Re: netlink: GPF in sock_sndtimeo
On Fri, Dec 9, 2016 at 3:01 AM, Richard Guy Briggs <rgb(a)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(a)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.