[SCTP]: Add RCU synchronization around sctp_localaddr_list

sctp_localaddr_list is modified dynamically via NETDEV_UP
and NETDEV_DOWN events, but there is not synchronization
between writer (even handler) and readers.  As a result,
the readers can access an entry that has been freed and
crash the sytem.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Sridhar Samdurala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 24 insertions, 10 deletions

diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index f8aa23dda1c1..e12fa0a91da4 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -77,13 +77,18 @@
 
 #include <asm/uaccess.h>
 
-/* Event handler for inet6 address addition/deletion events.  */
+/* Event handler for inet6 address addition/deletion events.
+ * The sctp_local_addr_list needs to be protocted by a spin lock since
+ * multiple notifiers (say IPv4 and IPv6) may be running at the same
+ * time and thus corrupt the list.
+ * The reader side is protected with RCU.
+ */
 static int sctp_inet6addr_event(struct notifier_block *this, unsigned long ev,
                                 void *ptr)
 {
         struct inet6_ifaddr *ifa = (struct inet6_ifaddr *)ptr;
-        struct sctp_sockaddr_entry *addr;
-        struct list_head *pos, *temp;
+        struct sctp_sockaddr_entry *addr = NULL;
+        struct sctp_sockaddr_entry *temp;
 
         switch (ev) {
         case NETDEV_UP:
@@ -94,19 +99,26 @@ static int sctp_inet6addr_event(struct notifier_block *this, unsigned long ev,
                         memcpy(&addr->a.v6.sin6_addr, &ifa->addr,
                                  sizeof(struct in6_addr));
                         addr->a.v6.sin6_scope_id = ifa->idev->dev->ifindex;
-                        list_add_tail(&addr->list, &sctp_local_addr_list);
+                        addr->valid = 1;
+                        spin_lock_bh(&sctp_local_addr_lock);
+                        list_add_tail_rcu(&addr->list, &sctp_local_addr_list);
+                        spin_unlock_bh(&sctp_local_addr_lock);
                 }
                 break;
         case NETDEV_DOWN:
-                list_for_each_safe(pos, temp, &sctp_local_addr_list) {
-                        addr = list_entry(pos, struct sctp_sockaddr_entry, list);
-                        if (ipv6_addr_equal(&addr->a.v6.sin6_addr, &ifa->addr)) {
-                                list_del(pos);
-                                kfree(addr);
+                spin_lock_bh(&sctp_local_addr_lock);
+                list_for_each_entry_safe(addr, temp,
+                                        &sctp_local_addr_list, list) {
+                        if (ipv6_addr_equal(&addr->a.v6.sin6_addr,
+                                             &ifa->addr)) {
+                                addr->valid = 0;
+                                list_del_rcu(&addr->list);
                                 break;
                         }
                 }
-
+                spin_unlock_bh(&sctp_local_addr_lock);
+                if (addr && !addr->valid)
+                        call_rcu(&addr->rcu, sctp_local_addr_free);
                 break;
         }
 
@@ -367,7 +379,9 @@ static void sctp_v6_copy_addrlist(struct list_head *addrlist,
                         addr->a.v6.sin6_port = 0;
                         addr->a.v6.sin6_addr = ifp->addr;
                         addr->a.v6.sin6_scope_id = dev->ifindex;
+                        addr->valid = 1;
                         INIT_LIST_HEAD(&addr->list);
+                        INIT_RCU_HEAD(&addr->rcu);
                         list_add_tail(&addr->list, addrlist);
                 }
         }