Hello DNS Masq,

While using dnsmasq as part of libvirt I've noticed that my /etc/hosts prevents 
my VMs from starting. I looked through the system logs and found that it was 
DNS Masq that was crashing causing my VMs to not have any network (not even 
DHCP or any ip connectivity).

I'm using NixOS and using StevenBlack hosts to block ads on my system.

I sorted /etc/hosts lines by length and then performed a binary search to cut 
down the longest lines one by one.


What I found was that once the lines get to <=57 chars dnsmasq is able to start 
with no problems.



Please see my change log here for what I've done on my system:
https://github.com/StevenBlack/hosts/compare/master...yuannan:hosts:short 


Versions:
- dnsmasq: dnsmasq-2.92rel2
- nixos: NixOS 26.11 (Zokor) x86_64
- kernel: Linux 7.0.10-zen1 x86_64
- libvirt: 12.2.0

Logs:
```Jun 03 22:21:07 aurelius systemd-coredump[326471]: [🡕] Process 326466 
(dnsmasq) of user 65534 dumped core.
                                                  

                                                   Module 
/nix/store/s6fgvggs1rh0qq88z64xp2ais3kq19m7-dnsmasq-2.92rel2/bin/dnsmasq 
without build-id.

                                                   Module libncursesw.so.6 
without build-id.

                                                   Module libedit.so.0 without 
build-id.

                                                   Module libjansson.so.4 
without build-id.

                                                   Module libxtables.so.12 
without build-id.

                                                   Module libnftnl.so.11 
without build-id.

                                                   Module libmnl.so.0 without 
build-id.

                                                   Module libnftables.so.1 
without build-id.

                                                   Module libgmp.so.10 without 
build-id.

                                                   Module libhogweed.so.6 
without build-id.

                                                   Module libnettle.so.8 
without build-id.

                                                   Module libnfnetlink.so.0 
without build-id.

                                                   Module 
libnetfilter_conntrack.so.3 without build-id.

                                                   Module libidn.so.12 without 
build-id.

                                                   Stack trace of thread 326466:

                                                   #0  0x00007351cf89fdcc 
__pthread_kill_implementation (libc.so.6 + 0x9fdcc)

                                                   #1  0x00007351cf84265e raise 
(libc.so.6 + 0x4265e)

                                                   #2  0x00007351cf829350 abort 
(libc.so.6 + 0x29350)

                                                   #3  0x00007351cf82a3c8 
__libc_message_impl.cold (libc.so.6 + 0x2a3c8)

                                                   #4  0x00007351cf931b79 
__fortify_fail (libc.so.6 + 0x131b79)

                                                   #5  0x00007351cf931444 
__chk_fail (libc.so.6 + 0x131444)

                                                   #6  0x00007351cf933193 
__strcpy_chk (libc.so.6 + 0x133193)

                                                   #7  0x000064cc6d9f669a 
read_hostsfile 
(/nix/store/s6fgvggs1rh0qq88z64xp2ais3kq19m7-dnsmasq-2.92rel2/bin/dnsmasq + 
0xf69a)

                                                   #8  0x000064cc6d9f6caf 
cache_reload 
(/nix/store/s6fgvggs1rh0qq88z64xp2ais3kq19m7-dnsmasq-2.92rel2/bin/dnsmasq + 
0xfcaf)

                                                   #9  0x000064cc6da19a1d 
clear_cache_and_reload 
(/nix/store/s6fgvggs1rh0qq88z64xp2ais3kq19m7-dnsmasq-2.92rel2/bin/dnsmasq + 
0x32a1d)

                                                   #10 0x000064cc6d9f36b8 main 
(/nix/store/s6fgvggs1rh0qq88z64xp2ais3kq19m7-dnsmasq-2.92rel2/bin/dnsmasq + 
0xc6b8)

                                                   #11 0x00007351cf82b285 
__libc_start_call_main (libc.so.6 + 0x2b285)

                                                   #12 0x00007351cf82b338 
__libc_start_main@@GLIBC_2.34 (libc.so.6 + 0x2b338)

                                                   #13 0x000064cc6d9f4245 
_start 
(/nix/store/s6fgvggs1rh0qq88z64xp2ais3kq19m7-dnsmasq-2.92rel2/bin/dnsmasq + 
0xd245)

                                                   ELF object binary 
architecture: AMD x86-64

```

Please let me know if there is anything else you need from me, thanks.


Brandon Lin

Managing Director - Emergence Technologies Ltd

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