ip: ip_ra_control() rcu fix

commit 66018506e15b (ip: Router Alert RCU conversion) introduced RCU
lookups to ip_call_ra_chain(). It missed proper deinit phase :
When ip_ra_control() deletes an ip_ra_chain, it should make sure
ip_call_ra_chain() users can not start to use socket during the rcu
grace period. It should also delay the sock_put() after the grace
period, or we risk a premature socket freeing and corruptions, as
raw sockets are not rcu protected yet.

This delay avoids using expensive atomic_inc_not_zero() in
ip_call_ra_chain().

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/ip.h b/include/net/ip.h
index 9982c97f0bdcaf4c09c13cb5f2dc07e2ab2953eb..d52f01180361b159b8c358b26c7a41dfc06f6180 100644 (file)
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -61,7 +61,10 @@ struct ipcm_cookie {
 struct ip_ra_chain {
        struct ip_ra_chain      *next;
        struct sock             *sk;
-       void                    (*destructor)(struct sock *);
+       union {
+               void                    (*destructor)(struct sock *);
+               struct sock             *saved_sk;
+       };
        struct rcu_head         rcu;
 };
 

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 08b9519a24f430a7750d91080f2b8f979f290cbc..47fff528ff39eaaf231fd22338fcff81b9e9b9da 100644 (file)
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -241,9 +241,13 @@ int ip_cmsg_send(struct net *net, struct msghdr *msg, struct ipcm_cookie *ipc)
 struct ip_ra_chain *ip_ra_chain;
 static DEFINE_SPINLOCK(ip_ra_lock);
 
-static void ip_ra_free_rcu(struct rcu_head *head)
+
+static void ip_ra_destroy_rcu(struct rcu_head *head)
 {
-       kfree(container_of(head, struct ip_ra_chain, rcu));
+       struct ip_ra_chain *ra = container_of(head, struct ip_ra_chain, rcu);
+
+       sock_put(ra->saved_sk);
+       kfree(ra);
 }
 
 int ip_ra_control(struct sock *sk, unsigned char on,
@@ -264,13 +268,20 @@ int ip_ra_control(struct sock *sk, unsigned char on,
                                kfree(new_ra);
                                return -EADDRINUSE;
                        }
+                       /* dont let ip_call_ra_chain() use sk again */
+                       ra->sk = NULL;
                        rcu_assign_pointer(*rap, ra->next);
                        spin_unlock_bh(&ip_ra_lock);
 
                        if (ra->destructor)
                                ra->destructor(sk);
-                       sock_put(sk);
-                       call_rcu(&ra->rcu, ip_ra_free_rcu);
+                       /*
+                        * Delay sock_put(sk) and kfree(ra) after one rcu grace
+                        * period. This guarantee ip_call_ra_chain() dont need
+                        * to mess with socket refcounts.
+                        */
+                       ra->saved_sk = sk;
+                       call_rcu(&ra->rcu, ip_ra_destroy_rcu);
                        return 0;
                }
        }