posix-caps-ng

node.js wrapper for the libcap-ng POSIX capabilities library

npm install posix-caps-ng
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This is a node.js module that provides libcap-ng bindings to modify the capabilities of the current process.

The most likely use for this is obviously setting CAP_NET_BIND_SERVICE to enable binding to privileged ports such as 80 or 443.

To use a capability this the user running the program needs to have the capability, too. This can be achieved by using pam_cap and granting the capability via the /etc/security/capability.conf file.

Unfortunately the node binary also needs the capability - but only in its inheritable set. Executing setcap cap_net_bind_service+i /usr/bin/node as root does the job.

Usage:

var caps = require('posix-caps-ng');
caps.set_cap(caps.CAP_NET_BIND_SERVICE, caps.EFFECTIVE, true);

If the application does not start any child processes which also need this cap, it is a good idea to clear it from the inheritable set after enabling it and possibly also removing the cap altogether after binding to the privileged port:

caps.set_cap(caps.CAP_NET_BIND_SERVICE, caps.ALL, false);

Functions

  • bool has_cap(cap, type) - check if the given cap is set
  • bool set_cap(cap, types, set) - set/remove the given cap
  • bool clear_caps() - remove all caps
  • string get_caps(type) - get a string containing all set caps

type can be one of caps.EFFECTIVE, caps.PERMITTED, caps.INHERITABLE.
types can be any combination (binary OR) of those flags.

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