Re: netlink: GPF in sock_sndtimeo

On Fri, Dec 9, 2016 at 3:01 AM, Richard Guy Briggs <rgb(a)redhat.com&gt; 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&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.