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 --- kernel/pid.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/pid.c b/kernel/pid.c index 693a64385d59..fa704f88ff8e 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -322,8 +322,10 @@ struct pid *alloc_pid(struct pid_namespace *ns) }
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);