Date: Sun, 21 May 2023 11:40:47 -0700 From: bob prohaska <fbsd@www.zefox.net> To: freebsd-current@freebsd.org Cc: bob prohaska <fbsd@www.zefox.net> Subject: Re: Stray characters in command history Message-ID: <ZGplr9GJii3eI6RP@www.zefox.net> In-Reply-To: <ZGohbTVTRwfJkqyk@www.zefox.net> References: <ZGohbTVTRwfJkqyk@www.zefox.net>
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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 > > >
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