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 binary. In that case, the security implications are
-minimal.
+on the mtr-packet binary. In that case, the security implications are
+minimal.
-Or you can make mtr setuid-root, and the following applies to you....
-Since mtr is installed as suid-root, some concern over security is
-justified. Since version 0.21, mtr does the following two things
-after it is launched:
+3. Make mtr-packet a setuid-root binary.
-* mtr requests a pair of raw sockets from the kernel.
-* mtr drops root privileges by setting the effective uid to match
- uid or the user calling mtr.
+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.
-See main() in mtr.c and net_preopen() in net.c for the details of this
-process. Note that no code from GTK+ or curses is executed before
-dropping root privileges.
+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:
-This should severely limit the possibilities of using mtr to breach
-system security. This means the worst case scenerio is as follows:
+* 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.
-Due to some oversight in the mtr code, a malicious user is able to
-overrun one of mtr's internal buffers with binary code that is
+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 which they wouldn't normally have
-permission to read or write to, repectively. The only privilege
-gained is access to the raw socket descriptors, which would allow
-the malicious user to listen to all ICMP packets arriving at the
-system, and to send forged packets with arbitrary contents.
-
-The mtr-code does its best to prevent calling of external library
-code before dropping privileges. It seems that C++ library code has
-the ability to issue a "please execute me before calling main" to the
-loader/linker. That would mean that we're still vulnerable to
-errors in that code. This is why I would prefer to drop the backends,
-have mtr-core always run in "raw" mode, and have the backends interpret
-the output from the mtr-core. Maybe a nice project for a college-level
-student.
+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 direct them to the mtr mailing list. See README for details.
+please see the README file for details on how to submit them.
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