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

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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 @@ int llc_rcv(struct sk_buff *skb, struct net_device *dev,
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)