Messages in this thread | | | Date | Mon, 2 Jun 2008 12:39:29 +0200 | From | "Vegard Nossum" <> | Subject | Re: 2.6.25.3: su gets stuck for root |
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On Mon, Jun 2, 2008 at 12:16 PM, Vegard Nossum <vegard.nossum@gmail.com> wrote: > On Mon, Jun 2, 2008 at 11:20 AM, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote: >> On Mon, 02 Jun 2008 18:31:34 +0930 >> David Newall <davidn@davidnewall.com> wrote: >> >>> Alan Cox wrote: >>> > Not really. The task would get suspended if it attempted to change the >>> > tty settings while not being session leader. This is part of the POSIX >>> > and BSD job control. >>> >>> I haven't heard about this new restriction, but it begs the observation >>> that stty, when forked from a shell (the usual case), is never a session >>> leader. >> >> Sorry I mean part of the current session. I was thinking about the >> specific case of bash or the ssh->bash setup where the question would be >> whether the shell was session leader. >> >> Someone who can dup this needs to instrument it in tty_ioctl really. > > Hi, > > I have written a short test program that seems to reproduce it for me > (see attachment), even though the original su/stty stuff wouldn't. > > Basically, the strace shows this: > ioctl(0, SNDCTL_TMR_START or TCSETS, {B38400 opost isig icanon echo > ...}) = ? ERESTARTSYS (To be restarted) > --- SIGTTOU (Stopped (tty output)) @ 0 (0) --- > --- SIGTTOU (Stopped (tty output)) @ 0 (0) --- > ioctl(0, SNDCTL_TMR_START or TCSETS, {B38400 opost isig icanon echo > ...}) = ? ERESTARTSYS (To be restarted) > --- SIGTTOU (Stopped (tty output)) @ 0 (0) --- > --- SIGTTOU (Stopped (tty output)) @ 0 (0) --- > ... (repeating) > > The exact code path triggering this seems to be: > > tcsetattr() -> ioctl(TCSETS) -> set_termios() -> tty_check_change() > > This is on a 2.6.24.5-85.fc8 kernel. > > I don't know what's wrong, but I hope this helps.
The error seems that tty_check_change() returns -ERESTARTSYS. Shouldn't it be EINTR to allow the signal to be processed and let the process decide whether to retry the tcsetattr()?
Vegard
-- "The animistic metaphor of the bug that maliciously sneaked in while the programmer was not looking is intellectually dishonest as it disguises that the error is the programmer's own creation." -- E. W. Dijkstra, EWD1036
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