Re: [FFmpeg-devel] [PATCH 8/9] avformat/udp: Fix temporary buffer race

[Marton Balint <cus@passwd.hu>]

On Sun, 9 Jun 2024, Michael Niedermayer wrote:

> Fixes: CID1551679 Data race condition
> Fixes: CID1551687 Data race condition

How is this a data race? Concurrent reading and writing is not supported 
for UDP as far as I know.

Thanks,
Marton

>
> Sponsored-by: Sovereign Tech Fund
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
> libavformat/udp.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/libavformat/udp.c b/libavformat/udp.c
> index c1ebdd12220..fd4847eda71 100644
> --- a/libavformat/udp.c
> +++ b/libavformat/udp.c
> @@ -107,7 +107,8 @@ typedef struct UDPContext {
>     pthread_cond_t cond;
>     int thread_started;
> #endif
> -    uint8_t tmp[UDP_MAX_PKT_SIZE+4];
> +    uint8_t tmp_rx[UDP_MAX_PKT_SIZE+4];
> +    uint8_t tmp_tx[UDP_MAX_PKT_SIZE+4];
>     int remaining_in_dg;
>     char *localaddr;
>     int timeout;
> @@ -504,7 +505,7 @@ static void *circular_buffer_task_rx( void *_URLContext)
>            see "General Information" / "Thread Cancelation Overview"
>            in Single Unix. */
>         pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &old_cancelstate);
> -        len = recvfrom(s->udp_fd, s->tmp+4, sizeof(s->tmp)-4, 0, (struct sockaddr *)&addr, &addr_len);
> +        len = recvfrom(s->udp_fd, s->tmp_rx+4, sizeof(s->tmp_rx)-4, 0, (struct sockaddr *)&addr, &addr_len);
>         pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancelstate);
>         pthread_mutex_lock(&s->mutex);
>         if (len < 0) {
> @@ -516,7 +517,7 @@ static void *circular_buffer_task_rx( void *_URLContext)
>         }
>         if (ff_ip_check_source_lists(&addr, &s->filters))
>             continue;
> -        AV_WL32(s->tmp, len);
> +        AV_WL32(s->tmp_rx, len);
>
>         if (av_fifo_can_write(s->fifo) < len + 4) {
>             /* No Space left */
> @@ -532,7 +533,7 @@ static void *circular_buffer_task_rx( void *_URLContext)
>                 goto end;
>             }
>         }
> -        av_fifo_write(s->fifo, s->tmp, len + 4);
> +        av_fifo_write(s->fifo, s->tmp_rx, len + 4);
>         pthread_cond_signal(&s->cond);
>     }
>
> @@ -581,9 +582,9 @@ static void *circular_buffer_task_tx( void *_URLContext)
>         len = AV_RL32(tmp);
>
>         av_assert0(len >= 0);
> -        av_assert0(len <= sizeof(s->tmp));
> +        av_assert0(len <= sizeof(s->tmp_tx));
>
> -        av_fifo_read(s->fifo, s->tmp, len);
> +        av_fifo_read(s->fifo, s->tmp_tx, len);
>
>         pthread_mutex_unlock(&s->mutex);
>
> @@ -607,7 +608,7 @@ static void *circular_buffer_task_tx( void *_URLContext)
>             target_timestamp = start_timestamp + sent_bits * 1000000 / s->bitrate;
>         }
>
> -        p = s->tmp;
> +        p = s->tmp_tx;
>         while (len) {
>             int ret;
>             av_assert0(len > 0);
> -- 
> 2.45.2
>
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