SECURITY

SECURITY ISSUES RELATED TO MTR

mtr invokes a sub-process, mtr-packet, which requires extra privileges
to send custom packets, and there are security implications from
granting this.

There are several different ways to provide the privileges:

1. Add limited privileges on systems that support this. (Preferred.)
2. Run mtr as the root user.
3. Make mtr-packet a setuid-root binary.

Details:

1. Add limited privileges on systems that support this.

Some operating systems allow binaries to be run with only the subset
of security privileges that are actually needed.

Linux:
On Linux, privileges are known as capabilities. The only additional
capability that mtr-packet needs is cap_net_raw. To give this
capability to the mtr-packet binary, run the following command as root:

# setcap cap_net_raw+ep mtr-packet


2. Run mtr as the root user.

You can limit mtr usage to the root user by not putting a setuid bit
on the mtr-packet binary. In that case, the security implications are
minimal.


3. Make mtr-packet a setuid-root binary.

The mtr-packet binary can be made setuid-root, which is what "make install"
does only if using setcap (above) fails.  Using setcap is tried first.

When mtr-packet is installed as suid-root, some concern over security is
justified.  mtr-packet does the following two things after it is launched:

*  mtr-packet open sockets for sending raw packets and for receiving
   ICMP packets.
*  mtr-packet drops root privileges by setting the effective uid to
   match uid or the user calling mtr.
*  If capabilities support is available, mtr-packet drops all privileged
   capabilities.

See main() in packet.c and init_net_state_privileged() in probe_unix.c
for the details of this process.

This should limit the possibilities of using mtr to breach system security.
The worst case scenario is as follows:

Due to some oversight in the mtr-packet code, a malicious user is able to
overrun one of mtr-packets's internal buffers with binary code that is
eventually executed.  The malicious user is still not able to read
from or write to any system files other than those normally accessible
by the user running mtr.  The only privileges gained are access to the raw
socket, which would allow the malicious user to listen to all ICMP packets
arriving at the system, and to send forged packets with arbitrary contents.


If you have further questions or comments about security issues,
please see the README file for details on how to submit them.