From: Oleg Nesterov <oleg@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Dmitry Vyukov <dvyukov@google.com>,
Alexander Potapenko <glider@google.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
Eric Dumazet <edumazet@google.com>,
Jan Kratochvil <jan.kratochvil@redhat.com>,
Julien Tinnes <jln@google.com>, Kees Cook <keescook@google.com>,
Kostya Serebryany <kcc@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
Pedro Alves <palves@redhat.com>,
Robert Swiecki <swiecki@google.com>,
Roland McGrath <roland@hack.frob.com>,
syzkaller@googlegroups.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] wait/ptrace: always assume __WALL if the child is traced
Date: Wed, 21 Oct 2015 19:41:50 +0200 [thread overview]
Message-ID: <20151021174150.GA24546@redhat.com> (raw)
In-Reply-To: <20151020153155.e03f4219da4014efe6f810b0@linux-foundation.org>
On 10/20, Andrew Morton wrote:
>
> On Tue, 20 Oct 2015 19:17:54 +0200 Oleg Nesterov <oleg@redhat.com> wrote:
>
> > The following program (simplified version of generated by syzkaller)
> >
> > #include <pthread.h>
> > #include <unistd.h>
> > #include <sys/ptrace.h>
> > #include <stdio.h>
> > #include <signal.h>
> >
> > void *thread_func(void *arg)
> > {
> > ptrace(PTRACE_TRACEME, 0,0,0);
> > return 0;
> > }
> >
> > int main(void)
> > {
> > pthread_t thread;
> >
> > if (fork())
> > return 0;
> >
> > while (getppid() != 1)
> > ;
> >
> > pthread_create(&thread, NULL, thread_func, NULL);
> > pthread_join(thread, NULL);
> > return 0;
> > }
> >
> > creates the unreapable zombie if /sbin/init doesn't use __WALL.
> >
> > This is not a kernel bug, at least in a sense that everything works as
> > expected: debugger should reap a traced sub-thread before it can reap
> > the leader, but without __WALL/__WCLONE do_wait() ignores sub-threads.
> >
> > Unfortunately, it seems that /sbin/init in most (all?) distributions
> > doesn't use it and we have to change the kernel to avoid the problem.
>
> Well, to fix this a distro needs to roll out a new kernel. Or a new
> init(8). Is there any reason to believe that distributing/deploying a
> new kernel is significantly easier for everyone? Because fixing init
> sounds like a much preferable solution to this problem.
I will be happy if we decide that this is userpace problem and we should
not fix the kernel. I simply do not know.
However, please look at 2/2 which imho makes sense regardless and looks
"obviously safe". Without this patch waitid() can not use __WALL, so if
/sbin/init uses waitid() then the userspace fix won't be one-liner. And
at least Fedora22 and Ubuntu use waitid().
So personally I'd prefer 2/2 + fix-init, not sure if this can work...
Oleg.
next prev parent reply other threads:[~2015-10-21 17:45 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-20 17:17 [PATCH 0/2] wait/ptrace: always assume __WALL if the child is traced Oleg Nesterov
2015-10-20 17:17 ` [PATCH 1/2] " Oleg Nesterov
2015-10-20 22:31 ` Andrew Morton
2015-10-21 3:27 ` Vasily Averin
2015-10-21 17:41 ` Oleg Nesterov [this message]
2015-10-21 19:47 ` Andrew Morton
2015-10-21 20:44 ` Oleg Nesterov
2015-10-21 19:59 ` Denys Vlasenko
2015-10-21 20:31 ` Denys Vlasenko
2015-10-21 21:47 ` Oleg Nesterov
2015-10-21 23:27 ` Denys Vlasenko
2015-10-25 15:54 ` Oleg Nesterov
2015-10-26 12:08 ` Pedro Alves
2015-10-28 16:11 ` Oleg Nesterov
2015-10-28 15:43 ` Pedro Alves
2015-10-28 19:02 ` Oleg Nesterov
2015-10-22 13:51 ` Denys Vlasenko
2015-10-20 17:17 ` [PATCH 2/2] wait: allow sys_waitid() to use __WNOTHREAD/__WCLONE/__WALL Oleg Nesterov
2015-10-20 17:36 ` [PATCH 0/2] wait/ptrace: always assume __WALL if the child is traced Oleg Nesterov
2015-10-22 14:40 ` Pedro Alves
2015-10-25 15:42 ` Oleg Nesterov
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