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Trace sshd

A collection of BCC scripts to trace some events in OpenSSH's sshd.

The bpftrace scripts were just prototypes for the BCC scripts.

Scripts

with_syscalls

Scripts to trace sshd by only examining the syscalls it makes

trace_authorizedkeyscommand

Trace each time the AuthorizedKeysCommand is ran, how much time it took and for which user it was done. Also each time an authentication finishes, display who was the user and whether the auth succeeded.

Screenshots

sshd_authorizedkeyscommand_ran{username="martin", duration_ms=1010.226717}
sshd_authorizedkeyscommand_ran{username="martin", duration_ms=1007.266651}
sshd_auth_finished{username="martin", success=1}

As we can see from the screenshot above, the AuthorzedKeysCommand was ran twice and the user 'martin' was authenticated successfully.

with_symbols

Scripts to trace sshd that require sshd to not be stripped. Also make uses of unstable APIs.

trace_sessions

Collect stats of sessions as they end.

WARNING: For now the script is dependant on the fact that the authkeyscommand is '/usr/local/bin/ssh-auth.sh %u'

Screenshots

/-----------------------------------------------------------------------\
|       USERNAME       |  RECV (B)  |  SENT (B)  |      TIME (ms)       |
|        martin        |    1343488 |    3342964 |                11171 |
|         root         |    4571136 |   16851732 |                10388 |
^C----------------------------------------------------------------------/

trace_authorizedkeyscommand

Collect stats about the auth with the 'AuthorizedKeysCommand' program.

Screenshots

/--------------------------------------------------\
|       USERNAME       |  SUCCESS   | TIME TO AUTH |
|        martin        |     1      |     2011     |
|        martin        |     1      |     9370     |
|         root         |     0      |     2008     |
^C-------------------------------------------------/

Shortcomings

  • Needs a non-stripped sshd
  • sshd must be located in /usr/bin/sshd
  • Uses eBPF uprobes and structs definitions taken from the OpenSSH source code. This is a very unstable API to trace and is prone to breaking with every OpenSSH update.

How to run

Just do

sudo ./<script>.py

Requirements

  • sshd
  • bcc
  • python-bcc