[Dnsmasq-discuss] /etc/hosts char length limit bug

[Matthias Andree]

Brandon,

I tried reproducing this from your description and failed.

Please provide your dnsmasq configuration, how it was built (patches to 
sources, make arguments), your hosts file, and recompile with proper 
debug symbols and possibly -fsanitize=address to obtain line numbers for 
the crash you're showing - and ideally you provoke the crash with a 
debugger attached, for instance, gdb --args dnsmasq -d [-other -opts] 
and then "run", and "backtrace full" once it has crashed.

I have added one long /etc/hosts line and dnsmasq v2.92 (2.92rel2 
doesn't seem to be in Git) and v2.93 do not crash for me.

Regards,
Matthias


Am 03.06.26 um 23:39 schrieb brandon via Dnsmasq-discuss:
> 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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