1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
2
3 #include "resolved-socket-graveyard.h"
4
5 #define SOCKET_GRAVEYARD_USEC (5 * USEC_PER_SEC)
6 #define SOCKET_GRAVEYARD_MAX 100
7
8 /* This implements a socket "graveyard" for UDP sockets. If a socket fd is added to the graveyard it is kept
9 * open for a couple of more seconds, expecting one reply. Once the reply is received the fd is closed
10 * immediately, or if none is received it is closed after the timeout. Why all this? So that if we contact a
11 * DNS server, and it doesn't reply instantly, and we lose interest in the response and thus close the fd, we
12 * don't end up sending back an ICMP error once the server responds but we aren't listening anymore. (See
13 * https://github.com/systemd/systemd/issues/17421 for further information.)
14 *
15 * Note that we don't allocate any timer event source to clear up the graveyard once the socket's timeout is
16 * reached. Instead we operate lazily: we close old entries when adding a new fd to the graveyard, or
17 * whenever any code runs manager_socket_graveyard_process() — which the DNS transaction code does right
18 * before allocating a new UDP socket. */
19
socket_graveyard_free(SocketGraveyard * g)20 static SocketGraveyard* socket_graveyard_free(SocketGraveyard *g) {
21 if (!g)
22 return NULL;
23
24 if (g->manager) {
25 assert(g->manager->n_socket_graveyard > 0);
26 g->manager->n_socket_graveyard--;
27
28 if (g->manager->socket_graveyard_oldest == g)
29 g->manager->socket_graveyard_oldest = g->graveyard_prev;
30
31 LIST_REMOVE(graveyard, g->manager->socket_graveyard, g);
32
33 assert((g->manager->n_socket_graveyard > 0) == !!g->manager->socket_graveyard);
34 assert((g->manager->n_socket_graveyard > 0) == !!g->manager->socket_graveyard_oldest);
35 }
36
37 if (g->io_event_source) {
38 log_debug("Closing graveyard socket fd %i", sd_event_source_get_io_fd(g->io_event_source));
39 sd_event_source_disable_unref(g->io_event_source);
40 }
41
42 return mfree(g);
43 }
44
45 DEFINE_TRIVIAL_CLEANUP_FUNC(SocketGraveyard*, socket_graveyard_free);
46
manager_socket_graveyard_process(Manager * m)47 void manager_socket_graveyard_process(Manager *m) {
48 usec_t n = USEC_INFINITY;
49
50 assert(m);
51
52 while (m->socket_graveyard_oldest) {
53 SocketGraveyard *g = m->socket_graveyard_oldest;
54
55 if (n == USEC_INFINITY)
56 assert_se(sd_event_now(m->event, CLOCK_BOOTTIME, &n) >= 0);
57
58 if (g->deadline > n)
59 break;
60
61 socket_graveyard_free(g);
62 }
63 }
64
manager_socket_graveyard_clear(Manager * m)65 void manager_socket_graveyard_clear(Manager *m) {
66 assert(m);
67
68 while (m->socket_graveyard)
69 socket_graveyard_free(m->socket_graveyard);
70 }
71
on_io_event(sd_event_source * s,int fd,uint32_t revents,void * userdata)72 static int on_io_event(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
73 SocketGraveyard *g = userdata;
74
75 assert(g);
76
77 /* An IO event happened on the graveyard fd. We don't actually care which event that is, and we don't
78 * read any incoming packet off the socket. We just close the fd, that's enough to not trigger the
79 * ICMP unreachable port event */
80
81 socket_graveyard_free(g);
82 return 0;
83 }
84
manager_socket_graveyard_make_room(Manager * m)85 static void manager_socket_graveyard_make_room(Manager *m) {
86 assert(m);
87
88 while (m->n_socket_graveyard >= SOCKET_GRAVEYARD_MAX)
89 socket_graveyard_free(m->socket_graveyard_oldest);
90 }
91
manager_add_socket_to_graveyard(Manager * m,int fd)92 int manager_add_socket_to_graveyard(Manager *m, int fd) {
93 _cleanup_(socket_graveyard_freep) SocketGraveyard *g = NULL;
94 int r;
95
96 assert(m);
97 assert(fd >= 0);
98
99 manager_socket_graveyard_process(m);
100 manager_socket_graveyard_make_room(m);
101
102 g = new(SocketGraveyard, 1);
103 if (!g)
104 return log_oom();
105
106 *g = (SocketGraveyard) {
107 .manager = m,
108 };
109
110 LIST_PREPEND(graveyard, m->socket_graveyard, g);
111 if (!m->socket_graveyard_oldest)
112 m->socket_graveyard_oldest = g;
113
114 m->n_socket_graveyard++;
115
116 assert_se(sd_event_now(m->event, CLOCK_BOOTTIME, &g->deadline) >= 0);
117 g->deadline += SOCKET_GRAVEYARD_USEC;
118
119 r = sd_event_add_io(m->event, &g->io_event_source, fd, EPOLLIN, on_io_event, g);
120 if (r < 0)
121 return log_error_errno(r, "Failed to create graveyard IO source: %m");
122
123 r = sd_event_source_set_io_fd_own(g->io_event_source, true);
124 if (r < 0)
125 return log_error_errno(r, "Failed to enable graveyard IO source fd ownership: %m");
126
127 (void) sd_event_source_set_description(g->io_event_source, "graveyard");
128
129 log_debug("Added socket %i to graveyard", fd);
130
131 TAKE_PTR(g);
132 return 0;
133 }
134