This bug was fixed in the package dnsmasq - 2.86-1.1ubuntu0.5
---------------
dnsmasq (2.86-1.1ubuntu0.5) jammy; urgency=medium
* src/dnsmasq.c: Fix a crash that can happen when an empty resolv.conf is
reloaded (LP: #2045570)
* src/helper.c: Fix wrong client address for dhcp-script when DHCPv4 relay
in use (LP: #2042587)
-- Andreas Hasenack <[email protected]> Thu, 11 Jan 2024 09:21:27
-0300
** Changed in: dnsmasq (Ubuntu Jammy)
Status: Fix Committed => Fix Released
--
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/2045570
Title:
dnsmasq crash when no servers in resolv.conf
Status in dnsmasq package in Ubuntu:
Fix Released
Status in dnsmasq source package in Jammy:
Fix Released
Bug description:
[ Impact ]
dnsmasq "keeps an eye" on /etc/resolv.conf, and reloads it whenever
the file is updated. When that happens and for some reason there were
no "nameserver" declarations in the updated file, dnsmasq can crash.
Here is a log of a reproducer:
$ dig +short @127.0.0.1 ubuntu.com
;; communications error to 127.0.0.1#53: timed out
;; communications error to 127.0.0.1#53: connection refused
;; communications error to 127.0.0.1#53: connection refused
;; no servers could be reached
We can see the startup, then when resolv.conf is read again and no
nameservers were found, and the crash:
Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: started, version 2.86
cachesize 150
Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: DNS service limited to local
subnets
Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: compile time options: IPv6
GNU-getopt DBus no-UBus i18n IDN2 DHCP DHCPv6 no-Lua TFTP conntrack ipset auth
cryptohash DNSSEC loop-detect inotify dumpfile
Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: reading /etc/resolv.conf
Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: using nameserver
10.0.100.1#53
Jan 03 13:57:13 j-dnsmasq-2045570 dnsmasq[1507]: read /etc/hosts - 7 addresses
Jan 03 13:57:13 j-dnsmasq-2045570 systemd[1]: Started dnsmasq - A lightweight
DHCP and caching DNS server.
Jan 03 13:58:01 j-dnsmasq-2045570 dnsmasq[1507]: no servers found in
/etc/resolv.conf, will retry
Jan 03 13:58:22 j-dnsmasq-2045570 systemd[1]: dnsmasq.service: Main process
exited, code=dumped, status=11/SEGV
Jan 03 13:58:22 j-dnsmasq-2045570 systemd[1]: dnsmasq.service: Failed with
result 'core-dump'.
dnsmasq has provisions for this situation, we can see that in the
13:58:01 message where it says it will retry, but due to this bug, it
crashes instead.
The problem was introduced[1] in version 2.86, and fixed in 2.87, so
only jammy is affected.
1.
https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=patch;h=d290630d31f4517ab26392d00753d1397f9a4114;hp=d2ad5dc073aaacaf22b117f16106282a73586803
The commit message says:
"""
This problem was introduced in 2.86.
"""
And indeed, I wasn't able to crash 2.80 shipped in focal.
[ Test Plan ]
It might take a few tries to reproduce the bug, but here is the general
outline. Also keep in mind that it's important to use a DNS name that isn't
cached already by a previous query.
# Create a jammy lxd container
lxc launch ubuntu-daily:jammy j-dnsmasq-2045570
# Enter the container
lxc shell j-dnsmasq-2045570
# From now on, all commands should be executed in the container.
# Install dnsmasq, and disable systemd-resolved
apt update && apt install -y dnsmasq
# Disable systemd-resolved, and start dnsmasq
systemctl disable --now systemd-resolved
systemctl enable --now dnsmasq
# In one terminal inside the container, watch the dnsmasq logs:
journalctl -u dnsmasq.service -f
# In another terminal, remove /etc/resolv.conf and create a new one, empty
rm /etc/resolv.conf
echo "nameserver 1.1.1.1" > /etc/resolv.conf
# restart dnsmasq
systemctl restart dnsmasq.service
# Perform a dns query
dig @127.0.0.1 +short linux.com
# Comment the namserver directive in resolv.conf
echo "#nameserver 1.1.1.1" > /etc/resolv.conf
# Observe in the dnsmasq logs that it notices the change with a
message like:
Jan 03 14:14:51 j-dnsmasq-2045570 dnsmasq[2274]: no servers found in
/etc/resolv.conf, will retry
# Perform a *different* DNS query
dig @127.0.0.1 +short ubuntu.com
# Observe in the dnsmasq logs that it crashes.
Jan 03 13:58:22 j-dnsmasq-2045570 systemd[1]: dnsmasq.service: Main process
exited, code=dumped, status=11/SEGV
Jan 03 13:58:22 j-dnsmasq-2045570 systemd[1]: dnsmasq.service: Failed with
result 'core-dump'.
If it doesn't crash right away, repeat these steps a few times, but using a
different domain name each time:
- add "nameserver 127.0.0.1" to /etc/resolv.conf
- observe that dnsmasq notices the change to the file
- perform a query for some random domain using "dig @127.0.0.1 +short
<domain-of-your-choosing>"
- remove "nameserver" from /etc/resolv.conf, observe that dnsmasq noticed the
change
- perform a query for another random domain
The fixed version from proposed will not crash. That last query with
no "nameserver" lines in resolv.conf won't work, but it won't crash
the server.
[ Where problems could occur ]
This is doing some pointer/memory manipulation that could introduce
memory leaks or other crashes. In fact, this is exactly what happened
in the 2.86 release, which, and I quote, "Major rewrite of the DNS
server and domain handling code. This should be largely transparent,
but it drastically improves performance and reduces memory foot-
print"[2]. 2.88 was then released with the fix used in this SRU (the
commit is also in the 2.87 tag, but the upstream release notes only
mention it in 2.88).
2.
https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob;f=CHANGELOG;h=2ce53a81079810ae43588607f43851dabb5db38d;hb=HEAD#l224
[ Other Info ]
Not at this time.
[ Original description ]
upstream discussion:
https://lists.thekelleys.org.uk/pipermail/dnsmasq-
discuss/2022q3/016563.html
in my journal, my dns service crash and restart just after:
Dec 04 17:18:38 dnsmasq[199333]: no servers found in
/run/NetworkManager/no-stub-resolv.conf, will retry
oops report: https://errors.ubuntu.com/oops/29cf5e2e-92b1-11ee-9bdf-
fa163ec44ecd
ubuntu jammy, dnsmasq-base 2.86-1.1ubuntu0.3
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/dnsmasq/+bug/2045570/+subscriptions
--
Mailing list: https://launchpad.net/~touch-packages
Post to : [email protected]
Unsubscribe : https://launchpad.net/~touch-packages
More help : https://help.launchpad.net/ListHelp
