Re: [PATCH 1/1] net: check dev->reg_state before deref of napi netdev_ops

2018-03-12 Thread Josh Elsasser 
On Mon, Mar 12, 2018 at 4:17 PM, Cong Wang  wrote:
> On Sun, Mar 11, 2018 at 12:22 PM, Josh Elsasser  wrote:
>> init_dummy_netdev() leaves its netdev_ops pointer zeroed. This leads
>> to a NULL pointer dereference when sk_busy_loop fires against an iwlwifi
>> wireless adapter and checks napi->dev->netdev_ops->ndo_busy_poll.
>>
>> Avoid this by ensuring that napi->dev is not a dummy device before
>> dereferencing napi dev's netdev_ops, preventing the following panic:
>
> Hmm, how about just checking ->netdev_ops? Checking reg_state looks
> odd, although works.

Fair point. I was trying to differentiate between an unexpected
NULL pointer and a dummy netdev, but I guess it was clever
at the expense of readability.

I'll push up a v2 that just does the obvious.

Re: [PATCH 1/1] net: check dev->reg_state before deref of napi netdev_ops

2018-03-12 Thread Cong Wang 
On Sun, Mar 11, 2018 at 12:22 PM, Josh Elsasser  wrote:
> init_dummy_netdev() leaves its netdev_ops pointer zeroed. This leads
> to a NULL pointer dereference when sk_busy_loop fires against an iwlwifi
> wireless adapter and checks napi->dev->netdev_ops->ndo_busy_poll.
>
> Avoid this by ensuring that napi->dev is not a dummy device before
> dereferencing napi dev's netdev_ops, preventing the following panic:

Hmm, how about just checking ->netdev_ops? Checking reg_state looks
odd, although works.

[PATCH 1/1] net: check dev->reg_state before deref of napi netdev_ops

2018-03-11 Thread Josh Elsasser 
init_dummy_netdev() leaves its netdev_ops pointer zeroed. This leads
to a NULL pointer dereference when sk_busy_loop fires against an iwlwifi
wireless adapter and checks napi->dev->netdev_ops->ndo_busy_poll.

Avoid this by ensuring that napi->dev is not a dummy device before
dereferencing napi dev's netdev_ops, preventing the following panic:

  BUG: unable to handle kernel NULL pointer dereference at 00c8
  IP: [] sk_busy_loop+0x92/0x2f0
  Call Trace:
   [] ? uart_write_room+0x74/0xf0
   [] sock_poll+0x99/0xa0
   [] do_sys_poll+0x2e2/0x520
   [] ? get_page_from_freelist+0x3bc/0xa30
   [] ? update_curr+0x62/0x140
   [] ? __slab_free+0xa1/0x2a0
   [] ? __slab_free+0xa1/0x2a0
   [] ? skb_free_head+0x21/0x30
   [] ? poll_initwait+0x50/0x50
   [] ? kmem_cache_free+0x1c6/0x1e0
   [] ? uart_write+0x124/0x1d0
   [] ? remove_wait_queue+0x4d/0x60
   [] ? __wake_up+0x44/0x50
   [] ? tty_write_unlock+0x31/0x40
   [] ? tty_ldisc_deref+0x16/0x20
   [] ? tty_write+0x1e0/0x2f0
   [] ? process_echoes+0x80/0x80
   [] ? __vfs_write+0x2b/0x130
   [] ? vfs_write+0x15a/0x1a0
   [] SyS_poll+0x75/0x100
   [] entry_SYSCALL_64_fastpath+0x24/0xcf

Commit 79e7fff47b7b ("net: remove support for per driver ndo_busy_poll()")
indirectly fixed this upstream in linux-4.11 by removing the offending
pointer usage. No other users of napi->dev touch its netdev_ops.

Fixes: 060212928670 ("net: add low latency socket poll")
Fixes: ce6aea93f751 ("net: network drivers no longer need to implement 
ndo_busy_poll()") - 4.9.y
Signed-off-by: Josh Elsasser 
---
 net/core/dev.c | 5 -
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 8898618bf341..d0f67d544587 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5042,7 +5042,10 @@ bool sk_busy_loop(struct sock *sk, int nonblock)
goto out;
 
/* Note: ndo_busy_poll method is optional in linux-4.5 */
-   busy_poll = napi->dev->netdev_ops->ndo_busy_poll;
+   if (napi->dev->reg_state != NETREG_DUMMY)
+   busy_poll = napi->dev->netdev_ops->ndo_busy_poll;
+   else
+   busy_poll = NULL;
 
do {
rc = 0;
-- 
2.11.0