ping not working in a chroot

Question

How can I use the ping command in a chroot environment?

$ ping 8.8.8.8
ping: icmp open socket: Operation not permitted

Currently I am using CentOs, but ideally there must be a solution that works in all chrooted environments.

Solution 1

Under Linux, ping needs to run as root (because it needs to bind a raw IP socket; ordinary users can only do UDP and TCP). It's designed to be setuid root. It looks like your copy in the chroot isn't setuid root. Fix the permissions:

chown root:root /bin/ping; chmod u+srwx,go=rx /bin/ping

Note that there may be other commands in the chroot that need to be setuid (or setgid), in particular su and sudo.

Note that this answers assumes a chroot, not something with more restrictions like a jail.

Solution 2

As have been pointed out, ping needs the permission to bind a raw IP socket. Traditionally setuid has been used to allow normal users to use it. However, using capabilities (POSIX 1003.1e, capabilities(7)), a minimal set of capabilities can be selectively enabled, limiting the security consequences of potential vulnerabilities.

ping needs the capability CAP_NET_RAW. Suppose that the path to the binary is /usr/bin/ping, the capability can be set using the tool setcap:

setcap cap_net_raw+ep /usr/bin/ping

Use getcap to check the result:

getcap /usr/bin/ping

The output should be something like

/usr/bin/ping = cap_net_raw+ep

and ping should work now.

Comments

[Gilles 'SO- stop being evil']

What happens when you try?

[umeboshi]

This should be the accepted answer. Thank you for helping me!

[geerlingguy]

Or as an octal, chmod 4755 /bin/ping.

[user_dev]

this does not work in a chroot environment as the user will not have the root permission.