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linux: reject sysctl kernel.domainname when OCI knob domainname is set #1017

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merged 1 commit into from
Oct 4, 2022

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flouthoc
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@flouthoc flouthoc commented Oct 1, 2022

Setting sysctl kernel.domainname directly by user is not environment agnostic, it shows either incorrect ( on non-working ) behaviour in rootless environment.

It was decided to make this part of runtime-spec so the OCI runtime can itself handle this behaviour correctly. As a result a new field domainname was added to runtime-spec. Since crun already implementes this field therefore sysctl configured by user conflicts with the behaviour expected by the OCI runtime.

Runtime-spec PR: opencontainers/runtime-spec#1156

Furthermore a similar sysctl kernal.hostname is blocked by crun explicitly to prevent this conflicting behaviour. https://github.com/containers/crun/blob/main/src/libcrun/linux.c#L3203

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flouthoc commented Oct 1, 2022

Previous discussion here: opencontainers/runtime-spec#1156 (comment)

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flouthoc commented Oct 1, 2022

@giuseppe @AkihiroSuda PTAL, I think we should block kernel.domainname but I think then runc would also need this change so that there is parity.

@flouthoc flouthoc marked this pull request as draft October 1, 2022 11:47
@flouthoc flouthoc marked this pull request as ready for review October 1, 2022 12:18
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rhatdan commented Oct 1, 2022

@kolyshkin WDYT?

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AkihiroSuda commented Oct 1, 2022

It is still a valid sysctl value and not rejected in the Runtime spec, so no need to reject it in crun/runc IMHO

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flouthoc commented Oct 1, 2022

@AkihiroSuda Ah while writing/running tests it looked like, kernel.domainname has a conflicting nature with the new field domainname. I did a quick check in runc code I think other sysctls are blocked because of same reason ( See: https://github.com/opencontainers/runc/blob/main/libcontainer/configs/validate/validator.go#L207 )

But if we decide to allow this, should we specify which one will take priority is it sysctl or the field domainname ?

Edit: there is also this line in validator https://github.com/opencontainers/runc/blob/main/libcontainer/configs/validate/validator.go#L203

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giuseppe commented Oct 2, 2022

I think we should reject the sysctl only when the domainname value is also set.

Otherwise, we risk breaking older users that were using the sysctl directly.

@flouthoc flouthoc force-pushed the reject-sysctl-domainname branch from 6894b64 to fc46676 Compare October 3, 2022 02:27
@flouthoc flouthoc changed the title linux: reject sysctl kernel.domainname in favor of OCI knob domainname linux: reject sysctl kernel.domainname when OCI knob domainname is set Oct 3, 2022
@flouthoc flouthoc force-pushed the reject-sysctl-domainname branch from fc46676 to ab895b8 Compare October 3, 2022 02:30
// conflict with already set field `domainname` in
// OCI spec, in such scenario crun will fail to prevent
// unexpected behaviour for end user.
return crun_make_error (err, 0, "the sysctl `%s` conflicts with OCI field `domainname`", original_value);

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Probably no need to raise an error if strcmp(name, def->domainname) == 0

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@AkihiroSuda I think you meant strcmp(original_value, def->domainname) , since name is the key of sysctl which is kernel.domainname.

I have added this condition and also a test for this.

@flouthoc flouthoc force-pushed the reject-sysctl-domainname branch 2 times, most recently from ee34c11 to 2c73b88 Compare October 3, 2022 03:17
Setting sysctl `kernel.domainname` directly by user is not environment
agnostic, it shows either incorrect ( on non-working ) behaviour in
`rootless` environment.

It was decided to make this part of `runtime-spec` so the OCI runtime
can itself handle this behaviour correctly. As a result a new field
`domainname` was added to `runtime-spec`. Since crun already implementes
this field therefore `sysctl` configured by user conflicts with the
behaviour expected by the OCI runtime.

Runtime-spec PR: opencontainers/runtime-spec#1156

Furthermore a similar `sysctl` `kernal.hostname` is blocked by crun explicitly
to prevent this conflicting behaviour. https://github.com/containers/crun/blob/main/src/libcrun/linux.c#L3203

Following commit ensures that crun rejects sysctl `kernel.domainname`
when OCI field `domainname` is already set.

Signed-off-by: Aditya R <arajan@redhat.com>
@flouthoc flouthoc force-pushed the reject-sysctl-domainname branch from 2c73b88 to 391df45 Compare October 3, 2022 03:21
@flouthoc flouthoc requested review from AkihiroSuda and giuseppe and removed request for AkihiroSuda October 3, 2022 03:30
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LGTM

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Runc issue for similar PR: opencontainers/runc#3629

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4 participants