I found this bug report after experiencing the same problem. The error message I got was exactly the same as the one in comment #2. The fix suggested by Kazuhiro in comment #9 fixed the problem.
I think that since this bug affects more than one person, it's not merely a problem with one person's local environment. I didn't have occasion to use KVM between 2024-02-27 and today, but it was working for me before then and I didn't manually change anything in my environment. I don't know enough about Ubuntu networking to say whether it's a bug in dnsmasq or another component, but surely a package upgrade shouldn't break something like this. $ cat /var/log/apt/history.log.1 (snip) Start-Date: 2024-02-27 06:19:38 Commandline: /usr/bin/unattended-upgrade Upgrade: dnsmasq-base:amd64 (2.89-1, 2.90-0ubuntu0.23.10.1) End-Date: 2024-02-27 06:19:42 (snip) $ cat /etc/issue Ubuntu 23.10 \n \l $ virsh --version 9.6.0 $ /usr/sbin/dnsmasq --version Dnsmasq version 2.90 Copyright (c) 2000-2024 Simon Kelley Compile time options: IPv6 GNU-getopt DBus no-UBus i18n IDN2 DHCP DHCPv6 no-Lua TFTP conntrack ipset nftset auth cryptohash DNSSEC loop-detect inotify dumpfile This software comes with ABSOLUTELY NO WARRANTY. Dnsmasq is free software, and you are welcome to redistribute it under the terms of the GNU General Public License, version 2 or 3 $ -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to dnsmasq in Ubuntu. https://bugs.launchpad.net/bugs/2055776 Title: After updating ubuntu, the network to which the subnet address is assigned does not become active in KVM. Status in dnsmasq package in Ubuntu: Invalid Bug description: phenomenon: After updating ubuntu, the network to which the subnet address is assigned does not become active in KVM. Cause: This is because the following dnsmasq update operation performed by apt's automatic update causes an error. It worked properly with dnsmasq 2.80, but does not work properly with 2.90. $ cat /var/log/apt/history.log (snip) Start-Date: 2024-02-27 06:17:31 Commandline: /usr/bin/unattended-upgrade Upgrade: dnsmasq-base:amd64 (2.80-1.1ubuntu1.7, 2.90-0ubuntu0.20.04.1) End-Date: 2024-02-27 06:17:44 (snip) $ Cause details: As a premise, bind-dynamic is set in the dnsmasq config file for KVM. Below is an example. $ cat default.conf ##WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE ##OVERWRITTEN AND LOST. Changes to this configuration should be made using: ## virsh net-edit default ## or other application using the libvirt API. ## ## dnsmasq conf file created by libvirt strict-order user=libvirt-dnsmasq pid-file=/run/libvirt/network/default.pid except-interface=lo bind-dynamic interface=virbr0 dhcp-range=192.168.122.2,192.168.122.254,255.255.255.0 dhcp-no-override dhcp-authoritative dhcp-lease-max=253 dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts $ When starting the network with KVM (virsh net-start), dnsmasq started from KVM executes the make_sock function twice as shown below. $ cat network.c (snip) 1087 static struct listener *create_listeners(union mysockaddr *addr, int do_ 1087 tftp, int dienow) 1088 { 1089 struct listener *l = NULL; 1090 int fd = -1, tcpfd = -1, tftpfd = -1; 1091 1092 (void)do_tftp; 1093 1094 if (daemon->port != 0) 1095 { 1096 fd = make_sock(addr, SOCK_DGRAM, dienow); 1097 tcpfd = make_sock(addr, SOCK_STREAM, dienow); 1098 } (snip) The following code causes an issue with the update made in dnsmasq 2.90. $ cat network.c (snip) 895 static int make_sock(union mysockaddr *addr, int type, int dienow) 896 { (snip) 934 if (!option_bool(OPT_CLEVERBIND) || errno != EADDRNOTAVAIL) 935 { 936 if (dienow) 937 die(s, daemon->addrbuff, EC_BADNET); 938 else 939 my_syslog(LOG_WARNING, s, daemon->addrbuff, strerror(errno)) 939 ; 940 } (snip) function "make_sock" in network.c:1096 binds the socket to 192.168.122.1/24, and then make_sock in network.c:1097 tries to bind to the same address. However, in network.c:934, when errno==98 occurs, network.c:937 is executed, so dnsmasq does not cause a startup error. As a result, virsh net-start fails. As a temporary workaround, it will work if you try not to die. $ diff -u network_c_back network.c --- network_c_back 2024-02-29 15:36:05.156467935 +0000 +++ network.c 2024-02-29 15:36:38.733324350 +0000 @@ -934,7 +934,8 @@ if (!option_bool(OPT_CLEVERBIND) || errno != EADDRNOTAVAIL) { if (dienow) - die(s, daemon->addrbuff, EC_BADNET); + my_syslog(LOG_WARNING, s, daemon->addrbuff, strerror(errno)); + //die(s, daemon->addrbuff, EC_BADNET); else my_syslog(LOG_WARNING, s, daemon->addrbuff, strerror(errno)); } $ If bind-dynamic is set, it should be modified so that it works even if errno==98. For reference, in the case of dnsmasq 2.80, the code is as follows, so no error occurs. network.c 699 static int make_sock(union mysockaddr *addr, int type, int dienow) 700 { 701 int family = addr->sa.sa_family; 702 int fd, rc, opt = 1; (snip) 715 err: 716 errsave = errno; 717 port = prettyprint_addr(addr, daemon->addrbuff); 718 if (!option_bool(OPT_NOWILD) && !option_bool(OPT_CLEVERBIND)) 719 sprintf(daemon->addrbuff, "port %d", port); 720 s = _("failed to create listening socket for %s: %s"); 721 722 if (fd != -1) 723 close (fd); 724 725 errno = errsave; 726 727 if (dienow) 728 { 729 /* failure to bind addresses given by --listen-address at this 729 point 730 is OK if we're doing bind-dynamic */ 731 if (!option_bool(OPT_CLEVERBIND)) 732 die(s, daemon->addrbuff, EC_BADNET); 733 } 734 else 735 my_syslog(LOG_WARNING, s, daemon->addrbuff, strerror(errno)); 736 737 return -1; 738 } If bind-dynamic is set (option_bool(OPT_CLEVERBIND)==true), it will not die. 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