netdev - Re: Crash with SO_REUSEPORT and ef456144da8ef507c8cf504284b6042e9201a05c

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Date:	Tue, 19 Jan 2016 13:11:31 -0500
From:	Craig Gallek <kraig@...gle.com>
To:	Marc Dionne <marc.c.dionne@...il.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: Crash with SO_REUSEPORT and ef456144da8ef507c8cf504284b6042e9201a05c

On Tue, Jan 19, 2016 at 12:08 PM, Marc Dionne <marc.c.dionne@...il.com> wrote:
> On Tue, Jan 19, 2016 at 12:31 PM, Craig Gallek <kraig@...gle.com> wrote:
>>
>> I need to think about how to handle setsockopt-after-bind condition a
>> bit more, but the NULL pointer dereference is obviously wrong.  Do you
>> have a way to easily reproduce this?  I've only managed to get it to
>> happen once so far...
>
> The attached code reliably triggers the crash for me.

I think the patch below will address this issue (sorry in advance if
gmail screws up the whitespace...).  I'll send it for formal review
once I finish testing it.

Craig

diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
index 1df98c557440..004cb2c974ac 100644
--- a/net/core/sock_reuseport.c
+++ b/net/core/sock_reuseport.c
@@ -97,6 +97,11 @@ int reuseport_add_sock(struct sock *sk, const
struct sock *sk2)
 {
  struct sock_reuseport *reuse;

+  if (!rcu_access_pointer(sk2->sk_reuseport_cb)) {
+   int err = reuseport_alloc(sk2);
+   if (err) return err;
+  }
+
  spin_lock_bh(&reuseport_lock);
  reuse = rcu_dereference_protected(sk2->sk_reuseport_cb,
   lockdep_is_held(&reuseport_lock)),