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llc: Fix races between llc2 handler use and (un)registration 

When registering the handlers, any state they rely on must be
completely initialised first.  When unregistering, we must wait until
they are definitely no longer running.  llc_rcv() must also avoid
reading the handler pointers again after checking for NULL.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Ben Hutchings 2012-08-13 02:50:55 +00:00 committed by David S. Miller
parent f4f8720feb
commit aadf31de16
2 changed files with 18 additions and 5 deletions
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21
net/llc/llc_input.c
View File

@ -42,6 +42,7 @@ static void (*llc_type_handlers[2])(struct llc_sap *sap,
void llc_add_pack(int type, void (*handler)(struct llc_sap *sap,
struct sk_buff *skb))
{
smp_wmb(); /* ensure initialisation is complete before it's called */
if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
llc_type_handlers[type - 1] = handler;
}
@ -50,11 +51,19 @@ void llc_remove_pack(int type)
{
if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
llc_type_handlers[type - 1] = NULL;
synchronize_net();
}
void llc_set_station_handler(void (*handler)(struct sk_buff *skb))
{
/* Ensure initialisation is complete before it's called */
if (handler)
smp_wmb();
llc_station_handler = handler;
if (!handler)
synchronize_net();
}
/**
@ -150,6 +159,8 @@ int llc_rcv(struct sk_buff *skb, struct net_device *dev,
int dest;
int (*rcv)(struct sk_buff *, struct net_device *,
struct packet_type *, struct net_device *);
void (*sta_handler)(struct sk_buff *skb);
void (*sap_handler)(struct llc_sap *sap, struct sk_buff *skb);
if (!net_eq(dev_net(dev), &init_net))
goto drop;
@ -182,7 +193,8 @@ int llc_rcv(struct sk_buff *skb, struct net_device *dev,
*/
rcv = rcu_dereference(sap->rcv_func);
dest = llc_pdu_type(skb);
if (unlikely(!dest || !llc_type_handlers[dest - 1])) {
sap_handler = dest ? ACCESS_ONCE(llc_type_handlers[dest - 1]) : NULL;
if (unlikely(!sap_handler)) {
if (rcv)
rcv(skb, dev, pt, orig_dev);
else
@ -193,7 +205,7 @@ int llc_rcv(struct sk_buff *skb, struct net_device *dev,
if (cskb)
rcv(cskb, dev, pt, orig_dev);
}
llc_type_handlers[dest - 1](sap, skb);
sap_handler(sap, skb);
}
llc_sap_put(sap);
out:
@ -202,9 +214,10 @@ drop:
kfree_skb(skb);
goto out;
handle_station:
if (!llc_station_handler)
sta_handler = ACCESS_ONCE(llc_station_handler);
if (!sta_handler)
goto drop;
llc_station_handler(skb);
sta_handler(skb);
goto out;
}

2
net/llc/llc_station.c
View File

@ -696,9 +696,9 @@ void __init llc_station_init(void)
(unsigned long)&llc_main_station);
llc_main_station.ack_timer.expires = jiffies +
sysctl_llc_station_ack_timeout;
llc_set_station_handler(llc_station_rcv);
llc_main_station.maximum_retry = 1;
llc_main_station.state = LLC_STATION_STATE_UP;
llc_set_station_handler(llc_station_rcv);
}
void llc_station_exit(void)