[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>

4 files changed, 90 insertions, 38 deletions

diff --git a/net/sctp/bind_addr.c b/net/sctp/bind_addr.c
index fdb287a9e2e2..7fc369f9035d 100644
--- a/net/sctp/bind_addr.c
+++ b/net/sctp/bind_addr.c
@@ -163,8 +163,10 @@ int sctp_add_bind_addr(struct sctp_bind_addr *bp, union sctp_addr *new,
                 addr->a.v4.sin_port = htons(bp->port);
 
         addr->use_as_src = use_as_src;
+        addr->valid = 1;
 
         INIT_LIST_HEAD(&addr->list);
+        INIT_RCU_HEAD(&addr->rcu);
         list_add_tail(&addr->list, &bp->address_list);
         SCTP_DBG_OBJCNT_INC(addr);
 
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);
                 }
         }
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);
 
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 33354602ae86..a3acf78d06ba 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4057,9 +4057,9 @@ static int sctp_getsockopt_local_addrs_num_old(struct sock *sk, int len,
                                                int __user *optlen)
 {
         sctp_assoc_t id;
+        struct list_head *pos;
         struct sctp_bind_addr *bp;
         struct sctp_association *asoc;
-        struct list_head *pos, *temp;
         struct sctp_sockaddr_entry *addr;
         rwlock_t *addr_lock;
         int cnt = 0;
@@ -4096,15 +4096,19 @@ static int sctp_getsockopt_local_addrs_num_old(struct sock *sk, int len,
                 addr = list_entry(bp->address_list.next,
                                   struct sctp_sockaddr_entry, list);
                 if (sctp_is_any(&addr->a)) {
-                        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 ((PF_INET == sk->sk_family) &&
                                     (AF_INET6 == addr->a.sa.sa_family))
                                         continue;
+
                                 cnt++;
                         }
+                        rcu_read_unlock();
                 } else {
                         cnt = 1;
                 }
@@ -4127,14 +4131,16 @@ static int sctp_copy_laddrs_old(struct sock *sk, __u16 port,
                                         int max_addrs, void *to,
                                         int *bytes_copied)
 {
-        struct list_head *pos, *next;
         struct sctp_sockaddr_entry *addr;
         union sctp_addr temp;
         int cnt = 0;
         int addrlen;
 
-        list_for_each_safe(pos, next, &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 ((PF_INET == sk->sk_family) &&
                     (AF_INET6 == addr->a.sa.sa_family))
                         continue;
@@ -4149,6 +4155,7 @@ static int sctp_copy_laddrs_old(struct sock *sk, __u16 port,
                 cnt ++;
                 if (cnt >= max_addrs) break;
         }
+        rcu_read_unlock();
 
         return cnt;
 }
@@ -4156,14 +4163,16 @@ static int sctp_copy_laddrs_old(struct sock *sk, __u16 port,
 static int sctp_copy_laddrs(struct sock *sk, __u16 port, void *to,
                             size_t space_left, int *bytes_copied)
 {
-        struct list_head *pos, *next;
         struct sctp_sockaddr_entry *addr;
         union sctp_addr temp;
         int cnt = 0;
         int addrlen;
 
-        list_for_each_safe(pos, next, &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 ((PF_INET == sk->sk_family) &&
                     (AF_INET6 == addr->a.sa.sa_family))
                         continue;
@@ -4171,8 +4180,10 @@ static int sctp_copy_laddrs(struct sock *sk, __u16 port, void *to,
                 sctp_get_pf_specific(sk->sk_family)->addr_v4map(sctp_sk(sk),
                                                                 &temp);
                 addrlen = sctp_get_af_specific(temp.sa.sa_family)->sockaddr_len;
-                if (space_left < addrlen)
-                        return -ENOMEM;
+                if (space_left < addrlen) {
+                        cnt =  -ENOMEM;
+                        break;
+                }
                 memcpy(to, &temp, addrlen);
 
                 to += addrlen;
@@ -4180,6 +4191,7 @@ static int sctp_copy_laddrs(struct sock *sk, __u16 port, void *to,
                 space_left -= addrlen;
                 *bytes_copied += addrlen;
         }
+        rcu_read_unlock();
 
         return cnt;
 }