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

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

[Cong Wang]

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);

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

[Cong Wang]

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

I can't reproduce it locally, so please help to test it. I only did
compiling test.

Thanks!

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

[Eric Dumazet]

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

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

[Cong Wang]

On Sun, 2013-03-03 at 21:26 -0800, Eric Dumazet wrote:
> 
> 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
> 
> 
> 

Hmm, but I can't see how it can be NULL, the only place of NULL'ing it
is inside garp_release_port(), right after the piece of code that I
patched.

Thanks!

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

[Eric Dumazet]

On Mon, 2013-03-04 at 17:55 +0800, Cong Wang wrote:
> On Sun, 2013-03-03 at 21:26 -0800, Eric Dumazet wrote:
> > 
> > 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
> > 
> > 
> > 
> 
> Hmm, but I can't see how it can be NULL, the only place of NULL'ing it
> is inside garp_release_port(), right after the piece of code that I
> patched.
> 
> Thanks!
> 

Maybe port is NULL from the beginning.

Try to inject memory allocations error in garp_init_port()