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>

diff --git a/net/llc/llc_input.c b/net/llc/llc_input.c
index e32cab44ea959d8f49781d46580b4204afb7e3cb..dd3e83328ad544d3183233da61fa40289975de51 100644 (file)
--- a/net/llc/llc_input.c
+++ b/net/llc/llc_input.c
@@ -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;
 }
 

diff --git a/net/llc/llc_station.c b/net/llc/llc_station.c
index bba5184fafd7966ec26fadd4a51163f07a62c0d7..b2f2bac2c2a2397b5fd6f6b79659996270b96377 100644 (file)
--- a/net/llc/llc_station.c
+++ b/net/llc/llc_station.c
@@ -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)