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>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 01e944a..4da797f 100644 (file)
--- 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);