From d635a7f9e4c58c5578f4fe2989bb799325067232 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= Date: Thu, 28 Oct 2021 22:36:51 +0200 Subject: [PATCH 1/2] sd-dhcp-server: clear out expired leases when processing requests 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. --- src/libsystemd-network/sd-dhcp-server.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/src/libsystemd-network/sd-dhcp-server.c b/src/libsystemd-network/sd-dhcp-server.c index 45ac70b461..39ac5e86fa 100644 --- a/src/libsystemd-network/sd-dhcp-server.c +++ b/src/libsystemd-network/sd-dhcp-server.c @@ -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); From cb3c06a02eea17999c4fd577d35be7c9d1745a91 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= Date: Fri, 29 Oct 2021 12:24:33 +0200 Subject: [PATCH 2/2] sd-dhcp-server: fix address availability checks The checks for finding a new available address in the pool were broken in two ways: not using UINT32_TO_PTR() on hashmap lookups resulted in false negatives, and the check wasn't skipping the server address if that was part of the pool. Move the check for available addresses to a small helper function and fix both issues, and also add a check to the REQUEST code for the server address. --- src/libsystemd-network/sd-dhcp-server.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/src/libsystemd-network/sd-dhcp-server.c b/src/libsystemd-network/sd-dhcp-server.c index 39ac5e86fa..604c34fe15 100644 --- a/src/libsystemd-network/sd-dhcp-server.c +++ b/src/libsystemd-network/sd-dhcp-server.c @@ -875,6 +875,17 @@ static int dhcp_server_cleanup_expired_leases(sd_dhcp_server *server) { return 0; } +static bool address_available(sd_dhcp_server *server, be32_t address) { + assert(server); + + if (hashmap_contains(server->bound_leases_by_address, UINT32_TO_PTR(address)) || + hashmap_contains(server->static_leases_by_address, UINT32_TO_PTR(address)) || + address == server->address) + return false; + + return true; +} + #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) { @@ -943,8 +954,7 @@ int dhcp_server_handle_message(sd_dhcp_server *server, DHCPMessage *message, siz be32_t tmp_address; tmp_address = server->subnet | htobe32(server->pool_offset + (hash + i) % server->pool_size); - if (!hashmap_contains(server->bound_leases_by_address, &tmp_address) && - !hashmap_contains(server->static_leases_by_address, &tmp_address)) { + if (address_available(server, tmp_address)) { address = tmp_address; break; } @@ -1021,6 +1031,10 @@ int dhcp_server_handle_message(sd_dhcp_server *server, DHCPMessage *message, siz address = req->message->ciaddr; } + /* disallow our own address */ + if (address == server->address) + return 0; + pool_offset = get_pool_offset(server, address); existing_lease_by_address = hashmap_get(server->bound_leases_by_address, UINT32_TO_PTR(address));