nscaps

Documentation

Overview

nscaps determines a process' capabilities in some namespace. It shows the process and namespace in their user namespace hierarchy or hierarchies, together with the process' own effective capabilities as well as the capabilities set gained in the specified namespace. Additionally, nscaps shows indications whether user namespaces along the hierarchy would be accessible or inaccessible to the specified process.

The nscaps tool has been inspired by Michael Kerrisk's gem http://man7.org/tlpi/code/online/dist/namespaces/ns_capable.c, but is an independent implementation and comes with wacky tree output, including funny unicode adornments.

Usage

To use nscaps:

nscaps [flag] NAMESPACE

For example, to view the capabilities of the current shell in your current network namespace (which are usually none as an ordinary user):

nscaps $(readlink /proc/$$/ns/net)

Compare this with what root will get:

sudo nscaps $(readlink /proc/$$/ns/net)

Flags

The following nscaps flags are available:

    --brief                  show only a summary statement for the capabilities in the target namespace
-c, --color color[=always]   colorize the output; can be 'always' (default if omitted), 'auto',
                             or 'never' (default auto)
    --dump                   dump colorization theme to stdout (for saving to ~/.lxknsrc.yaml)
-h, --help                   help for nscaps
    --icon                   show/hide unicode icons next to namespaces
-n, --ns string              PID namespace of PID, if not the initial PID namespace;
                             either an unsigned int64 value, such as "4026531836", or a
                             PID namespace textual representation like "pid:[4026531836]"
-p, --pid uint32             PID of process for which to calculate capabilities
    --proc proc[=name]       process name style; can be 'name' (default if omitted), 'basename',
                             or 'exe' (default name)
    --proccaps               show the process' capabilities (default true)
    --theme theme            colorization theme 'dark' or 'light' (default dark)
    --treestyle treestyle    select the tree render style; can be 'line' (default if omitted)
                             or 'ascii' (default line)
-v, --version                version for nscaps

Display

nscaps shows a tree containing only one or at most two branches: one containing the specified process (defaults to the nscaps process), and a second containing the specified namespace. A simple "nscaps $(readlink /proc/$$/ns/net)" as a non-root user will show the following output (subject to different namespace IDs):

⛛ user:[4026531837] process "systemd" (129419)
├─ process "nscaps" (208439)
│     ⋄─ (no capabilities)
└─ target net:[4026531905] process "systemd" (129419)
      ⋄─ (no effective capabilities)

Our (discovery) process has no effective capabilities, and so we don't get any capabilities on our current network namespace: because the network namespace is the initial network namespace, owned by root. And we're not root. The "YIELD" warning triangle sign is the indication that the effective capabilities of the process also apply to the target namespace. Which might be none, as in this example. Sigh.

For instance, a process inside a user-created user namespace (sic!) gains (all) capabilities ... how shockingly shocking! In the following example, the process is a user process inside the initial userspace and the target namespace is a network namespace inside the user-created user namespace (sic!). As user namespaces are designed, this grants the process all capabilities in the network namespace.

⛛ user:[4026531837] process "systemd" (129419)
├─ process "nscaps" (210373)
│     ⋄─ (no capabilities)
└─ ✓ user:[4026532342] process "unshare" (176744)
   └─ target net:[4026532353] process "unshare" (176744)
        ⋄─ cap_audit_control    cap_audit_read       cap_audit_write      cap_block_suspend
        ⋄─ cap_chown            cap_dac_override     cap_dac_read_search  cap_fowner
        ⋄─ cap_fsetid           cap_ipc_lock         cap_ipc_owner        cap_kill
        ⋄─ cap_lease            cap_linux_immutable  cap_mac_admin        cap_mac_override
        ⋄─ cap_mknod            cap_net_admin        cap_net_bind_service cap_net_broadcast
        ⋄─ cap_net_raw          cap_setfcap          cap_setgid           cap_setpcap
        ⋄─ cap_setuid           cap_sys_admin        cap_sys_boot         cap_sys_chroot
        ⋄─ cap_sys_module       cap_sys_nice         cap_sys_pacct        cap_sys_ptrace
        ⋄─ cap_sys_rawio        cap_sys_resource     cap_sys_time         cap_sys_tty_config
        ⋄─ cap_syslog           cap_wake_alarm

Please note how the user namespace enclosing the specified namespace now carries a friendly check mark: our process will gain all capabilities when entering "user:[4026532342]". And in consequence, our process also has all capabilities in the specified target network namespace.

But there are also cases where we're lost: if we ask for capabilities in the initial network namespace while inside the user-defined user namespace, then this will be shown instead:

⛔ user:[4026531837] process "systemd" (211474)
├─ ⛛ user:[4026532468] process "unshare" (219837)
│  └─ process "unshare" (219837)
│        ⋄─ cap_audit_control    cap_audit_read       cap_audit_write      cap_block_suspend
│        ⋄─ cap_chown            cap_dac_override     cap_dac_read_search  cap_fowner
│        ⋄─ cap_fsetid           cap_ipc_lock         cap_ipc_owner        cap_kill
│        ⋄─ cap_lease            cap_linux_immutable  cap_mac_admin        cap_mac_override
│        ⋄─ cap_mknod            cap_net_admin        cap_net_bind_service cap_net_broadcast
│        ⋄─ cap_net_raw          cap_setfcap          cap_setgid           cap_setpcap
│        ⋄─ cap_setuid           cap_sys_admin        cap_sys_boot         cap_sys_chroot
│        ⋄─ cap_sys_module       cap_sys_nice         cap_sys_pacct        cap_sys_ptrace
│        ⋄─ cap_sys_rawio        cap_sys_resource     cap_sys_time         cap_sys_tty_config
│        ⋄─ cap_syslog           cap_wake_alarm
└─ target net:[4026531905] process "systemd" (211474)
    ⋄─ (no capabilities)

Now, the initial user namespace is marked with a "DO NOT ENTER" sign: it is inaccessible, including its own network namespace. Also note how our process gains all capabilities in our user namespace, yet it cannot apply these "power caps" to things outside its restricted view.

But even if we would create an additional user namespace in it which we then own, it wouldn't work either: still no access, as user namespaces categorically deny any access to parent and sibling (user) namespaces.

⛔ user:[4026531837] process "systemd" (211474)
├─ ⛛ user:[4026532468] process "unshare" (219837)
│  └─ process "unshare" (219837)
│        ⋄─ cap_audit_control    cap_audit_read       cap_audit_write      cap_block_suspend
│        ⋄─ cap_chown            cap_dac_override     cap_dac_read_search  cap_fowner
│        ⋄─ cap_fsetid           cap_ipc_lock         cap_ipc_owner        cap_kill
│        ⋄─ cap_lease            cap_linux_immutable  cap_mac_admin        cap_mac_override
│        ⋄─ cap_mknod            cap_net_admin        cap_net_bind_service cap_net_broadcast
│        ⋄─ cap_net_raw          cap_setfcap          cap_setgid           cap_setpcap
│        ⋄─ cap_setuid           cap_sys_admin        cap_sys_boot         cap_sys_chroot
│        ⋄─ cap_sys_module       cap_sys_nice         cap_sys_pacct        cap_sys_ptrace
│        ⋄─ cap_sys_rawio        cap_sys_resource     cap_sys_time         cap_sys_tty_config
│        ⋄─ cap_syslog           cap_wake_alarm
└─ ⛔ user:[4026532470] process "unshare" (351974)
   └─ target net:[4026532473] process "unshare" (351974)
         ⋄─ (no capabilities)

Insufficient Capabilities

When nscaps is started without the necessary privileges (in particular, the CAP_SYS_PTRACE capability) it has only limited visibilty onto Linux kernel namespaces. In this situation nscaps cannot determine the capabilities when either the specified process or specified namespace is totally out of reach from nscap's perspective.

Colorization

Unless specified otherwise using the "--color=none" flag, nscaps colorizes its output in order to make different types of namespaces easier to differentiate. Colorization gets disabled if nscaps detects that stdout isn't connected to a terminal, such as when piping into tools like "less".

Out of the box (or rather, Gopher hole), nscaps supports two color themes, called "dark" and "light". Default is the dark theme, but it can be changed using "--theme light". In order to set a theme permanently, and to optionally adapt it later to personal preferences, the selected theme can be written to stdout:

nscaps --theme light --dump > ~/.lxknsrc.yaml

For each type of Linux-kernel namespace the styling file "~.lxknsrc.yaml" contains a top-level element:

user:
pid:
cgroup:
ipc:
mnt:
net:
uts:

Additional output elements can also be styled:

process: # process names
owner:   # owner UIDs and user names
unknown: # unknown PIDs and PID namespaces

For each top-level element the foreground and background colors can be set independently, as well as several different type face and font rendering attributes. If the foreground and/or background color(s) or a specific attribute are not specified, then the terminal defaults apply.

Colors and attributes need to be specified in form of YAML list members, introduced with a "-" dash. Colors can be specified either in #RRGGBB format, or alternatively as ANSI colors (0-255). Make sure to always enclose color values in (single or double) quotes.

For example:

pid:
- bold
- foreground: '#aabbcc'

The following attributes are supported, but are subject to specific terminal implementations rendering them:

• blink
• bold
• crossout
• faint
• italic
• italics
• overline
• reverse
• underline