Commit message: ffserver: Check chunk size

Fixes out of array access

Fixes: poc_ffserver.py
Found-by: Paul Cher <paulcher@icloud.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
CVE: CVE-2016-10192
CWE: CWE-119
Vulnerability description: Heap-based buffer overflow in ffserver.c in FFmpeg before 2.8.10, 3.0.x before 3.0.5, 3.1.x before 3.1.6, and 3.2.x before 3.2.2 allows remote attackers to execute arbitrary code by leveraging failure to check chunk size.

Project: FFmpeg
File: ffserver.c

static int http_receive_data(HTTPContext *c)
{
    HTTPContext *c1;
    int len, loop_run = 0;

    while (c->chunked_encoding && !c->chunk_size &&
           c->buffer_end > c->buffer_ptr) {
        /* read chunk header, if present */
        len = recv(c->fd, c->buffer_ptr, 1, 0);

        if (len < 0) {
            if (ff_neterrno() != AVERROR(EAGAIN) &&
                ff_neterrno() != AVERROR(EINTR))
                /* error : close connection */
                goto fail;
            return 0;
        } else if (len == 0) {
            /* end of connection : close it */
            goto fail;
         } else if (c->buffer_ptr - c->buffer >= 2 &&
                    !memcmp(c->buffer_ptr - 1, "\r\n", 2)) {
             c->chunk_size = strtol(c->buffer, 0, 16);
            if (c->chunk_size <= 0) { // end of stream or invalid chunk size
                c->chunk_size = 0;
                 goto fail;
            }
             c->buffer_ptr = c->buffer;
             break;
         } else if (++loop_run > 10)
            /* no chunk header, abort */
            goto fail;
        else
            c->buffer_ptr++;
    }

    if (c->buffer_end > c->buffer_ptr) {
        len = recv(c->fd, c->buffer_ptr,
                   FFMIN(c->chunk_size, c->buffer_end - c->buffer_ptr), 0);
        if (len < 0) {
            if (ff_neterrno() != AVERROR(EAGAIN) &&
                ff_neterrno() != AVERROR(EINTR))
                /* error : close connection */
                goto fail;
        } else if (len == 0)
             /* end of connection : close it */
             goto fail;
         else {
            av_assert0(len <= c->chunk_size);
             c->chunk_size -= len;
             c->buffer_ptr += len;
             c->data_count += len;
            update_datarate(&c->datarate, c->data_count);
        }
    }

    if (c->buffer_ptr - c->buffer >= 2 && c->data_count > FFM_PACKET_SIZE) {
        if (c->buffer[0] != 'f' ||
            c->buffer[1] != 'm') {
            http_log("Feed stream has become desynchronized -- disconnecting\n");
            goto fail;
        }
    }

    if (c->buffer_ptr >= c->buffer_end) {
        FFServerStream *feed = c->stream;
        /* a packet has been received : write it in the store, except
         * if header */
        if (c->data_count > FFM_PACKET_SIZE) {
            /* XXX: use llseek or url_seek
             * XXX: Should probably fail? */
            if (lseek(c->feed_fd, feed->feed_write_index, SEEK_SET) == -1)
                http_log("Seek to %"PRId64" failed\n", feed->feed_write_index);

            if (write(c->feed_fd, c->buffer, FFM_PACKET_SIZE) < 0) {
                http_log("Error writing to feed file: %s\n", strerror(errno));
                goto fail;
            }

            feed->feed_write_index += FFM_PACKET_SIZE;
            /* update file size */
            if (feed->feed_write_index > c->stream->feed_size)
                feed->feed_size = feed->feed_write_index;

            /* handle wrap around if max file size reached */
            if (c->stream->feed_max_size &&
                feed->feed_write_index >= c->stream->feed_max_size)
                feed->feed_write_index = FFM_PACKET_SIZE;

            /* write index */
            if (ffm_write_write_index(c->feed_fd, feed->feed_write_index) < 0) {
                http_log("Error writing index to feed file: %s\n",
                         strerror(errno));
                goto fail;
            }

            /* wake up any waiting connections */
            for(c1 = first_http_ctx; c1; c1 = c1->next) {
                if (c1->state == HTTPSTATE_WAIT_FEED &&
                    c1->stream->feed == c->stream->feed)
                    c1->state = HTTPSTATE_SEND_DATA;
            }
        } else {
            /* We have a header in our hands that contains useful data */
            AVFormatContext *s = avformat_alloc_context();
            AVIOContext *pb;
            AVInputFormat *fmt_in;
            int i;

            if (!s)
                goto fail;

            /* use feed output format name to find corresponding input format */
            fmt_in = av_find_input_format(feed->fmt->name);
            if (!fmt_in)
                goto fail;

            pb = avio_alloc_context(c->buffer, c->buffer_end - c->buffer,
                                    0, NULL, NULL, NULL, NULL);
            if (!pb)
                goto fail;

            pb->seekable = 0;

            s->pb = pb;
            if (avformat_open_input(&s, c->stream->feed_filename, fmt_in, NULL) < 0) {
                av_freep(&pb);
                goto fail;
            }

            /* Now we have the actual streams */
            if (s->nb_streams != feed->nb_streams) {
                avformat_close_input(&s);
                av_freep(&pb);
                http_log("Feed '%s' stream number does not match registered feed\n",
                         c->stream->feed_filename);
                goto fail;
            }

            for (i = 0; i < s->nb_streams; i++) {
                LayeredAVStream *fst = feed->streams[i];
                AVStream *st = s->streams[i];
                avcodec_parameters_to_context(fst->codec, st->codecpar);
                avcodec_parameters_from_context(fst->codecpar, fst->codec);
            }

            avformat_close_input(&s);
            av_freep(&pb);
        }
        c->buffer_ptr = c->buffer;
    }

    return 0;
 fail:
    c->stream->feed_opened = 0;
    close(c->feed_fd);
    /* wake up any waiting connections to stop waiting for feed */
    for(c1 = first_http_ctx; c1; c1 = c1->next) {
        if (c1->state == HTTPSTATE_WAIT_FEED &&
            c1->stream->feed == c->stream->feed)
            c1->state = HTTPSTATE_SEND_DATA_TRAILER;
    }
    return -1;
}