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Re: netlink: GPF in sock_sndtimeo

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On Fri, Dec 9, 2016 at 3:01 AM, Richard Guy Briggs <rgb@redhat.com> wrote:
> On 2016-12-08 22:57, Cong Wang wrote:
>> On Thu, Dec 8, 2016 at 10:02 PM, Richard Guy Briggs <rgb@redhat.com> wrote:
>> > I also tried to extend Cong Wang's idea to attempt to proactively respond to a
>> > NETLINK_URELEASE on the audit_sock and reset it, but ran into a locking error
>> > stack dump using mutex_lock(&audit_cmd_mutex) in the notifier callback.
>> > Eliminating the lock since the sock is dead anways eliminates the error.
>> >
>> > Is it safe?  I'll resubmit if this looks remotely sane.  Meanwhile I'll try to
>> > get the test case to compile.
>>
>> It doesn't look safe, because 'audit_sock', 'audit_nlk_portid' and 'audit_pid'
>> are updated as a whole and race between audit_receive_msg() and
>> NETLINK_URELEASE.
>
> This is what I expected and why I originally added the mutex lock in the
> callback...  The dumps I got were bare with no wrapper identifying the
> process context or specific error, so I'm at a bit of a loss how to
> solve this (without thinking more about it) other than instinctively
> removing the mutex.

Netlink notifier can safely be converted to blocking one, I will send
a patch.

But I seriously doubt you really need NETLINK_URELEASE here,
it adds nothing but overhead, b/c the netlink notifier is called on
every netlink socket in the system, but for net exit path, that is
relatively a slow path.

Also, kauditd_send_skb() needs audit_cmd_mutex too.

I will send a formal patch.

Thanks.

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Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-11-29 18:00 +0100
  Re: netlink: GPF in sock_sndtimeo Cong Wang <xiyou.wangcong@gmail.com> - 2016-11-30 00:20 +0100
    Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-11-30 06:00 +0100
      Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-12-09 07:10 +0100
        Re: netlink: GPF in sock_sndtimeo Cong Wang <xiyou.wangcong@gmail.com> - 2016-12-09 08:00 +0100
          Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-12-09 12:10 +0100
            Re: netlink: GPF in sock_sndtimeo Cong Wang <xiyou.wangcong@gmail.com> - 2016-12-10 05:20 +0100
              Re: netlink: GPF in sock_sndtimeo Cong Wang <xiyou.wangcong@gmail.com> - 2016-12-10 08:50 +0100
                Re: netlink: GPF in sock_sndtimeo Dmitry Vyukov <dvyukov@google.com> - 2016-12-12 11:10 +0100
                Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-12-13 09:00 +0100
                Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-12-13 09:30 +0100
              Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-12-12 11:10 +0100
                Re: netlink: GPF in sock_sndtimeo Cong Wang <xiyou.wangcong@gmail.com> - 2016-12-13 01:20 +0100
                Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-12-13 12:00 +0100
                Re: netlink: GPF in sock_sndtimeo Cong Wang <xiyou.wangcong@gmail.com> - 2016-12-14 01:40 +0100
                Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-12-14 05:20 +0100
                [RFC PATCH v3] audit: use proper refcount locking on audit_sock Richard Guy Briggs <rgb@redhat.com> - 2016-12-13 16:10 +0100
                Re: [RFC PATCH v3] audit: use proper refcount locking on audit_sock Paul Moore <paul@paul-moore.com> - 2016-12-13 22:00 +0100
                Re: [RFC PATCH v3] audit: use proper refcount locking on audit_sock Cong Wang <xiyou.wangcong@gmail.com> - 2016-12-14 01:20 +0100
                Re: [RFC PATCH v3] audit: use proper refcount locking on audit_sock Richard Guy Briggs <rgb@redhat.com> - 2016-12-14 05:10 +0100
                Re: [RFC PATCH v3] audit: use proper refcount locking on audit_sock Cong Wang <xiyou.wangcong@gmail.com> - 2016-12-14 07:40 +0100
        Re: netlink: GPF in sock_sndtimeo Dmitry Vyukov <dvyukov@google.com> - 2016-12-09 11:50 +0100
          Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-12-09 12:50 +0100
            Re: netlink: GPF in sock_sndtimeo Dmitry Vyukov <dvyukov@google.com> - 2016-12-09 13:00 +0100
              Re: netlink: GPF in sock_sndtimeo Richard Guy Briggs <rgb@redhat.com> - 2016-12-09 13:20 +0100

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