lkml.org 
[lkml]   [2018]   [Apr]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH 4.9 022/310] pidns: disable pid allocation if pid_ns_prepare_proc() is failed in alloc_pid()
    Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:

    > 4.9-stable review patch. If anyone has any objections, please let me
    > know.

    No objections but if you are grabbing that one please check if you
    have it's follow on fix.

    c0ee554906c3 ("pid: Handle failure to allocate the first pid in a pid namespace")

    There were a few cases not handled but the fix below, that made a more
    comprehensive fix desirable.

    Eric

    > ------------------
    >
    > 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@localhost.localdomain
    > 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
    > @@ -322,8 +322,10 @@ 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);

    \
     
     \ /
      Last update: 2018-04-11 21:29    [W:3.665 / U:0.200 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site