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udpsrc: Disable allocated port reuse for unicast

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The `reuse` property end up setting the SO_REUSEADDR socket option for
the UDP socket. This setting have surprising effects.

On Linux systems the man page (`socket(7)`) states:
```
SO_REUSEADDR
    Indicates that the rules used in validating addresses supplied
    in a bind(2) call should allow reuse of local addresses. For
    AF_INET sockets this means that a socket may bind, except when
    there is an active listening socket bound to the address.
```

But since UDP does not listen this ends up meaning that when an
ephemeral port is allocated (setting the `port` to `0`) the kernel is
free to reuse any other UDP port that has `SO_REUSEADDR` set.

Tests checking the likelyhood of port conflict when using multiple
`udpsrc` shows port conflicts starting to occur after ~100-300 udpsrc
with port allocation enabled. See issue #3411 for more details.

Changing the default value of a property is not a small thing we risk
breaking application that rely on the current default value. But since
the effects of having `reuse` default `TRUE` on can also have damaging
and hard-to-debug consequences, it might be worth to consider.

Having `SO_REUSEADDR` enabled for multicast, might have some use cases
but for unicast, with dynamic port allocation, it does not make sense.

When not using an multicast address we will disable port reuse if the
`port` property is set to 0 (=allocate) and warn the user that we did
so.

Closes #3411

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7841>
This commit is contained in:
Jonas K Danielsson 2024-05-29 06:33:50 +02:00 committed by GStreamer Marge Bot
parent 75fcfdb12d
commit 20e3454c26
1 changed files with 10 additions and 1 deletions
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11
subprojects/gst-plugins-good/gst/udp/gstudpsrc.c
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@ -1589,6 +1589,7 @@ gst_udpsrc_open (GstUDPSrc * src)
GInetAddress *addr, *bind_addr;
GSocketAddress *bind_saddr;
GError *err = NULL;
gboolean allow_port_reuse = src->reuse;
if (src->source_addrs) {
g_list_free_full (src->source_addrs, (GDestroyNotify) g_object_unref);
@ -1632,7 +1633,15 @@ gst_udpsrc_open (GstUDPSrc * src)
bind_saddr = g_inet_socket_address_new (bind_addr, src->port);
g_object_unref (bind_addr);
if (!g_socket_bind (src->used_socket, bind_saddr, src->reuse, &err)) {
if (allow_port_reuse && src->port == 0
&& !g_inet_address_get_is_multicast (addr)) {
GST_WARNING_OBJECT (src,
"Disabling port reuse for dynamically allocated port to avoid potential conflicts");
allow_port_reuse = FALSE;
}
if (!g_socket_bind (src->used_socket, bind_saddr, allow_port_reuse, &err)) {
GST_ERROR_OBJECT (src, "%s: error binding to %s:%d", err->message,
src->address, src->port);
goto bind_error;