linux-kernel - Re: [PATCH] tty: Fix SIGTTOU not sent with tcflush()

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Date:	Fri, 27 Sep 2013 07:19:53 +0200
From:	Karel Srot <ksrot@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	codonell <codonell@...hat.com>, Eduard Benes <ebenes@...hat.com>,
	Matt Newsome <mnewsome@...hat.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] tty: Fix SIGTTOU not sent with tcflush()

Hello Oleg,

On Thu, 2013-09-26 at 21:10 +0200, Oleg Nesterov wrote:
> On 09/26, Oleg Nesterov wrote:
> >
> > Thanks Peter.
> >
> > Well. I'am afraid my testing was wrong, because Karel reports
> > it fixes the problem...
> >
> > But. I applied this patch to my 3.11 tree (last commit is bff157b3a)
> > which also has the additional patch (03e12617 "tty: disassociate_ctty()
> > sends the extra SIGCONT"), and
> >
> > 	TET_CONFIG=CFG TET_ROOT=.  ./T.tcflush 4
> >
> > still fails... T.tcflush was compiled on another (Karel's) machine,
> > perhaps there is something in libc, I do not know.
> >
> > So let me ask just in case, I assume the fix below doesn't depend on
> > other changes I could miss?
> >
> > I'll retest after git-pull and report...
> 
> Still fails under the Linus's tree + this patch.
> 
> However!!!
> 
> Tested-by: Oleg Nesterov <oleg@...hat.com>
> 
> 
> 
> 
> It turns out, T.tcflush doesn't expect it can start as a process group
> leader. In this case setsid() fails, then tty_open() doesn't set
> signal->tty, and thus this patch makes no difference: tty_check_change()
> fails because tty doesn't match signal->tty.
> 
> And indeed, this test passes if you run it under strace, or simply do
> 
> 	$ TET_CONFIG=CFG TET_ROOT=. perl -e "system './T.tcflush 4'"
> 
> And damn, the fact it doesn't fail under strace doesn't allow you to
> see that setsid() fails ;)
> 
> This is probably explains why Karel reported success, perhaps he
> didn't run this test individually.

This is true, I didn't execute this particular test directly but through
the LSB test suite framework.

> 
> Thanks again Peter. Perhaps my analysis was wrong (and I do not see
> setsid() in the sources), I do not really care. but perhaps tcflush.c
> should be updated.
> 
> Oleg.
> 


Karel

-- 
Karel Srot
Quality Engineer, QE BaseOS Security team

Email: ksrot@...hat.com
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic

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