Re: Stray characters in command history

Here is another example, perhaps a bit clearer.

The ssh connection to the first Pi3 in the chain had dropped, so it was
re-establishing via a regular user login, then su was invoked and tip run:
.....
To change this login announcement, see motd(5).
Want to go the directory you were just in?
Type "cd -"
bob@pelorus:~ % su
Password:
# tip ucom
Stale lock on cuaU0 PID=2487... overriding.
connected
osed by r31 www s         <<<<  This appeared spontaneously, then I hit return.
osed: Command not found.  <<<<< I didn't type anything.
bob@www:/usr/src %        <<<<< The shell prompt on the 2nd Pi3's serial console.
....
Clearly nothing to do with sshd, might it simply be a misdirected echo of console
output generated by a (dead or broken) tip connection? The first example looked
possibly malicious, this does not....

Thanks for reading,

bob prohaska



On Sun, May 21, 2023 at 06:49:33AM -0700, bob prohaska wrote:
> Lately I've been playing with buildworld on a Pi3 running -current. The same machine
> acts as a terminal server for a second Pi3 also running -current in my "cluster". 
> I ssh into the first Pi3, su to root and run tip to pick up a serial connection to 
> the second Pi's console. Both machines are within a week of up-to-date.
> 
> While building world on the first Pi3 the ssh connection frequently drops and must be
> re-established. If there was a shell running on the serial console of the second
> Pi3 it typically keeps running and when the tip session is restarted disgorges a
> stream of accumulated console message. 
> 
> This morning the same thing happened, but I noticed something odd. The stream of
> messages (all login failure announcements from ssh) ended with
> 
> ....
> May 21 06:15:00 www sshd[33562]: error: Fssh_kex_exchange_identification: banner line contains invalid characters
> *+May 21 06:15:19 www sshd[33565]: error: Fssh_kex_exchange_identification: Connection closed by remote host
> May 21 06:15:33 www sshd[33613]: error: Protocol major versions differ: 2 vs. 1
> 
> At that point I hit carriage return and got
> *+: No match.
> 
> I did not type the *+ so it looks like the characters were somehow introduced elsewhere,
> possibly from the ssh failure message. How they got into the command stream is unclear.
> 
> This strikes me as undesirable at best and possibly much worse. The shell reporting
> the "no match" was a regular user shell, but if I'd been su'd to root it appears that
> the unmatched characters would be seen by the root shell as input.
> 
> This more-or-less fits with the pattern seen earlier with reboots observed via serial
> console halting on un-typed keystrokes. Those halts were attributed to electrical noise
> on the serial line, but this looks like something injected via part of the network
> login process. Reboot pauses have been an ongoing phenomenon for months, this is the 
> first time I've noticed the "invalid characters" message from ssh on the console.
> 
> Thanks for reading, apologies if I'm being a worrywart.
> 
> bob prohaska
> 
>  
>