SecureContext
2023-03-10 本文已影响0人
程序员札记
简介
安全上下文（Security Context）定义 Pod 或 Container 的特权与访问控制设置。安全上下文包括但不限于：
- 自主访问控制（Discretionary Access Control）：基于 用户 ID（UID）和组 ID（GID）.来判定对对象（例如文件）的访问权限
- 安全性增强的 Linux（SELinux）：为对象赋予安全性标签。
- 以特权模式或者非特权模式运行。
- Linux 权能: 为进程赋予 root 用户的部分特权而非全部特权。
- AppArmor：使用程序文件来限制单个程序的权限。
- Seccomp：限制一个进程访问文件描述符的权限。
- AllowPrivilegeEscalation：控制进程是否可以获得超出其父进程的特权。此布尔值直接控制是否为容器进程设置no_new_privs 标志。当容器以特权模式运行或者具有 CAP_SYS_ADMIN权能时，- AllowPrivilegeEscalation 总是为 true。
- readOnlyRootFilesystem：以只读方式加载容器的根文件系统。
功能
2.1 配置pod的安全上下文
apiVersion: v1
kind: Pod
metadata:
name: security-context-demo
spec:
securityContext:
runAsUser: 1000
runAsGroup: 3000
fsGroup: 2000
volumes:
- name: sec-ctx-vol
emptyDir: {}
containers:
- name: sec-ctx-demo
image: busybox
command: [ "sh", "-c", "sleep 1h" ]
volumeMounts:
- name: sec-ctx-vol
mountPath: /data/demo
securityContext:
allowPrivilegeEscalation: false
- 在配置文件中，该runAsUser字段指定对于Pod中的任何容器，所有进程都以用户ID 1000运行。
- 该runAsGroup字段为Pod中的任何容器中的所有进程指定主组ID3000。如果省略此字段，则容器的主要组ID将为root（0）。runAsGroup指定时，用户1000和组3000也将拥有所有创建的文件。
- 由于fsGroup指定了字段，因此容器的所有进程也是补充组ID2000的一部分。卷的所有者/data/demo和在该卷中创建的任何文件都将是组ID 2000。
$ kubectl apply -f https://k8s.io/examples/pods/security/security-context.yaml
$ kubectl get pod security-context-demo
$ kubectl exec -it security-context-demo -- sh
$ ps
PID USER TIME COMMAND
1 1000 0:00 sleep 1h
6 1000 0:00 sh
...
$ cd /data
$ ls -l
drwxrwsrwx 2 root 2000 4096 Jun 6 20:08 demo
$ cd demo
$ echo hello > testfile
$ ls -l
-rw-r--r-- 1 1000 2000 6 Jun 6 20:08 testfile
$ id
uid=1000 gid=3000 groups=2000
2.2 为 Pod 配置卷访问权限和属主变更策略
况下，Kubernetes 在挂载一个卷时，会递归地更改每个卷中的内容的属主和访问权限，使之与 Pod 的 securityContext 中指定的 fsGroup 匹配。对于较大的数据卷，检查和变更属主与访问权限可能会花费很长时间，降低 Pod 启动速度。你可以在 securityContext 中使用 fsGroupChangePolicy 字段来控制 Kubernetes 检查和管理卷属主和访问权限的方式。
- fsGroupChangePolicy - fsGroupChangePolicy 定义在卷被暴露给 Pod 内部之前对其 内容的属主和访问许可进行变更的行为。此字段仅适用于那些支持使用 fsGroup 来 控制属主与访问权限的卷类型。此字段的取值可以是：
-OnRootMismatch：只有根目录的属主与访问权限与卷所期望的权限不一致时，才改变其中内容的属主和访问权限。这一设置有助于缩短更改卷的属主与访问权限所需要的时间。
Always：在挂载卷时总是更改卷中内容的属主和访问权限。
securityContext:
runAsUser: 1000
runAsGroup: 3000
fsGroup: 2000
fsGroupChangePolicy: "OnRootMismatch"
这是一个Alpha功能。要使用它，请为kube-api-server，kube-controller-manager和kubelet 启用功能门 ConfigurableFSGroupPolicy。
2.3 对启动的容器使用sysctl修改内核参数，比如es这类容器镜像。
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: sc-demo
spec:
template:
containers:
- name: sc-demo
image: xxxxxx
command: [ "sh", "-c", "sleep 1h" ]
securityContext:
privileged: true
给予 privileged: true 是一个比较粗的权限，一般不建议如此，可以为权限定义更细粒度的权限，类似需要在容器中使用 perf 命令，则可以进行如下定义：
...
securityContext:
capabilities:
add: ["SYS_ADMIN"]
具体 capabilities 的使用规则可参考：在 Kubernetes 中配置 Container Capabilities
2.4 对启动的容器赋予SELinux标签
...
securityContext:
seLinuxOptions:
level: "s0:c123,c456"
要指定 SELinux，需要在宿主操作系统中装载 SELinux 安全性模块。seLinuxOptions 字段的取值是一个 SELinuxOptions 对象
- 实例
image.png
参考链接：
https://kubernetes.io/docs/tasks/configure-pod-container/security-context/#before-you-begin
3.1 Set Container User and Group
root@master:~/cks/securitytext# k run pod --image=busybox --command -oyaml --dry-run=client > pod.yaml -- sh -c 'sleep 1d'
root@master:~/cks/securitytext# cat pod.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: pod
name: pod
spec:
securityContext:
runAsUser: 1000
runAsGroup: 3000
containers:
- command:
- sh
- -c
- sleep 1d
image: busybox
name: pod
resources: {}
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
root@master:~/cks/securitytext# k create -f pod.yaml
root@master:~/cks/security# k get pods
NAME READY STATUS RESTARTS AGE
pod 1/1 Running 0 83s
root@master:~/cks/securitytext# k exec -ti pod -- sh
/ $ id
uid=1000 gid=3000
/ $ touch test
touch: test: Permission denied
/ $ cd /tmp
/tmp $ touch test
/tmp $ ls -lh
total 0
-rw-r--r-- 1 1000 3000 0 May 15 15:00 test
`
3.2 Force Container Non-Root
root@master:~/cks/securitytext# vim pod.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: pod
name: pod
spec:
securityContext:
runAsUser: 1000
runAsGroup: 3000
containers:
- command:
- sh
- -c
- sleep 1d
image: busybox
name: pod
resources: {}
securityContext:
runAsNonRoot: true
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
root@master:~/cks/securitytext# kubectl -f pod.yaml delete --force --grace-period=0
warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
pod "pod" force deleted
root@master:~/cks/securitytext# k create -f pod.yaml
pod/pod created
root@master:~/cks/securitytext# k get pod
NAME READY STATUS RESTARTS AGE
pod 1/1 Running 0 68s
#未指定非root用户
root@master:~/cks/securitytext# vim pod.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: pod
name: pod
spec:
# securityContext:
# runAsUser: 1000
# runAsGroup: 3000
containers:
- command:
- sh
- -c
- sleep 1d
image: busybox
name: pod
resources: {}
securityContext:
runAsNonRoot: true
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
root@master:~/cks/securitytext# kubectl -f pod.yaml delete --force --grace-period=0
warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
pod "pod" force deleted
root@master:~/cks/securitytext# k create -f pod.yaml
pod/pod created
oot@master:~/cks/securitytext# k get pod
NAME READY STATUS RESTARTS AGE
pod 0/1 CreateContainerConfigError 0 22s
#报错
root@master:~/cks/securitytext# k describe pod pod
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 50s default-scheduler Successfully assigned default/pod to node2
Normal Pulled 33s kubelet Successfully pulled image "busybox" in 16.355541429s
Warning Failed 29s (x2 over 33s) kubelet Error: container has runAsNonRoot and image will run as root (pod: "pod_default(99f9dcab-cebe-4432-ad70-08c86d3ed9be)", container: pod)
Normal Pulled 29s kubelet Successfully pulled image "busybox" in 2.345508306s
Normal Pulling 16s (x3 over 49s) kubelet Pulling image "busybox"
3.3 Privileged Containers
image.png
image.png
3.4 Create Privileged Containers
image.png
#非root用户测试执行sysctl命令
root@master:~/cks/securitytext# k get pods -w
NAME READY STATUS RESTARTS AGE
pod 0/1 ContainerCreating 0 3s
pod 1/1 Running 0 23s
root@master:~/cks/securitytext# k exec -ti pod -- sh
/ $ sysctl kernel.hostname=attacker
sysctl: error setting key 'kernel.hostname': Read-only file system #无权限
/ $ exit
command terminated with exit code 1
#默认用户测试执行sysctl命令
root@master:~/cks/securitytext# vim pod.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: pod
name: pod
spec:
# securityContext:
# runAsUser: 1000
# runAsGroup: 3000
containers:
- command:
- sh
- -c
- sleep 1d
image: busybox
name: pod
resources: {}
# securityContext:
# runAsNonRoot: true
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
root@master:~/cks/securitytext# kubectl -f pod.yaml delete --force --grace-period=0
warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
pod "pod" force deleted
root@master:~/cks/securitytext# k create -f pod.yaml
pod/pod created
root@master:~/cks/securitytext# k get pods
NAME READY STATUS RESTARTS AGE
pod 1/1 Running 0 32s
root@master:~/cks/securitytext# k exec -ti pod -- sh
/ # sysctl kernel.hostname=attacker
sysctl: error setting key 'kernel.hostname': Read-only file system #无权限
/ # id
uid=0(root) gid=0(root) groups=10(wheel)
#添加privileged: true特权
root@master:~/cks/securitytext# vim pod.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: pod
name: pod
spec:
# securityContext:
# runAsUser: 1000
# runAsGroup: 3000
containers:
- command:
- sh
- -c
- sleep 1d
image: busybox
name: pod
resources: {}
securityContext:
privileged: true
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
root@master:~/cks/securitytext# kubectl -f pod.yaml delete --force --grace-period=0
warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
pod "pod" force deleted
root@master:~/cks/securitytext# k create -f pod.yaml
pod/pod created
root@master:~/cks/securitytext# k get pod
NAME READY STATUS RESTARTS AGE
pod 1/1 Running 0 36s
root@master:~/cks/securitytext# k exec -ti pod -- sh
/ # id
uid=0(root) gid=0(root) groups=10(wheel)
/ # sysctl kernel.hostname=attacker #命令生效
kernel.hostname = attacker
3.5 PrivilegeEscalation
image.png
image.png
3.6 Practice - Disable PriviledgeEscalation
image.png
root@master:~/cks/securitytext# vim pod.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: pod
name: pod
spec:
# securityContext:
# runAsUser: 1000
# runAsGroup: 3000
containers:
- command:
- sh
- -c
- sleep 1d
image: busybox
name: pod
resources: {}
securityContext:
allowPrivilegeEscalation: true
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
root@master:~/cks/securitytext# kubectl -f pod.yaml delete --force --grace-period=0
warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
pod "pod" force deleted
root@master:~/cks/securitytext# k create -f pod.yaml
pod/pod created
root@master:~/cks/securitytext# k get pod
NAME READY STATUS RESTARTS AGE
pod 1/1 Running 0 29s
root@master:~/cks/securitytext# k exec -ti pod -- sh
/ # cat /proc/1/status
Name: sleep
State: S (sleeping)
Tgid: 1
Ngid: 0
Pid: 1
PPid: 0
TracerPid: 0
Uid: 0 0 0 0
Gid: 0 0 0 0
FDSize: 64
Groups: 10
NStgid: 1
NSpid: 1
NSpgid: 1
NSsid: 1
VmPeak: 1308 kB
VmSize: 1308 kB
VmLck: 0 kB
VmPin: 0 kB
VmHWM: 4 kB
VmRSS: 4 kB
VmData: 48 kB
VmStk: 132 kB
VmExe: 892 kB
VmLib: 18446744073709551612 kB
VmPTE: 12 kB
VmPMD: 8 kB
VmSwap: 0 kB
HugetlbPages: 0 kB
Threads: 1
SigQ: 0/7778
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000004
SigCgt: 0000000000000000
CapInh: 00000000a80425fb
CapPrm: 00000000a80425fb
CapEff: 00000000a80425fb
CapBnd: 00000000a80425fb
CapAmb: 0000000000000000
Seccomp: 0
Speculation_Store_Bypass: thread vulnerable
Cpus_allowed: 00000000,00000000,00000000,00000003
Cpus_allowed_list: 0-1
Mems_allowed: 00000000,00000001
Mems_allowed_list: 0
voluntary_ctxt_switches: 47
nonvoluntary_ctxt_switches: 10
