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sd-dhcp-server: clear out expired leases when processing requests

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The DHCP server configuration supports setting a maximum lease time, but old
leases are never actually cleared out if the client doesn't send a RELEASE.
This causes the pool to run out of addresses on networks where clients just
disappear, which is a fairly common occurrence on wireless networks.

Fix this by cleaning up expired leases before processing client requests, so
addresses can be reused for new clients.
This commit is contained in:
Toke Høiland-Jørgensen 2021-10-28 22:36:51 +02:00
parent ff8b7bd6a0
commit d635a7f9e4
1 changed files with 25 additions and 0 deletions
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25
src/libsystemd-network/sd-dhcp-server.c
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@ -854,6 +854,27 @@ static int prepare_new_lease(
return 0;
}
static int dhcp_server_cleanup_expired_leases(sd_dhcp_server *server) {
DHCPLease *lease;
usec_t time_now;
int r;
assert(server);
r = sd_event_now(server->event, clock_boottime_or_monotonic(), &time_now);
if (r < 0)
return r;
HASHMAP_FOREACH(lease, server->bound_leases_by_client_id) {
if (lease->expiration < time_now) {
log_dhcp_server(server, "CLEAN (0x%x)", be32toh(lease->address));
dhcp_lease_free(lease);
}
}
return 0;
}
#define HASH_KEY SD_ID128_MAKE(0d,1d,fe,bd,f1,24,bd,b3,47,f1,dd,6e,73,21,93,30)
int dhcp_server_handle_message(sd_dhcp_server *server, DHCPMessage *message, size_t length) {
@ -883,6 +904,10 @@ int dhcp_server_handle_message(sd_dhcp_server *server, DHCPMessage *message, siz
/* this only fails on critical errors */
return r;
r = dhcp_server_cleanup_expired_leases(server);
if (r < 0)
return r;
existing_lease = hashmap_get(server->bound_leases_by_client_id, &req->client_id);
static_lease = hashmap_get(server->static_leases_by_client_id, &req->client_id);