[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, 39 insertions, 15 deletions

diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index e98579b788b8..7ee120e85913 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -153,6 +153,9 @@ static void sctp_v4_copy_addrlist(struct list_head *addrlist,
                         addr->a.v4.sin_family = AF_INET;
                         addr->a.v4.sin_port = 0;
                         addr->a.v4.sin_addr.s_addr = ifa->ifa_local;
+                        addr->valid = 1;
+                        INIT_LIST_HEAD(&addr->list);
+                        INIT_RCU_HEAD(&addr->rcu);
                         list_add_tail(&addr->list, addrlist);
                 }
         }
@@ -192,16 +195,24 @@ static void sctp_free_local_addr_list(void)
         }
 }
 
+void sctp_local_addr_free(struct rcu_head *head)
+{
+        struct sctp_sockaddr_entry *e = container_of(head,
+                                struct sctp_sockaddr_entry, rcu);
+        kfree(e);
+}
+
 /* Copy the local addresses which are valid for 'scope' into 'bp'.  */
 int sctp_copy_local_addr_list(struct sctp_bind_addr *bp, sctp_scope_t scope,
                               gfp_t gfp, int copy_flags)
 {
         struct sctp_sockaddr_entry *addr;
         int error = 0;
-        struct list_head *pos, *temp;
 
-        list_for_each_safe(pos, temp, &sctp_local_addr_list) {
-                addr = list_entry(pos, struct sctp_sockaddr_entry, list);
+        rcu_read_lock();
+        list_for_each_entry_rcu(addr, &sctp_local_addr_list, list) {
+                if (!addr->valid)
+                        continue;
                 if (sctp_in_scope(&addr->a, scope)) {
                         /* Now that the address is in scope, check to see if
                          * the address type is really supported by the local
@@ -221,6 +232,7 @@ int sctp_copy_local_addr_list(struct sctp_bind_addr *bp, sctp_scope_t scope,
         }
 
 end_copy:
+        rcu_read_unlock();
         return error;
 }
 
@@ -600,13 +612,18 @@ static void sctp_v4_seq_dump_addr(struct seq_file *seq, union sctp_addr *addr)
         seq_printf(seq, "%d.%d.%d.%d ", NIPQUAD(addr->v4.sin_addr));
 }
 
-/* Event handler for inet address addition/deletion events.  */
+/* Event handler for inet 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_inetaddr_event(struct notifier_block *this, unsigned long ev,
                                void *ptr)
 {
         struct in_ifaddr *ifa = (struct in_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:
@@ -615,19 +632,25 @@ static int sctp_inetaddr_event(struct notifier_block *this, unsigned long ev,
                         addr->a.v4.sin_family = AF_INET;
                         addr->a.v4.sin_port = 0;
                         addr->a.v4.sin_addr.s_addr = ifa->ifa_local;
-                        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);
+                spin_lock_bh(&sctp_local_addr_lock);
+                list_for_each_entry_safe(addr, temp,
+                                        &sctp_local_addr_list, list) {
                         if (addr->a.v4.sin_addr.s_addr == ifa->ifa_local) {
-                                list_del(pos);
-                                kfree(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;
         }
 
@@ -1160,6 +1183,7 @@ SCTP_STATIC __init int sctp_init(void)
 
         /* Initialize the local address list. */
         INIT_LIST_HEAD(&sctp_local_addr_list);
+        spin_lock_init(&sctp_local_addr_lock);
         sctp_get_local_addr_list();
 
         /* Register notifier for inet address additions/deletions. */
@@ -1227,6 +1251,9 @@ SCTP_STATIC __exit void sctp_exit(void)
         sctp_v6_del_protocol();
         inet_del_protocol(&sctp_protocol, IPPROTO_SCTP);
 
+        /* Unregister notifier for inet address additions/deletions. */
+        unregister_inetaddr_notifier(&sctp_inetaddr_notifier);
+
         /* Free the local address list.  */
         sctp_free_local_addr_list();
 
@@ -1240,9 +1267,6 @@ SCTP_STATIC __exit void sctp_exit(void)
         inet_unregister_protosw(&sctp_stream_protosw);
         inet_unregister_protosw(&sctp_seqpacket_protosw);
 
-        /* Unregister notifier for inet address additions/deletions. */
-        unregister_inetaddr_notifier(&sctp_inetaddr_notifier);
-
         sctp_sysctl_unregister();
         list_del(&sctp_ipv4_specific.list);