From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
Andrew Morton <akpm@linux-foundation.org>,
Kees Cook <keescook@chromium.org>,
David Howells <dhowells@redhat.com>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Rik van Riel <riel@redhat.com>,
Vladimir Davydov <vdavydov@parallels.com>,
Ricky Zhou <rickyz@chromium.org>, Julien Tinnes <jln@google.com>
Subject: Re: [PATCH 1/2] unshare: Unsharing a thread does not require unsharing a vm
Date: Wed, 12 Aug 2015 19:48:47 +0200 [thread overview]
Message-ID: <20150812174847.GA6703@redhat.com> (raw)
In-Reply-To: <87vbclb8op.fsf_-_@x220.int.ebiederm.org>
On 08/11, Eric W. Biederman wrote:
>
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1866,13 +1866,17 @@ static int check_unshare_flags(unsigned long unshare_flags)
> CLONE_NEWUSER|CLONE_NEWPID))
> return -EINVAL;
> /*
> - * Not implemented, but pretend it works if there is nothing to
> - * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
> - * needs to unshare vm.
> + * Not implemented, but pretend it works if there is nothing
> + * to unshare. Note that unsharing the address space or the
> + * signal handlers also need to unshare the signal queues (aka
> + * CLONE_THREAD).
> */
> if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
> - /* FIXME: get_task_mm() increments ->mm_users */
> - if (atomic_read(¤t->mm->mm_users) > 1)
> + if (!thread_group_empty(current))
> + return -EINVAL;
> + }
> + if (unshare_flags & CLONE_VM) {
> + if (!current_is_single_threaded())
> return -EINVAL;
> }
OK, but then you can remove "| CLONE_VM" from the previous check...
> @@ -1941,16 +1945,16 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
> if (unshare_flags & CLONE_NEWUSER)
> unshare_flags |= CLONE_THREAD | CLONE_FS;
> /*
> - * If unsharing a thread from a thread group, must also unshare vm.
> - */
> - if (unshare_flags & CLONE_THREAD)
> - unshare_flags |= CLONE_VM;
OK,
> /*
> + * If unsharing a signal handlers, must also unshare the signal queues.
> + */
> + if (unshare_flags & CLONE_SIGHAND)
> + unshare_flags |= CLONE_THREAD;
This looks unnecessary, check_unshare_flags() checks "THREAD | SIGHAND".
And to me the comment looks misleading although I won't argue.
And in fact this doesn't look exactly right, or I am totally confused.
Shouldn't we do
if (unshare_flags & CLONE_SIGHAND)
unshare_flags |= CLONE_VM;
? Or change check_unshare_flags()...
Otherwise suppose that a single threaded process does clone(VM | SIGHAND)
and (say) child does sys_unshare(SIGHAND). This will wrongly succeed afaics.
Oleg.
next prev parent reply other threads:[~2015-08-12 17:51 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-28 17:15 [PATCH] user_ns: use correct check for single-threadedness Kees Cook
2015-07-28 18:02 ` Rik van Riel
2015-07-28 18:17 ` Eric W. Biederman
2015-07-28 20:55 ` Ricky Zhou
2015-07-28 21:01 ` Kees Cook
2015-08-05 18:13 ` Eric W. Biederman
2015-08-05 19:40 ` Kees Cook
2015-07-28 21:35 ` Andrew Morton
2015-07-28 21:50 ` Kees Cook
2015-07-28 22:11 ` Kirill A. Shutemov
2015-08-05 11:38 ` Ingo Molnar
2015-08-05 11:53 ` Kirill A. Shutemov
2015-08-05 13:13 ` Ricky Zhou
2015-08-05 17:23 ` Oleg Nesterov
2015-08-05 18:00 ` Eric W. Biederman
2015-08-05 18:52 ` Eric W. Biederman
2015-08-06 13:06 ` Oleg Nesterov
2015-08-06 13:44 ` Oleg Nesterov
2015-08-12 1:17 ` Eric W. Biederman
2015-08-12 14:40 ` Oleg Nesterov
2015-08-12 15:11 ` Eric W. Biederman
2015-08-12 1:22 ` [PATCH 0/2] userns: Creation logic fixes Eric W. Biederman
2015-08-12 1:24 ` [PATCH 1/2] unshare: Unsharing a thread does not require unsharing a vm Eric W. Biederman
2015-08-12 17:48 ` Oleg Nesterov [this message]
2015-08-12 18:39 ` Eric W. Biederman
2015-08-13 12:55 ` Oleg Nesterov
2015-08-13 15:38 ` Eric W. Biederman
2015-08-13 16:17 ` Oleg Nesterov
2015-08-13 16:27 ` Eric W. Biederman
2015-08-13 16:50 ` Oleg Nesterov
2015-08-14 17:59 ` Oleg Nesterov
2015-08-12 19:59 ` [PATCH v2] " Eric W. Biederman
2015-08-13 12:57 ` Oleg Nesterov
2015-08-13 16:01 ` Eric W. Biederman
2015-08-13 16:30 ` Oleg Nesterov
2015-08-13 16:39 ` Eric W. Biederman
2015-08-12 1:25 ` [PATCH 2/2] userns,pidns: Force thread group sharing, not signal handler sharing Eric W. Biederman
2015-08-12 17:24 ` Oleg Nesterov
2015-08-12 6:29 ` [PATCH 0/2] userns: Creation logic fixes Kees Cook
2015-08-06 14:35 ` [PATCH] user_ns: use correct check for single-threadedness Oleg Nesterov
2015-08-06 21:16 ` Eric W. Biederman
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