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更多关于kubernetes的深入文章，请看我csdn或者oschina的博客主页。
Docker Container Capabilities
在docker run命令中，我们可以通过--cap-add和--cap-drop来给容器添加linux Capabilities。下面表格中的列出的Capabilities是docker默认给容器添加的，用户可以通过--cap-drop去除其中一个或者多个。
| Docker’s capabilities | Linux capabilities | Capability Description |
|---|---|---|
| SETPCAP | CAP_SETPCAP | Modify process capabilities. |
| MKNOD | CAP_MKNOD | Create special files using mknod(2). |
| AUDIT_WRITE | CAP_AUDIT_WRITE | Write records to kernel auditing log. |
| CHOWN | CAP_CHOWN | Make arbitrary changes to file UIDs and GIDs (see chown(2)). |
| NET_RAW | CAP_NET_RAW | Use RAW and PACKET sockets. |
| DAC_OVERRIDE | CAP_DAC_OVERRIDE | Bypass file read, write, and execute permission checks. |
| FOWNER | CAP_FOWNER | Bypass permission checks on operations that normally require the file system UID of the process to match the UID of the file. |
| FSETID | CAP_FSETID | Don’t clear set-user-ID and set-group-ID permission bits when a file is modified. |
| KILL | CAP_KILL | Bypass permission checks for sending signals. |
| SETGID | CAP_SETGID | Make arbitrary manipulations of process GIDs and supplementary GID list. |
| SETUID | CAP_SETUID | Make arbitrary manipulations of process UIDs. |
| NET_BIND_SERVICE | CAP_NET_BIND_SERVICE | Bind a socket to internet domain privileged ports (port numbers less than 1024). |
| SYS_CHROOT | CAP_SYS_CHROOT | Use chroot(2), change root directory. |
| SETFCAP | CAP_SETFCAP | Set file capabilities. |
下面表格中列出的Capabilities是docker默认删除的Capabilities，用户可以通过--cap-add添加其中一个或者多个。
| Docker’s capabilities | Linux capabilities | Capability Description |
|---|---|---|
| SYS_MODULE | CAP_SYS_MODULE | Load and unload kernel modules. |
| SYS_RAWIO | CAP_SYS_RAWIO | Perform I/O port operations (iopl(2) and ioperm(2)). |
| SYS_PACCT | CAP_SYS_PACCT | Use acct(2), switch process accounting on or off. |
| SYS_ADMIN | CAP_SYS_ADMIN | Perform a range of system administration operations. |
| SYS_NICE | CAP_SYS_NICE | Raise process nice value (nice(2), setpriority(2)) and change the nice value for arbitrary processes. |
| SYS_RESOURCE | CAP_SYS_RESOURCE | Override resource Limits. |
| SYS_TIME | CAP_SYS_TIME | Set system clock (settimeofday(2), stime(2), adjtimex(2)); set real-time (hardware) clock. |
| SYS_TTY_CONFIG | CAP_SYS_TTY_CONFIG | Use vhangup(2); employ various privileged ioctl(2) operations on virtual terminals. |
| AUDIT_CONTROL | CAP_AUDIT_CONTROL | Enable and disable kernel auditing; change auditing filter rules; retrieve auditing status and filtering rules. |
| MAC_OVERRIDE | CAP_MAC_OVERRIDE | Allow MAC configuration or state changes. Implemented for the Smack LSM. |
| MAC_ADMIN | CAP_MAC_ADMIN | Override Mandatory Access Control (MAC). Implemented for the Smack Linux Security Module (LSM). |
| NET_ADMIN | CAP_NET_ADMIN | Perform various network-related operations. |
| SYSLOG | CAP_SYSLOG | Perform privileged syslog(2) operations. |
| DAC_READ_SEARCH | CAP_DAC_READ_SEARCH | Bypass file read permission checks and directory read and execute permission checks. |
| LINUX_IMMUTABLE | CAP_LINUX_IMMUTABLE | Set the FS_APPEND_FL and FS_IMMUTABLE_FL i-node flags. |
| NET_BROADCAST | CAP_NET_BROADCAST | Make socket broadcasts, and listen to multicasts. |
| IPC_LOCK | CAP_IPC_LOCK | Lock memory (mlock(2), mlockall(2), mmap(2), shmctl(2)). |
| IPC_OWNER | CAP_IPC_OWNER | Bypass permission checks for operations on System V IPC objects. |
| SYS_PTRACE | CAP_SYS_PTRACE | Trace arbitrary processes using ptrace(2). |
| SYS_BOOT | CAP_SYS_BOOT | Use reboot(2) and kexec_load(2), reboot and load a new kernel for later execution. |
| LEASE | CAP_LEASE | Establish leases on arbitrary files (see fcntl(2)). |
| WAKE_ALARM | CAP_WAKE_ALARM | Trigger something that will wake up the system. |
| BLOCK_SUSPEND | CAP_BLOCK_SUSPEND | Employ features that can block system suspend. |
比如，我们可以通过给给容器add NET_ADMIN Capability，使得我们可以对network interface进行modify，对应的docker run命令如下：
$ docker run -it --rm --cap-add=NET_ADMIN ubuntu:14.04 ip link add dummy0 type dummy
Kubernetes SecurityContext
在Kubernetes对Pod的定义中，用户可以add/drop Capabilities在Pod.spec.containers.sercurityContext.capabilities中添加要add的Capabilities list和drop的Capabilities list。
比如，我要添加NET_ADMIN Capability，删除KILL Capability，则对应的Pod定义如下：
apiVersion: v1
kind: Pod
metadata:
name: hello-world
spec:
containers:
- name: friendly-container
image: "alpine:3.4"
command: ["/bin/echo", "hello", "world"]
securityContext:
capabilities:
add:
- NET_ADMIN
drop:
- KILL
总结
Kubernetes通过在Pod.spec.containers.sercurityContext.capabilities中配置容器待add和drop的Capabilities，最终借助docker container Capabilities的能力，完成容器的Capabilities权限控制。
更多关于kubernetes的深入文章，请看我csdn或者oschina的博客主页。