From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Thu, 7 May 2026 03:19:25 +0000 (+0900)
Subject: dhcp-server-request: check server address in DHCPDECLINE and DHCPRELEASE
X-Git-Tag: v261-rc1~22^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d40d021ca5e2b178ac542c70052b6621e7baec97;p=thirdparty%2Fsystemd.git

dhcp-server-request: check server address in DHCPDECLINE and DHCPRELEASE

Otherwise, we may do something wrong by messages for another DHCP server.
Let's silently ignore messages with unmatching server identifier.

Also, logs something when we receive DHCPRELEASE but found lease does
not match the reported address.
---

diff --git a/src/libsystemd-network/dhcp-server-request.c b/src/libsystemd-network/dhcp-server-request.c
index 202a8b888cd..6ce68dab40d 100644
--- a/src/libsystemd-network/dhcp-server-request.c
+++ b/src/libsystemd-network/dhcp-server-request.c
@@ -364,10 +364,12 @@ static int dhcp_server_process_decline(sd_dhcp_server *server, DHCPRequest *req,
         assert(server);
         assert(req);
 
-        log_dhcp_server(server, "DECLINE (0x%x): %s", be32toh(req->message->xid), strna(error_message));
+        if (req->server_address != server->address)
+                return 0; /* The message is not for us. Let's silently ignore the packet. */
 
-        /* TODO: make sure we don't offer this address again */
+        /* TODO: make sure we don't offer this address again for a while. */
 
+        log_dhcp_server(server, "DECLINE (0x%x): %s", be32toh(req->message->xid), strna(error_message));
         return 0;
 }
 
@@ -375,19 +377,20 @@ static int dhcp_server_process_release(sd_dhcp_server *server, DHCPRequest *req)
         assert(server);
         assert(req);
 
-        log_dhcp_server(server, "RELEASE (0x%x)",
-                        be32toh(req->message->xid));
+        if (req->server_address != server->address)
+                return 0; /* The message is not for us. Let's silently ignore the packet. */
 
         sd_dhcp_server_lease *existing_lease = hashmap_get(server->bound_leases_by_client_id, &req->client_id);
         if (!existing_lease)
                 return 0;
 
         if (existing_lease->address != req->message->ciaddr)
-                return 0;
+                return -EBADMSG;
 
         sd_dhcp_server_lease_unref(existing_lease);
         dhcp_server_on_lease_change(server);
 
+        log_dhcp_server(server, "RELEASE (0x%x)", be32toh(req->message->xid));
         return 0;
 }