lkml.org 
[lkml]   [2007]   [Nov]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch] PID namespace design bug, workaround
Ingo Molnar wrote:
> while checking recent commits to the kernel core i took a look at the
> PID namespaces implementation, and it has a fatal flaw: it breaks
> futexes and various libraries (and other stuff) that use PIDs as the
> means of identifying tasks, by not providing any means of global
> identification that works across PID namespaces. (PIDs _are_ a very

You're not 100% correct here. The task_pid_nr() does return you a
unique pid, so you do have the way to identify the task.

Another thing - you should *not* allow tasks to communicate across
pid namespaces using any pids - this just breaks the pid namespaces
idea.

As far as the futexes are concerned - I do not allow threads live
in different pid namespaces (more correct fix would be not to allow
tasks share the mm_struct across pid namespaces, but this is a one
line fix), so the situation when you have two threads in different
namespaces is impossible.

Thanks,
Pavel

> convenient and global way of identifying contexts.)
>
> i asked Ulrich about this and it turns out he has warned about this
> early on:
>
> http://www.nabble.com/Re%3A-question%3A-pid-space-semantics.-p3409990.html
>
> but this problem is still present in the code, and it has been recently
> committed into mainline via:
>
> commit 30e49c263e36341b60b735cbef5ca37912549264
> Author: Pavel Emelyanov <xemul@openvz.org>
> Date: Thu Oct 18 23:40:10 2007 -0700
>
> pid namespaces: allow cloning of new namespace
>
> without these problems having been resolved. A full-scale revert is
> probably too intrusive, but at minimum we need to turn off user-space
> access to this feature via this simple patch. Until this issue is
> resolved properly the new PID namespace code needs to be turned off.
> Letting this into 2.6.24 would be a disaster.
>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> ---
> kernel/fork.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> Index: v/kernel/fork.c
> ===================================================================
> --- v.orig/kernel/fork.c
> +++ v/kernel/fork.c
> @@ -1420,6 +1420,14 @@ long do_fork(unsigned long clone_flags,
> int trace = 0;
> long nr;
>
> + /*
> + * PID namespaces are broken at the moment: they do not allow
> + * certain PID based syscalls (such as futexes) to be used
> + * across namespaces. This is broken and must not be allowed,
> + * so we keep this feature turned off until it's properly fixed.
> + */
> + clone_flags &= ~CLONE_NEWPID;
> +
> if (unlikely(current->ptrace)) {
> trace = fork_traceflag (clone_flags);
> if (trace)
>

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-11-01 16:05    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site