From 8896c23d2ef803f1883fea73117a435925c2b4c4 Mon Sep 17 00:00:00 2001 From: Kirill Tkhai Date: Mon, 8 May 2017 15:56:34 -0700 Subject: pidns: disable pid allocation if pid_ns_prepare_proc() is failed in alloc_pid() 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@localhost.localdomain Signed-off-by: Kirill Tkhai Acked-by: Cyrill Gorcunov Cc: Andrei Vagin Cc: Andreas Gruenbacher Cc: Kees Cook Cc: Michael Kerrisk Cc: Al Viro Cc: Oleg Nesterov Cc: Paul Moore Cc: Eric Biederman Cc: Andy Lutomirski Cc: Ingo Molnar Cc: Serge Hallyn Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/pid.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/pid.c b/kernel/pid.c index 0143ac0ddceb..fd1cde1e4576 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -321,8 +321,10 @@ 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); -- cgit v1.2.3