Linux Capabilities

External

• https://man7.org/linux/man-pages/man7/capabilities.7.html
• https://linux-audit.com/linux-capabilities-hardening-linux-binaries-by-removing-setuid/
• https://docs.docker.com/engine/security/security/#linux-kernel-capabilities
• https://github.com/torvalds/linux/blob/master/include/uapi/linux/capability.h

Internal

• Linux Security
• Linux Security Concepts
• Kubernetes Pod and Container Security

Overview

Traditional UNIX implementations distinguish two categories of processes for the purpose of performing permission checks: privileged processes and unprivileged processes. A privileged process is a process with its effective user ID is 0, referred to as superuser or root. An unprivileged process is a process with a non-zero its effective user ID. Privileged processes bypass all kernel permission checks, while unprivileged processes are subject to full permission checking based on the process' credentials: effective UID, effective GID and supplementary group list.

Starting with kernel 2.2, Linux divides the privileges traditionally associated with superuser into distinct units, known as Linux (or kernel) capabilities, which can be independently enabled and disabled. Instead of making a process privileged and giving it unlimited permissions, a much safer method from a security perspective is to give it access only to the kernel features it really requires. Capabilities are a per-thread attribute.

Display Capabilities for a Process

Get the PID and then:

cd /proc/<pid>
cat status

...
CapInh:	00000000a80425fb
CapPrm:	00000000a80425fb
CapEff:	00000000a80425fb
CapBnd:	00000000a80425fb
CapAmb:	0000000000000000
...

Common Capabilities

CAP_SYS_TIME

Bit 25.

CAP_SYS_ADMIN

Allows a range of administrative operations.

CAP_SYS_MODULE

Allows loading and unloading of Linux kernel modules.

CAP_NET_ADMIN

Bit 12.