netdev - Re: Kernel 4.1.12 crash

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Date:	Wed, 2 Dec 2015 18:23:35 +0100
From:	Guillaume Nault <g.nault@...halink.fr>
To:	Andrew <nitr0@...i.kr.ua>
Cc:	Alexander Duyck <alexander.duyck@...il.com>,
	netdev@...r.kernel.org, Simon Farnsworth <simon@...nz.org.uk>
Subject: Re: Kernel 4.1.12 crash

On Mon, Nov 30, 2015 at 09:42:08PM +0100, Guillaume Nault wrote:
> On Mon, Nov 30, 2015 at 04:03:37PM +0100, Guillaume Nault wrote:
> > Yes, it most likely was introduced by 287f3a943fef ("pppoe: Use
> > workqueue to die properly when a PADT is received"). I still have to
> > figure out why.
> 
> I confirm the bug comes from this commit.
> 
> It happens if pppoe_connect() reinitialises po->proto.pppoe.padt_work
> after pppoe_disc_rcv() has added it to the system's work queue, and
> before that work got scheduled. Then when scheduling occurs, the worker
> thread tries to run a corrupted structure and crashes.
> 
> I'm going to work on a patch.

You can try the following. It's not yet a proper fix as there are still
a few things that bug me in pppoe_connect().

---
diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
index 5e0b432..865b74d 100644
--- a/drivers/net/ppp/pppoe.c
+++ b/drivers/net/ppp/pppoe.c
@@ -568,6 +568,9 @@ static int pppoe_create(struct net *net, struct socket *sock, int kern)
 	sk->sk_family		= PF_PPPOX;
 	sk->sk_protocol		= PX_PROTO_OE;
 
+	INIT_WORK(&pppox_sk(sk)->proto.pppoe.padt_work,
+		  pppoe_unbind_sock_work);
+
 	return 0;
 }
 
@@ -632,8 +635,6 @@ static int pppoe_connect(struct socket *sock, struct sockaddr *uservaddr,
 
 	lock_sock(sk);
 
-	INIT_WORK(&po->proto.pppoe.padt_work, pppoe_unbind_sock_work);
-
 	error = -EINVAL;
 	if (sp->sa_protocol != PX_PROTO_OE)
 		goto end;
@@ -663,8 +664,6 @@ static int pppoe_connect(struct socket *sock, struct sockaddr *uservaddr,
 			po->pppoe_dev = NULL;
 		}
 
-		memset(sk_pppox(po) + 1, 0,
-		       sizeof(struct pppox_sock) - sizeof(struct sock));
 		sk->sk_state = PPPOX_NONE;
 	}
 
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