Re: [FFmpeg-devel] [PATCH] [RFC] avformat: Add basic same origin check

[James Almer <jamrial@gmail.com>]

On 5/2/2023 4:36 PM, Michael Niedermayer wrote:
> TODO: bump minor version, add docs
> 
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>   libavformat/avformat.h      | 10 ++++++++++
>   libavformat/options.c       | 29 +++++++++++++++++++++++++++++
>   libavformat/options_table.h |  3 +++
>   3 files changed, 42 insertions(+)
> 
> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> index 1916aa2dc5..5ff77323ba 100644
> --- a/libavformat/avformat.h
> +++ b/libavformat/avformat.h
> @@ -1713,6 +1713,16 @@ typedef struct AVFormatContext {
>        * @return 0 on success, a negative AVERROR code on failure
>        */
>       int (*io_close2)(struct AVFormatContext *s, AVIOContext *pb);
> +
> +    /**
> +     * Perform basic same origin checks in default io_open()
> +     * - encoding: set by user
> +     * - decoding: set by user
> +     */
> +    int same_origin_check;
> +#define AVFMT_SAME_ORIGIN_CHECK_NONE 0  //no check
> +#define AVFMT_SAME_ORIGIN_CHECK_HOST 1  //protocol, host, auth, port
> +#define AVFMT_SAME_ORIGIN_CHECK_PATH 2  //protocol, host, auth, port, parent path
>   } AVFormatContext;
>   
>   /**
> diff --git a/libavformat/options.c b/libavformat/options.c
> index e4a3aceed0..7db4bc9b38 100644
> --- a/libavformat/options.c
> +++ b/libavformat/options.c
> @@ -26,6 +26,7 @@
>   #include "libavcodec/codec_par.h"
>   
>   #include "libavutil/avassert.h"
> +#include "libavutil/avstring.h"
>   #include "libavutil/internal.h"
>   #include "libavutil/intmath.h"
>   #include "libavutil/opt.h"
> @@ -148,6 +149,34 @@ static int io_open_default(AVFormatContext *s, AVIOContext **pb,
>   
>       av_log(s, loglevel, "Opening \'%s\' for %s\n", url, flags & AVIO_FLAG_WRITE ? "writing" : "reading");
>   
> +    if (s->same_origin_check) {
> +        URLComponents uc;
> +        int err;
> +        size_t len;
> +        const char *end;
> +        err = ff_url_decompose(&uc, s->url, NULL);
> +        if (err < 0)
> +            return err;
> +
> +        if (s->same_origin_check == AVFMT_SAME_ORIGIN_CHECK_PATH) {
> +            end = uc.query;
> +            while (end > uc.path && *end != '/')
> +                end--;
> +        } else
> +            end = uc.path;
> +
> +        len = end - s->url;
> +        if (strncmp(url, s->url, len)) {
> +            av_log(s, AV_LOG_ERROR, "Blocking url with differnt origin\n");
> +            return AVERROR(EIO);
> +        }
> +        if (s->same_origin_check == AVFMT_SAME_ORIGIN_CHECK_PATH &&
> +            av_strnstr(url + len, "/../", uc.query - end)) {
> +            av_log(s, AV_LOG_ERROR, "Blocking url tricks\n");
> +            return AVERROR(EIO);
> +        }
> +    }
> +
>       return ffio_open_whitelist(pb, url, flags, &s->interrupt_callback, options, s->protocol_whitelist, s->protocol_blacklist);
>   }
>   
> diff --git a/libavformat/options_table.h b/libavformat/options_table.h
> index 86d836cfeb..da788164f1 100644
> --- a/libavformat/options_table.h
> +++ b/libavformat/options_table.h
> @@ -106,6 +106,9 @@ static const AVOption avformat_options[] = {
>   {"max_streams", "maximum number of streams", OFFSET(max_streams), AV_OPT_TYPE_INT, { .i64 = 1000 }, 0, INT_MAX, D },
>   {"skip_estimate_duration_from_pts", "skip duration calculation in estimate_timings_from_pts", OFFSET(skip_estimate_duration_from_pts), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, D},
>   {"max_probe_packets", "Maximum number of packets to probe a codec", OFFSET(max_probe_packets), AV_OPT_TYPE_INT, { .i64 = 2500 }, 0, INT_MAX, D },
> +{"same_origin", "same origin check", OFFSET(same_origin_check)    , AV_OPT_TYPE_INT  , { .i64 = AVFMT_SAME_ORIGIN_CHECK_PATH }, 0, INT_MAX, D|E, "same_origin"},
> +{"same_host"  , "same protocol, host, port, auth", 0              , AV_OPT_TYPE_CONST, { .i64 = AVFMT_SAME_ORIGIN_CHECK_HOST }, 0, INT_MAX, D|E, "same_origin"},
> +{"same_path"  , "same protocol, host, port, auth, parent path", 0 , AV_OPT_TYPE_CONST, { .i64 = AVFMT_SAME_ORIGIN_CHECK_PATH }, 0, INT_MAX, D|E, "same_origin"},

Missing NONE const? And do we want check_path to be default? It's a 
change in behavior.

>   {NULL},
>   };
>   
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