From: ebiederm@xmission.com (Eric W. Biederman)
To: Oleg Nesterov <oleg@redhat.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: [PATCH v2] unshare: Unsharing a thread does not require unsharing a vm
Date: Wed, 12 Aug 2015 14:59:37 -0500 [thread overview]
Message-ID: <87wpx046s6.fsf_-_@x220.int.ebiederm.org> (raw)
In-Reply-To: <20150812174847.GA6703@redhat.com> (Oleg Nesterov's message of "Wed, 12 Aug 2015 19:48:47 +0200")
In the logic in the initial commit of unshare made creating a new
thread group for a process, contingent upon creating a new memory
address space for that process. That is wrong. Two separate
processes in different thread groups can share a memory address space
and clone allows creation of such proceses.
This is significant because it was observed that mm_users > 1 does not
mean that a process is multi-threaded, as reading /proc/PID/maps
temporarily increments mm_users, which allows other processes to
(accidentally) interfere with unshare() calls.
Correct the check in check_unshare_flags() to test for
!thread_group_empty() for CLONE_THREAD, CLONE_SIGHAND, and CLONE_VM.
For sighand->count > 1 for CLONE_SIGHAND and CLONE_VM.
For !current_is_single_threaded instead of mm_users > 1 for CLONE_VM.
By using the correct checks in unshare this removes the possibility of
an accidental denial of service attack.
Additionally using the correct checks in unshare ensures that only an
explicit unshare(CLONE_VM) can possibly trigger the slow path of
current_is_single_threaded(). As an explict unshare(CLONE_VM) is
pointless it is not expected there are many applications that make
that call.
Cc: stable@vger.kernel.org
Fixes: b2e0d98705e60e45bbb3c0032c48824ad7ae0704 userns: Implement unshare of the user namespace
Reported-by: Ricky Zhou <rickyz@chromium.org>
Reported-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
Reposting this change with the addition of the needed test for
sighand->count > 1.
kernel/fork.c | 28 ++++++++++++++++++----------
1 file changed, 18 insertions(+), 10 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index 1bfefc6f96a4..d544ae97f999 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1866,13 +1866,21 @@ 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_SIGHAND | CLONE_VM)) {
+ if (atomic_read(¤t->sighand->count) > 1)
+ return -EINVAL;
+ }
+ if (unshare_flags & CLONE_VM) {
+ if (!current_is_single_threaded())
return -EINVAL;
}
@@ -1941,16 +1949,16 @@ 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;
- /*
* If unsharing vm, must also unshare signal handlers.
*/
if (unshare_flags & CLONE_VM)
unshare_flags |= CLONE_SIGHAND;
/*
+ * If unsharing a signal handlers, must also unshare the signal queues.
+ */
+ if (unshare_flags & CLONE_SIGHAND)
+ unshare_flags |= CLONE_THREAD;
+ /*
* If unsharing namespace, must also unshare filesystem information.
*/
if (unshare_flags & CLONE_NEWNS)
--
2.2.1
next prev parent reply other threads:[~2015-08-12 20:06 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
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 ` Eric W. Biederman [this message]
2015-08-13 12:57 ` [PATCH v2] " 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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