Messages in this thread Patch in this message |  | | Date | Tue, 19 Nov 2013 08:46:27 -0500 | From | Peter Hurley <> | Subject | Re: [PATCH] tty: Only hangup once |
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On 11/18/2013 04:09 PM, Heorhi Valakhanovich wrote: > On Mon, 18 Nov 2013 15:32:59 -0500 > Peter Hurley <peter@hurleysoftware.com> wrote: > >> On 11/18/2013 12:37 PM, Peter Hurley wrote: >>> On 11/18/2013 08:42 AM, One Thousand Gnomes wrote: >>>>> After upgrading to kernel 3.12 I noticed one issue with tmux >>>>> software. The easiest way to reproduce will be: >>>>> 1. Start tmux session as root. >>>>> 2. Connect via ssh and use "tmux attach" to attach to the running >>>>> session. >>>>> 3. Kill ssh client. >>> >>> Heorhi, >>> >>> Thanks for the report. >>> >>>>> You can notice that shell (zsh in my case) and "tmux attach" are >>>>> still remains in process' list. That didn't happen in previous >>>>> kernels. >> >> Heorhi, >> >> I could not reproduce this behavior with zsh or bash. >> >> In case I misunderstood, the steps I took to reproduce were, >> >> [On ssh server machine running 3.12] >> 1. Add 'set-option -g default-shell /usr/bin/zsh' to /etc/tmux.conf > > This is really not necessary. I also reproduced it with bash. > >> 2a. In terminal window, 'sudo tmux' >> - also tried - >> 2b. At root login on tty2, 'tmux' >> >> Successfully starts tmux session. Then, >> >> [On ssh client machine] >> 1. 'ssh user@server' >> 2. 'sudo tmux attach' >> 3. Switch to 2nd terminal window, >> 4. ps -ef | grep ssh >> 5. kill $pid_from_step4 >> >> This *did not* leave the 'tmux attach' process alive. >> >> Is zsh your login shell as well? Maybe that's the required >> component to reproduce the behavior you've observed. >> >> Regards, >> Peter Hurley > > Thank you for your attention. > I tried to reproduce it exactly as you did and notice strange thing. > You use "sudo tmux attach" and tmux client uses the terminal created > for regular user and those works good. > > But if you will use "ssh root@server" (you can use localhost too) the > "tmux attach" will use terminal created from root (i checked this with > lsof and ls -al /dev/pts) and behavior is different. Are terminals > created for root is somehow different from those created for regular > users? > > If you can't use root ssh login I will try to reproduce it's for sudo by > mixing some kind of dtach and tmux but it will be very unclear at the > end.
Thanks for the additional testing; yes, the "ssh root@server" is the crucial difference. I was able to reproduce the problem immediately.
Before sshd execs a new root shell, it hangs up and then re-opens the current tty as a security measure. Because the tty state was not being reset, the subsequent re-open could not be hung up.
Would you please test the patch below and confirm the fix?
--->%--- Subject: [PATCH] tty: Reset hupped state on open
A common security idiom is to hangup the current tty (via vhangup()) after forking but before execing a root shell. This hangs up any existing opens which other processes may have and ensures subsequent opens have the necessary permissions to open the root shell tty/pty.
Reset the TTY_HUPPED state after the driver has successfully returned the opened tty (perform the reset while the tty is locked to avoid racing with concurrent hangups).
Reported-by: Heorhi Valakhanovich <valahanovich@tut.by> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> --- drivers/tty/tty_io.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 3a1a01a..c74a00a 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2086,6 +2086,7 @@ retry_open: filp->f_op = &tty_fops; goto retry_open; } + clear_bit(TTY_HUPPED, &tty->flags); tty_unlock(tty);
-- 1.8.1.2
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