libnetwork: check DNS loopback with user DNS opts#44976
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corhere merged 1 commit intomoby:masterfrom Feb 14, 2023
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DNS servers in the loopback address range should always be resolved in the host network namespace when the servers are configured by reading from the host's /etc/resolv.conf. The daemon mistakenly conflated the presence of DNS options (docker run --dns-opt) with user-supplied DNS servers, treating the list of servers loaded from the host as a user- supplied list and attempting to resolve in the container's network namespace. Correct this oversight so that loopback DNS servers are only resolved in the container's network namespace when the user provides the DNS server list, irrespective of other DNS configuration. Signed-off-by: Cory Snider <csnider@mirantis.com>
neersighted
approved these changes
Feb 11, 2023
This was referenced Jan 19, 2024
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--dns-optbreaks resolving of external names by internal DNS server docker/for-linux#1404systemd-resolved#43705- What I did
DNS servers in the loopback address range should always be resolved in the host network namespace when the servers are configured by reading from the host's /etc/resolv.conf. The daemon mistakenly conflated the presence of DNS options (
docker run --dns-opt) with user-supplied DNS servers, treating the list of servers loaded from the host as a user- supplied list and attempting to resolve in the container's network namespace. Correct this oversight so that loopback DNS servers are only resolved in the container's network namespace when the user provides the DNS server list, irrespective of other DNS configuration.- How I did it
Should be self-explanatory.
- How to verify it
Run a daemon on a host with DNS resolved by systemd-resolved or some other configuration with loopback-to-localhost DNS resolution. Run a container attached to a user-defined network with some
--dns-optflag and verify that DNS resolves within the container.- Description for the changelog
--dns-optor--dns-searchflags and systemd-resolved is used for DNS resolution on the host.- A picture of a cute animal (not mandatory but encouraged)