Re: [Patch net] garp: fix a NULL pointer dereference bug

[Eric Dumazet <eric.dumazet@gmail.com>]

On Mon, 2013-03-04 at 11:36 +0800, Cong Wang wrote:
> From: Cong Wang <amwang@redhat.com>
> 
> A NULL-deref bug was reported in:
> https://bugzilla.kernel.org/show_bug.cgi?id=54281
> when deleting a vlan interface:
> 
> # ip link  del em1.57
> BUG: unable to handle kernel NULL pointer dereference at (null)
> IP: [<ffffffffa03c356f>] garp_uninit_applicant+0x2f/0xd0 [garp]
> ...
> 
> This is probably app->pdu is NULL'ed in garp_pdu_rcv()
> in BH, while garp_uninit_applicant() only holds rtnl lock
> which is not enough to prevent this. 
> 
> OTOH, garp_pdu_queue() should ways be called with the spin lock.
> 
> 
> Reported-by: bugs@syam.in
> Cc: bugs@syam.in
> Cc: David Ward <david.ward@ll.mit.edu>
> Cc: Stephen Hemminger <stephen@networkplumber.org>
> Cc: David S. Miller <davem@davemloft.net>
> Signed-off-by: Cong Wang <amwang@redhat.com>
> 
> ---
> diff --git a/net/802/garp.c b/net/802/garp.c
> index 8456f5d..5d9630a 100644
> --- a/net/802/garp.c
> +++ b/net/802/garp.c
> @@ -609,8 +609,12 @@ void garp_uninit_applicant(struct net_device *dev, struct garp_application *appl
>  	/* Delete timer and generate a final TRANSMIT_PDU event to flush out
>  	 * all pending messages before the applicant is gone. */
>  	del_timer_sync(&app->join_timer);
> +
> +	spin_lock_bh(&app->lock);
>  	garp_gid_event(app, GARP_EVENT_TRANSMIT_PDU);
>  	garp_pdu_queue(app);
> +	spin_unlock_bh(&app->lock);
> +
>  	garp_queue_xmit(app);
>  
>  	dev_mc_del(dev, appl->proto.group_address);


Nope this patch doesnt solve the problem

Crash is in :

49 8b 1c c6             mov    (%r14,%rax,8),%rbx 

Thats because r14 (port) is NULL