Subject: Re: [Patch net] rds: mark bound socket with SOCK_RCU_FREE

From: Sowmini Varadhan <[email-masked]>
Date: Mon, 10 Sep 2018 18:34:12 -0400

On (09/10/18 15:24), Cong Wang wrote:
> 
> When a rds sock is bound, it is inserted into the bind_hash_table
> which is protected by RCU. But when releasing rd sock, after it
> is removed from this hash table, it is freed immediately without
> respecting RCU grace period. This could cause some use-after-free
> as reported by syzbot.
> 

I have no objection to the change itself, but the syzbot failures
are caused for a very simple reason: we need synchronize_net()
in rds_release before we remove the rds_sock from the bind_hash_table.

I already pointed this out in 
  https://www.spinics.net/lists/netdev/msg475074.html

I think the objection to synchronize_net() is that it can cause
perf issues (I'm told that rds_release() has been known to be held
up by other threads in rcu critical sections?) but I personally
dont see any other alternative to this (other than going back
to rwlock, instead of rcu)

--Sowmini