Re: netlink: GPF in sock_sndtimeo

>> 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&gt; 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. Please let me know what you think about the attached patch?