Enable SECCOMP_FILTER_FLAG_SPEC_ALLOW per default
#938
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It’s a breaking change for runc :( |
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is this still a breaking change for runc or can we merge it? |
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: giuseppe, rhatdan, saschagrunert The full list of commands accepted by this bot can be found here. The pull request process is described here
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Let's wait for opencontainers/runc#3390 to be merged first. Then we need a new runc release. |
| // SECCOMP_RET_ALLOW should be logged. An administrator may override this | ||
| // filter flag by preventing specific actions from being logged via the | ||
| // /proc/sys/kernel/seccomp/actions_logged file. (since Linux 4.14) | ||
| SeccompFilterFlagLog = "SECCOMP_FILTER_FLAG_LOG" |
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is there a risk that a malicious container could fill the log if this is enabled by default?
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The log message always has a limited line length accordingly to: https://github.com/torvalds/linux/blob/23d04328444a8fa0ca060c5e532220dac8e8bc26/kernel/auditsc.c#L2946-L2970
The kernel has an audit rate limit as well as backlog limit. Auditd has a file rotation in place as well.
In theory users can still specify SCMP_ACT_LOG as default action, which would log all syscalls and not exclude the allowed ones.
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The log filter level may have a negative performance impact, I'll do some testing around this.
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Benchmark results
Environment
- Linux 5.16.10
- cri-o 1.23.1
- Kubernetes 1.23.4
Test pod
apiVersion: v1
kind: Pod
metadata:
name: test-pod
spec:
containers:
- name: test-container
securityContext:
seccompProfile:
type: RuntimeDefault
image: nginx:1.21.6Test
ab -n 100000 -c 100 http://$HOST/index.html
Results
| Seccomp Profile | Test time (in sec) | Requests per second |
|---|---|---|
| RuntimeDefault | 5.0 | 19913.1 |
RuntimeDefault (modified to log sendfile 1x per request) |
46.3 | 2156.4 |
RuntimeDefault (modified to log close 2x per request) |
93.6 | 1068.7 |
{ "defaultAction": "SCMP_ACT_LOG" } |
521.9 | 191.5 |
| Unconfined | 5.1 | 19323.4 |
It's interesting to see the impact of logging, which is executed in the kernel there:
https://github.com/torvalds/linux/blob/7e57714cd0ad2d5bb90e50b5096a0e671dec1ef3/kernel/auditsc.c#L2946-L2970
My local machine spikes audit CPU usage during the test, for example with SCMP_ACT_LOG:
Audit settings:
> sudo auditctl -s
enabled 1
failure 1
pid 803
rate_limit 0
backlog_limit 64
lost 163
backlog 65
backlog_wait_time 60000
loginuid_immutable 0 unlocked
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Just curious: why enable |
It's boosting performance, see: http://mamememo.blogspot.com/2020/05/cpu-intensive-rubypython-code-runs.html |
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SECCOMP_FILTER_FLAG_LOG and SECCOMP_FILTER_FLAG_SPEC_ALLOW per defaultSECCOMP_FILTER_FLAG_SPEC_ALLOW per default
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We now enable the flag for the default seccomp profile. Signed-off-by: Sascha Grunert <[email protected]>
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@saschagrunert cool. And being vulnerable by default is not a problem, I guess? |
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If we add this, should we make it more optional, so users could easily turn it on and off? One issue I have with SECCOMP is that it is almost impossible for normal users to customize. If this is a security versus performance change, is there a way we could add a flag to --security-opt seccomp:SPEC_ALLOW ... |
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Hm, it may be better than to leave it as it is for RuntimeDefault. crun is using it as a default as well: I also found some referring discussions in moby/moby#41389 and opencontainers/runc#2430. |
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@saschagrunert thanks! |
We now enable the flag for the default seccomp profile.
/hold