libct/cap: switch to moby/sys/capability, lazy init #4358

kolyshkin · 2024-07-23T00:28:37Z

This has started as a simple way to reduce init() overhead in libcontainer/capabilities, but ended up switching to the fork of gocapability package, and also fixing a big issue in handling of ambient capabilities.

Please see individual commits for details; I will open an issue about ambient caps tomorrow.

libcontainer/capabilities/capabilities.go

thaJeztah

LGTM; left one suggestion (not blocking)

rata

LGTM, thanks!

rata · 2024-07-30T09:00:34Z

This still LGTM. Let me know if it's ready, IMHO this is ready to merge.

thaJeztah · 2024-08-01T06:41:23Z

@kolyshkin was the last commit intended for this PR, or for a follow up?

go.mod

kolyshkin · 2024-08-01T09:05:52Z

@kolyshkin was the last commit intended for this PR, or for a follow up?

I can split this PR into two, but really I want all this to be merged (and you don't have to re-review the first two commits).

kolyshkin · 2024-08-02T05:34:55Z

we want mv github.com/kolyshkin/capability to github.com/opencontainers/capability can you help me move [https://github.com/kolyshkin/capability] to under opencontainers org? @gregkh @bfirsh

Please don't tag people you don't know. These are definitely not those who can help. We will figure it out.

rata

This mostly LGTM, left some comments

libcontainer/capabilities/capabilities.go

rata · 2024-08-02T10:08:21Z

libcontainer/capabilities/capabilities.go

 				out = append(out, v)
 			}
 		}
 		return out
 	}
+	inheritable := capSlice(capConfig.Inheritable, nil)
+	// Ambient vector can not contain values not raised in the Inheritable vector,


The whole sentence from: https://pkg.go.dev/kernel.org/pub/linux/libs/security/libcap/cap#section-readme is:

Note, the Ambient vector cannot contain values not raised in the Inh vector, so setting values directly in one vector may have the side effect of mirroring the value in the other vector to maintain this constraint

I guess we want to ignore it, instead of adding it, as we are doing for a long time now. But wanted to raise this, just in case.

Yes, that library raises inheritable bits where the corresponding ambient bits are raised.

I agree that we should not change the behavior (and instead maybe document that if you want to raise ambient caps, you have to raise inheritable ones as well).

kolyshkin · 2024-09-26T05:42:07Z

No longer a draft; PTAL @lifubang @AkihiroSuda @thaJeztah

lifubang · 2024-09-27T15:37:36Z

libcontainer/capabilities/capabilities.go

+	// compatibility we have to ignore those Ambient caps that are not also raised
+	// in Inheritable (and issue a warning).
+	ambient := capSlice(capConfig.Ambient, inheritable)
+	if len(ignoredCaps) > 0 {


There are at least 2 conditions to return error when setting ambient caps:

The ambient cap sets is not in both permitted and inheritable cap sets;

The PR_CAP_AMBIENT_LOWER securebit has been set.

So maybe this is not enough. I take another easy way to implement this compatibility. (#4418)

This PR handles condition 1. As for condition 2, it works as it used to work before, no changes needed here.

In general, I think, we should return an error when we're unable to set a capability requested. The warning which this PR adds is a temporary measure, to ensure we're not breaking our users. Eventually this warning should become an error.

This PR handles condition 1.

Because of ‘both permitted and inheritable cap sets’.

Even in condition 1, I think you need to add check ‘permitted’ too, not only ‘inheritable’. Please see my first commit in #4418 .

As for condition 2, it works as it used to work before, no changes needed here.

I think this error was also masked before this PR, but will be failed in the future. It should have a compatibility like condition 1.

Even in condition 1, I think you need to add check ‘permitted’ too, not only ‘inheritable’. Please see my first commit in #4418 .

It looks like such configuration is not working in the current runc version:

@test "runc run [raise inheritable bit not set in permitted]" { update_config ' .process.capabilities.inheritable = ["CAP_KILL"] | .process.capabilities.permitted = ["CAP_CHOWN"]' # | .process.capabilities.ambient = ["CAP_KILL", "CAP_CHOWN"]' runc run testct [ "$status" -eq 0 ]

runc run testct (status=1): time="2024-09-27T17:31:28-07:00" level=error msg="runc run failed: unable to start container process: error during container init: unable to apply caps: operation not permitted"

This means:

If it's not working now, it should not start work in the future.

We don't have to check for permitted bit set when checking ambient.

As for condition 2, it works as it used to work before, no changes needed here.

I think this error was also masked before this PR, but will be failed in the future. It should have a compatibility like condition 1.

You might be right, I need to check it.

It looks like such configuration is not working in the current runc version:

31be074

kolyshkin · 2024-09-27T21:21:25Z

@cyphar @AkihiroSuda PTAL

lifubang · 2024-10-08T02:24:31Z

@AkihiroSuda There is at least one error in this PR(#4358 (comment)), I suggest to wait moby/sys/capability to make an new release(moby/sys#165).

rata · 2024-10-09T11:11:00Z

@lifubang Thanks, but can you elaborate on what is the error exactly? The link to a test case, what does that mean? Should that test fail? Or is it working and it shouldn't? Is that before/after the PR? What do you want to show exactly? I'll check-out this branch and test myself, but it would be great if you can elaborate more on your concern.

lifubang · 2024-10-09T12:40:27Z

but can you elaborate on what is the error exactly?

#4358 (comment)
This PR will cause at least these two regressions.

The link to a test case, what does that mean?

It means the regression 1. So, how about merge this test case first to ensure we can't introduce any regression in the future?

lifubang · 2024-10-09T12:54:23Z

I think we can split this PR to 3 PRs, then we can push the progress more easily.
PR 1: Switch to github.com/moby/sys/capability, this PR should not change any ~~logic~~behavior of runc, because we should replace the dependency package which has a long time bug and is in a unmaintained state ASAP;
PR 2: libct/cap: switch to lazy init;
PR 3: Improve the error msgs of cap set.

But unfortunately, there are still some bugs in github.com/moby/sys/capability. So we need to wait a new release of it.

rata · 2024-10-09T13:04:17Z

@lifubang I fully agree, let's make this PR be 1 or 1 and 2. And PR 3 can be done later, maybe even after the 1.2.0 release (I'm not sure I'd hold the release for adding a warning, especially something that has been like this for a long time).

@kolyshkin what do you think?

kolyshkin · 2024-10-12T19:30:21Z

PR 1: Switch to github.com/moby/sys/capability, this PR should not change any ~~logic~~behavior of runc, because we should replace the dependency package which has a long time bug and is in a unmaintained state ASAP;

Unfortunately it does change the behavior, because of the bug in the original package which is fixed in the fork (kolyshkin/capability#3).

Even if we try to work around this (set the AMBIENT caps separately and ignore the error), it will still change the behavior, because the fork returns the error as soon as it has it, while the original package keep going and tries to set all capabilities.

To solve this, we need something like AmbientRaise which is being added by moby/sys#165. As soon as it is merged and a new release is made, we can make the "PR 1 " work with maximum level of compatibility with the current version.

kolyshkin · 2024-10-12T19:33:23Z

But unfortunately, there are still some bugs in github.com/moby/sys/capability. So we need to wait a new release of it.

More like "missing functionality" (of setting ambient capabilities one by one), although we can actually use x/sys/unix for that.

The only bug I'm aware of is this one, and it does not affect runc in any way.

lifubang · 2024-10-15T13:22:11Z

To solve this, we need something like AmbientRaise which is being added by moby/sys#165. As soon as it is merged and a new release is made, we can make the "PR 1 " work with maximum level of compatibility with the current version.

Yes, like #4418, it is the final usage after we release moby/sys/capability v0.4.0.

Signed-off-by: Kir Kolyshkin <[email protected]>

A map which is created in func init is only used by capSlice, which is only used by New, which is only used by runc init. Switch to lazy init to slightly save on startup time. Signed-off-by: Kir Kolyshkin <[email protected]>

This removes the last unversioned package in runc's direct dependencies. Signed-off-by: Kir Kolyshkin <[email protected]>

kolyshkin · 2024-11-12T07:53:39Z

moby/sys/capability v0.4.0 released; this PR is rebased and (hopefully) ready for review.

PTAL @thaJeztah @lifubang

kolyshkin mentioned this pull request Jul 23, 2024

runc aways open "/proc/sys/kernel/cap_last_cap" #4356

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kolyshkin marked this pull request as ready for review July 23, 2024 17:45

thaJeztah reviewed Jul 23, 2024

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kolyshkin force-pushed the rm-cap-init branch from 351ab7e to 2bb6167 Compare July 29, 2024 20:37

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kolyshkin changed the title ~~libct/cap: switch to lazy init~~ libct/cap: switch to kolyshkin/capability, lazy init, fix for ambient caps Aug 1, 2024

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This was referenced Aug 6, 2024

DRAFT:replace github.com/syndtr/gocapability with github.com/kolyshkin/capa… #4362

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Move this repo to an org kolyshkin/capability#14

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kolyshkin changed the title ~~libct/cap: switch to kolyshkin/capability, lazy init, fix for ambient caps~~ libct/cap: switch to kolyshkin/capability, lazy init Aug 6, 2024

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Add capability package moby/sys#149

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kolyshkin changed the title ~~libct/cap: switch to kolyshkin/capability, lazy init~~ libct/cap: switch to moby/sys/capability, lazy init Sep 12, 2024

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libct/cap: switch to moby/sys/capability #4418

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cyphar mentioned this pull request Oct 2, 2024

Blockers for v1.2.0 #4114

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kolyshkin mentioned this pull request Oct 4, 2024

Treating unknown/unavailable capabilities #4426

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kolyshkin added 3 commits November 11, 2024 23:48

libct/cap: preallocate slices

e9f3562

Signed-off-by: Kir Kolyshkin <[email protected]>

libct/cap: switch to lazy init

2065557

A map which is created in func init is only used by capSlice, which is only used by New, which is only used by runc init. Switch to lazy init to slightly save on startup time. Signed-off-by: Kir Kolyshkin <[email protected]>

Switch to github.com/moby/sys/capability v0.4.0

fc9a0a6

This removes the last unversioned package in runc's direct dependencies. Signed-off-by: Kir Kolyshkin <[email protected]>

kolyshkin force-pushed the rm-cap-init branch from 490ab7a to fc9a0a6 Compare November 12, 2024 07:53

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libct/cap: switch to moby/sys/capability, lazy init #4358

libct/cap: switch to moby/sys/capability, lazy init #4358

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libct/cap: switch to moby/sys/capability, lazy init #4358

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