytestream2_tell(&gb) >= 0 && bytestream2_tell(&gb) <= data_end - data);
> +    return bytestream2_tell(&gb);
> +}
> +
>  int ff_amf_get_field_value(const uint8_t *data, const uint8_t *data_end,
>                             const uint8_t *name, uint8_t *dst, int dst_size)
>  {
>