netlink: use kfree_rcu() in netlink_release()

On some suspend/resume operations involving wimax device, we have
noticed some intermittent memory corruptions in netlink code.

Stéphane Marchesin tracked this corruption in netlink_update_listeners()
and suggested a patch.

It appears netlink_release() should use kfree_rcu() instead of kfree()
for the listeners structure as it may be used by other cpus using RCU
protection.

netlink_release() must set to NULL the listeners pointer when
it is about to be freed.

Also have to protect netlink_update_listeners() and
netlink_has_listeners() if listeners is NULL.

Add a nl_deref_protected() lockdep helper to properly document which
locks protects us.

Reported-by: Jonathan Kliegman <kliegs@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Stéphane Marchesin <marcheu@google.com>
Cc: Sam Leffler <sleffler@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 4 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 01e944a017a4..4da797fa5ec5 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -138,6 +138,8 @@ static int netlink_dump(struct sock *sk);
 static DEFINE_RWLOCK(nl_table_lock);
 static atomic_t nl_table_users = ATOMIC_INIT(0);
 
+#define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
+
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static inline u32 netlink_group_mask(u32 group)
@@ -345,6 +347,11 @@ netlink_update_listeners(struct sock *sk)
         struct hlist_node *node;
         unsigned long mask;
         unsigned int i;
+        struct listeners *listeners;
+
+        listeners = nl_deref_protected(tbl->listeners);
+        if (!listeners)
+                return;
 
         for (i = 0; i < NLGRPLONGS(tbl->groups); i++) {
                 mask = 0;
@@ -352,7 +359,7 @@ netlink_update_listeners(struct sock *sk)
                         if (i < NLGRPLONGS(nlk_sk(sk)->ngroups))
                                 mask |= nlk_sk(sk)->groups[i];
                 }
-                tbl->listeners->masks[i] = mask;
+                listeners->masks[i] = mask;
         }
         /* this function is only called with the netlink table "grabbed", which
          * makes sure updates are visible before bind or setsockopt return. */
@@ -536,7 +543,11 @@ static int netlink_release(struct socket *sock)
         if (netlink_is_kernel(sk)) {
                 BUG_ON(nl_table[sk->sk_protocol].registered == 0);
                 if (--nl_table[sk->sk_protocol].registered == 0) {
-                        kfree(nl_table[sk->sk_protocol].listeners);
+                        struct listeners *old;
+
+                        old = nl_deref_protected(nl_table[sk->sk_protocol].listeners);
+                        RCU_INIT_POINTER(nl_table[sk->sk_protocol].listeners, NULL);
+                        kfree_rcu(old, rcu);
                         nl_table[sk->sk_protocol].module = NULL;
                         nl_table[sk->sk_protocol].bind = NULL;
                         nl_table[sk->sk_protocol].flags = 0;
@@ -982,7 +993,7 @@ int netlink_has_listeners(struct sock *sk, unsigned int group)
         rcu_read_lock();
         listeners = rcu_dereference(nl_table[sk->sk_protocol].listeners);
 
-        if (group - 1 < nl_table[sk->sk_protocol].groups)
+        if (listeners && group - 1 < nl_table[sk->sk_protocol].groups)
                 res = test_bit(group - 1, listeners->masks);
 
         rcu_read_unlock();
@@ -1625,7 +1636,7 @@ int __netlink_change_ngroups(struct sock *sk, unsigned int groups)
                 new = kzalloc(sizeof(*new) + NLGRPSZ(groups), GFP_ATOMIC);
                 if (!new)
                         return -ENOMEM;
-                old = rcu_dereference_protected(tbl->listeners, 1);
+                old = nl_deref_protected(tbl->listeners);
                 memcpy(new->masks, old->masks, NLGRPSZ(tbl->groups));
                 rcu_assign_pointer(tbl->listeners, new);