>-----Original Message----- >From: Toshiaki Makita [mailto:makita.toshiaki@xxxxxxxxxxxxx] >Sent: Thursday, November 06, 2014 4:07 PM >To: 박수현; Stephen Hemminger; David S. Miller >Cc: bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux- >kernel@xxxxxxxxxxxxxxx >Subject: Re: [PATCH] bridge: missing null bridge device check causing null >pointer dereference (bugfix) > >On 2014/11/06 15:26, Su-Hyun Park wrote: >> the bridge device can be null if the bridge is being deleted while >> processing the packet, which causes the null pointer dereference in >switch statement. > >How can this happen?? >It is guarded by rcu. >netdev_rx_handler_unregister() ensures rx_handler_data is non NULL. > The RCU protect rx_handler_data, not the bridge member port. It can be NULL according to below code. static inline struct net_bridge_port *br_port_get_rcu(const struct net_device *dev) { struct net_bridge_port *port = rcu_dereference(dev->rx_handler_data); return br_port_exists(dev) ? port : NULL; } The crash happens at the below switch statement in br_handle_frame, where p is NULL. switch (p->state) >> >> crash dump snippet: >> >> <1>BUG: unable to handle kernel NULL pointer dereference at >> 0000000000000021 >> <1>IP: [<ffffffff814179f6>] br_handle_frame+0xe6/0x270 >> >> <0>Code: 4c 0f 44 f0 89 f8 66 33 15 32 52 24 00 66 33 05 29 52 24 00 >> 09 c2 89 >> f0 66 33 05 22 52 24 00 80 e4 f0 66 09 c2 0f 84 eb 00 00 00 <41> 0f b6 >> 46 21 3c 02 74 61 3c 03 74 1d 48 89 df e8 d5 bc f0 ff >> --- >> net/bridge/br_input.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c index >> 6fd5522..7e899ca 100644 >> --- a/net/bridge/br_input.c >> +++ b/net/bridge/br_input.c >> @@ -176,6 +176,8 @@ rx_handler_result_t br_handle_frame(struct sk_buff >**pskb) >> return RX_HANDLER_CONSUMED; >> >> p = br_port_get_rcu(skb->dev); >> + if (!p) >> + goto drop; >> >> if (unlikely(is_link_local_ether_addr(dest))) { >> u16 fwd_mask = p->br->group_fwd_mask_required; >> >
