Using instructions at https://askubuntu.com/questions/41610/how-do-i-rebuild-a-package-to-include-debugging-information built a package with working debug symbols.


(gdb) bt
#0  0x00007f21c90499fc in pthread_kill () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00007f21c8ff5476 in raise () from /lib/x86_64-linux-gnu/libc.so.6
#2  0x00007f21c8fdb7f3 in abort () from /lib/x86_64-linux-gnu/libc.so.6
#3  0x00007f21c903c676 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#4  0x00007f21c9053cfc in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#5  0x00007f21c9055a54 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#6  0x00007f21c9058453 in free () from /lib/x86_64-linux-gnu/libc.so.6
#7  0x000055ea8f653810 in dhcp_netid_free (nid=0x8000000ba) at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/option.c:1333
#8  0x000055ea8f6538df in dhcp_netid_list_free (netid=0x0) at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/option.c:1363
#9  0x000055ea8f653956 in dhcp_config_free (config=0x55ea90bc0050)
    at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/option.c:1381
#10 0x000055ea8f661868 in clear_dynamic_conf () at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/option.c:5777
#11 0x000055ea8f661947 in reread_dhcp () at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/option.c:5818
#12 0x000055ea8f6737b7 in clear_cache_and_reload (now=1709322392)
    at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/dnsmasq.c:1738
#13 0x000055ea8f672db5 in async_event (pipe=17, now=1709322392)
    at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/dnsmasq.c:1482
#14 0x000055ea8f6725aa in main (argc=17, argv=0x7ffe73b7b4c8)
    at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/dnsmasq.c:1224

(gdb) frame 9
#9  0x000055ea8f653956 in dhcp_config_free (config=0x55ea90bc0050)
    at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/option.c:1381
1381	in /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/option.c
(gdb) p *config->netid->list
$17 = {net = 0x55efce12bef0 <error: Cannot access memory at address 0x55efce12bef0>, next = 0xa03b9e2eb1d772d3}
(gdb) p *config->netid->list->next
Cannot access memory at address 0xa03b9e2eb1d772d3

(gdb) frame 10
#10 0x000055ea8f661868 in clear_dynamic_conf () at /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/option.c:5777
5777	in /home/ubuntu/dnsmasq/dnsmasq-2.90/debian/build/no-lua/option.c
(gdb) info locals
configs = 0x55ea90bc0050
cp = 0x55ea90bbd220
up = 0x55ea90baefd8
(gdb) p *cp
$19 = {flags = 2096, clid_len = 0, clid = 0x0, hostname = 0x55ea90bbd2c0 "host-10-1-0-7", domain = 0x55ea90bbd2ce "openstacklocal", 
  netid = 0x55ea90bbd2f0, filter = 0x0, addr6 = 0x0, addr = {s_addr = 117440778}, decline_time = 0, lease_time = 0, 
  hwaddr = 0x55ea90bbd290, next = 0x55ea90bbd0f0}
(gdb) p *configs
$20 = {flags = 2096, clid_len = 0, clid = 0x0, hostname = 0x55ea90bc00c0 "host-10-1-0-62", 
  domain = 0x55ea90bc00cf "openstacklocal", netid = 0x55ea90bc00f0, filter = 0x0, addr6 = 0x0, addr = {s_addr = 1040187658}, 
  decline_time = 0, lease_time = 0, hwaddr = 0x55ea90bbd370, next = 0x55ea90bbd220}
(gdb) p *configs->netid
$21 = {list = 0x55ea90bc0110, next = 0x0}
(gdb) p *configs->netid->list
$22 = {net = 0x55efce12bef0 <error: Cannot access memory at address 0x55efce12bef0>, next = 0xa03b9e2eb1d772d3}
(gdb) p *cp->netid->list
$23 = {net = 0x55ea90bbd330 "port-f3c2ed23-d032-40ec-bd9e-55b1f0fe22f4", next = 0x7ffe73b7af00}

There happens some memory corruption, but hard to say what might be its cause. Not yet clear to me.