add support for podman create/run --domainname #15200

cdoern · 2022-08-04T20:06:50Z

domainname functions similarly to --hostname, it sets the value in /etc/hosts
to whatever you speficy in conjunction with --hostname. so if you pass
--hostname=foo --domainmame=baz.net, /etc/hosts will get the combined entry and /proc/sys/kernel/domainname will get baz.net via a sysctl.

resolves #15102

Signed-off-by: Charlie Doern cdoern@redhat.com

Does this PR introduce a user-facing change?

introduce --domanname to podman create/run which allows users to set a domainname along with a hostname in their host files

Luap99

I took a quick look at docker and this doe snot match it.
The domain name is added in /etc/hosts and setdomainname()? Looks like they jusy use a sysctl for that: https://github.com/moby/moby/blob/master/daemon/oci_utils.go#L8

Also you are ignoring the compat API value and it must be added to podman container inspect.

cmd/podman/containers/create.go

pkg/specgen/generate/namespaces.go

giuseppe · 2022-08-05T21:29:29Z

I think the problem is with the /proc/sys/kernel/domainname file that is always owned by root in the initial user namespace, so writing to it always fails from a rootless user namespace, even if the value is namespaced.

I am not sure how the patch to crun can address it, have you verified it really writes to /proc/sys/kernel/domainname and that you can read the value back from /proc/sys/kernel/domainname within the container?

The correct fix IMO is to address it in the OCI specs and make domainname explicit as the hostname is.

The only possible workaround I see is to convert a write to kernel.domainname to a setdomainname(2), something like:

diff --git a/src/libcrun/linux.c b/src/libcrun/linux.c
index 5a7531e..4cd39e2 100644
--- a/src/libcrun/linux.c
+++ b/src/libcrun/linux.c
@@ -3255,6 +3255,14 @@ libcrun_set_sysctl (libcrun_container_t *container, libcrun_error_t *err)
       if (UNLIKELY (ret < 0))
         return ret;
 
+      if (strcmp (name, "kernel/domainname") == 0)
+        {
+          ret = setdomainname (def->linux->sysctl->values[i], strlen (def->linux->sysctl->values[i]));
+          if (UNLIKELY (ret < 0))
+            return crun_make_error (err, errno, "setdomainname");
+          continue;
+        }
+

I am fine to such a workaround if it unblocks you, but I still suggest to 1) verify your patch really does what it is supposed to do 2) propose a fix for the OCI runtime specs.

Also no need to block with rootless if it is not currently supported. Just skip the test.

cdoern · 2022-08-05T21:37:39Z

I agree with the OCI spec approach. I've been messing around with the crun hack all day and it doesn't seem to want to cooperate. I'll make a PR for the runtime spec on Monday.

rhatdan · 2022-08-06T11:26:08Z

Does this work with Docker? Perhaps only because docker daemon runs as root and running docker in rootless mode this would fail also?

mheon · 2022-08-06T16:48:31Z

Do we want to add the flag as root-only for now, and enable rootless support once the OCI spec PR merges and support actually lands in crun/runc?

cdoern · 2022-08-06T16:55:01Z

Do we want to add the flag as root-only for now, and enable rootless support once the OCI spec PR merges and support actually lands in crun/runc?

That sgtm, I haven't pushed the new version with the sysctl. I'll finish that up on Monday then take care of the spec PR

docs/source/markdown/options/domainname.md

pkg/specgen/generate/namespaces.go

docs/source/markdown/podman-create.1.md.in

cdoern · 2022-09-09T18:32:23Z

/hold

cdoern · 2022-10-11T17:17:02Z

@giuseppe @Luap99 @rhatdan PTAL, once my PR in runtime-tools gets merged in I think this is the proper structure.

cdoern · 2022-12-19T14:30:48Z

@giuseppe @rhatdan PTAL

docs/source/markdown/options/domainname.md

giuseppe · 2022-12-20T08:41:07Z

test/e2e/run_dns_test.go

@@ -99,6 +99,19 @@ var _ = Describe("Podman run dns", func() {
 		Expect(session.OutputToString()).To(ContainSubstring("foobar"))
 	})

+	It("podman run domainname sets /etc/hosts and /proc/sys/kernel/domainname", func() {
+		Skip("Waiting for crun release > 1.6")


crun 1.6 was released some time ago. Where is the test failing?

ah, let me un-comment that and see if this all works...

cdoern · 2022-12-20T18:07:33Z

@giuseppe it seems /proc/sys/kernel/domainname does not get set but /etc/hosts does. Does this mean the domainname is working or not? not sure if the /proc file is meant to be set

giuseppe · 2022-12-21T18:38:35Z

@giuseppe it seems /proc/sys/kernel/domainname does not get set but /etc/hosts does. Does this mean the domainname is working or not? not sure if the /proc file is meant to be set

it sounds like working from Podman but it doesn't look like working from the OCI runtime. To what test are you referring?

cdoern · 2022-12-21T20:00:07Z

@giuseppe it seems /proc/sys/kernel/domainname does not get set but /etc/hosts does. Does this mean the domainname is working or not? not sure if the /proc file is meant to be set

it sounds like working from Podman but it doesn't look like working from the OCI runtime. To what test are you referring?

@giuseppe I was checking /proc/sys/kernel/domainname in a test but I am not sure if that file is meant to contain the --domainname. running commands like hostname -A work appropriately though... so i am not sure if crun is doing it right or not.

rhatdan · 2022-12-21T20:46:47Z

# domainname dan
sh-5.2# domainname
dan
sh-5.2# cat /proc/sys/kernel/domainname 
dan

If I run a container I will also see domainname dan within it, which seems wrong, but I can change it

sh-5.2# podman run -ti --privileged fedora sh
# dnf -y install /usr/bin/domainname
...
Installed:
  hostname-3.23-7.fc37.x86_64                                                                                                                                                        

Complete!
# domainname
dan
# domainname walsh
# domainname
walsh
# exit
sh-5.2# domainname
dan

rhatdan · 2022-12-21T20:47:28Z

I would expect the /proc/sys/kernel/domainname to show the containers domainname, if this is set.

cdoern · 2022-12-22T02:11:33Z

I would expect the /proc/sys/kernel/domainname to show the containers domainname, if this is set.

ok, then I think this is an issue with crun. Since /etc/hosts seems to be updated and the spec does indeed have the proper domainname entity set, something must be wrong..

though, in crun all of the domainname tests pass. @giuseppe WDYT?

giuseppe · 2022-12-22T08:44:47Z

is the correct crun installed?

If I pull locally your changes (testing commit c91508b), I see it works:

$ sudo bin/podman run --rm --domainname as-root fedora cat /proc/sys/kernel/domainname
as-root
$ bin/podman run --rm --domainname and-also-rootless fedora cat /proc/sys/kernel/domainname
and-also-rootless

Instead of installing an additional package, let's change the test to print directly /proc/sys/kernel/domainname

cdoern · 2022-12-22T18:29:04Z

@giuseppe could ci have an old crun version?

giuseppe · 2022-12-22T18:48:12Z

yes I think that is the issue. It is using crun-1.6-2.fc36-x86_64 while the support was added in crun 1.7.

Let's not block on the CI, just skip the test for now

domainname functions similarly to --hostname, it sets the value in /etc/hosts to whatever you speficy in conjunction with --hostname. so if you pass --hostname=foo --domainmame=baz.net, /etc/hosts will get the combined entry and /proc/sys/kernel/domainname will get baz.net resolves containers#15102 Signed-off-by: Charlie Doern <cbddoern@gmail.com>

vrothberg · 2023-01-17T10:08:49Z

@cdoern I think rebasing and unskipping the test is possible now. Do you have time to tackle it?

Luap99 · 2023-01-17T13:25:32Z

@cdoern I think rebasing and unskipping the test is possible now. Do you have time to tackle it?

The VM image update is still blocked, so there were no updates since November so we are still on crun 1.6.2 at the moment AFAIK.

openshift-merge-robot · 2023-01-22T22:42:54Z

PR needs rebase.

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vrothberg · 2023-03-28T13:28:34Z

Friendly ping. @cdoern I think we are good to give it another try.

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defer creation of sysctl until after all namespaces have been created containers/crun#983

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add support for podman create/run --domainname #15200

add support for podman create/run --domainname #15200

cdoern commented Aug 4, 2022 •

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add support for podman create/run --domainname #15200

add support for podman create/run --domainname #15200

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cdoern commented Aug 4, 2022 • edited Loading

Does this PR introduce a user-facing change?

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