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pidns: fix vfork() after unshare(CLONE_NEWPID)

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commit e79f525e99b04390ca4d2366309545a836c03bf1 upstream.

Commit 8382fcac1b ("pidns: Outlaw thread creation after
unshare(CLONE_NEWPID)") nacks CLONE_VM if the forking process unshared
pid_ns, this obviously breaks vfork:

	int main(void)
	{
		assert(unshare(CLONE_NEWUSER | CLONE_NEWPID) == 0);
		assert(vfork() >= 0);
		_exit(0);
		return 0;
	}

fails without this patch.

Change this check to use CLONE_SIGHAND instead.  This also forbids
CLONE_THREAD automatically, and this is what the comment implies.

We could probably even drop CLONE_SIGHAND and use CLONE_THREAD, but it
would be safer to not do this.  The current check denies CLONE_SIGHAND
implicitely and there is no reason to change this.

Eric said "CLONE_SIGHAND is fine.  CLONE_THREAD would be even better.
Having shared signal handling between two different pid namespaces is
the case that we are fundamentally guarding against."

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Colin Walters <walters@redhat.com>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Oleg Nesterov 2013-09-11 14:19:38 -07:00 committed by Greg Kroah-Hartman
parent 5a48788ca4
commit f608ebd760
1 changed files with 4 additions and 3 deletions
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7
kernel/fork.c
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@ -1171,10 +1171,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
return ERR_PTR(-EINVAL); return ERR_PTR(-EINVAL);
/* /*
* If the new process will be in a different pid namespace * If the new process will be in a different pid namespace don't
* don't allow the creation of threads. * allow it to share a thread group or signal handlers with the
* forking task.
*/ */
if ((clone_flags & (CLONE_VM|CLONE_NEWPID)) && if ((clone_flags & (CLONE_SIGHAND | CLONE_NEWPID)) &&
(task_active_pid_ns(current) != current->nsproxy->pid_ns)) (task_active_pid_ns(current) != current->nsproxy->pid_ns))
return ERR_PTR(-EINVAL); return ERR_PTR(-EINVAL);