This is a note to let you know that I've just added the patch titled

pidns: disable pid allocation if pid_ns_prepare_proc() is failed in alloc_pid()

to the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: pidns-disable-pid-allocation-if-pid_ns_prepare_proc-is-failed-in-alloc_pid.patch and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Tue Apr 10 13:58:07 CEST 2018

From: Kirill Tkhai ktkhai@virtuozzo.com Date: Mon, 8 May 2017 15:56:34 -0700 Subject: pidns: disable pid allocation if pid_ns_prepare_proc() is failed in alloc_pid()

From: Kirill Tkhai ktkhai@virtuozzo.com

[ Upstream commit 8896c23d2ef803f1883fea73117a435925c2b4c4 ]

alloc_pidmap() advances pid_namespace::last_pid. When first pid allocation fails, then next created process will have pid 2 and pid_ns_prepare_proc() won't be called. So, pid_namespace::proc_mnt will never be initialized (not to mention that there won't be a child reaper).

I saw crash stack of such case on kernel 3.10:

BUG: unable to handle kernel NULL pointer dereference at (null) IP: proc_flush_task+0x8f/0x1b0 Call Trace: release_task+0x3f/0x490 wait_consider_task.part.10+0x7ff/0xb00 do_wait+0x11f/0x280 SyS_wait4+0x7d/0x110

We may fix this by restore of last_pid in 0 or by prohibiting of futher allocations. Since there was a similar issue in Oleg Nesterov's commit 314a8ad0f18a ("pidns: fix free_pid() to handle the first fork failure"). and it was fixed via prohibiting allocation, let's follow this way, and do the same.

Link: http://lkml.kernel.org/r/149201021004.4863.6762095011554287922.stgit@localho... Signed-off-by: Kirill Tkhai ktkhai@virtuozzo.com Acked-by: Cyrill Gorcunov gorcunov@openvz.org Cc: Andrei Vagin avagin@virtuozzo.com Cc: Andreas Gruenbacher agruenba@redhat.com Cc: Kees Cook keescook@chromium.org Cc: Michael Kerrisk mtk.manpages@googlemail.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Oleg Nesterov oleg@redhat.com Cc: Paul Moore paul@paul-moore.com Cc: Eric Biederman ebiederm@xmission.com Cc: Andy Lutomirski luto@amacapital.net Cc: Ingo Molnar mingo@kernel.org Cc: Serge Hallyn serge@hallyn.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/pid.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/pid.c +++ b/kernel/pid.c @@ -316,8 +316,10 @@ struct pid *alloc_pid(struct pid_namespa }

if (unlikely(is_child_reaper(pid))) { - if (pid_ns_prepare_proc(ns)) + if (pid_ns_prepare_proc(ns)) { + disable_pid_allocation(ns); goto out_free; + } }

get_pid_ns(ns);

Patches currently in stable-queue which might be from ktkhai@virtuozzo.com are

queue-3.18/pidns-disable-pid-allocation-if-pid_ns_prepare_proc-is-failed-in-alloc_pid.patch