netlink: add netlink_skb_set_owner_r()

For mmap'ed I/O a netlink specific skb destructor needs to be invoked
after the final kfree_skb() to clean up state. This doesn't work currently
since the skb's ownership is transfered to the receiving socket using
skb_set_owner_r(), which orphans the skb, thereby invoking the destructor
prematurely.

Since netlink doesn't account skbs to the originating socket, there's no
need to orphan the skb. Add a netlink specific skb_set_owner_r() variant
that does not orphan the skb and use a netlink specific destructor to
call sock_rfree().

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 26779c2..58b9025 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -119,6 +119,20 @@ static void netlink_consume_callback(struct netlink_callback *cb)
        kfree(cb);
 }
 
+static void netlink_skb_destructor(struct sk_buff *skb)
+{
+       sock_rfree(skb);
+}
+
+static void netlink_skb_set_owner_r(struct sk_buff *skb, struct sock *sk)
+{
+       WARN_ON(skb->sk != NULL);
+       skb->sk = sk;
+       skb->destructor = netlink_skb_destructor;
+       atomic_add(skb->truesize, &sk->sk_rmem_alloc);
+       sk_mem_charge(sk, skb->truesize);
+}
+
 static void netlink_sock_destruct(struct sock *sk)
 {
        struct netlink_sock *nlk = nlk_sk(sk);
@@ -820,7 +834,7 @@ int netlink_attachskb(struct sock *sk, struct sk_buff *skb,
                }
                return 1;
        }
-       skb_set_owner_r(skb, sk);
+       netlink_skb_set_owner_r(skb, sk);
        return 0;
 }
 
@@ -890,7 +904,7 @@ static int netlink_unicast_kernel(struct sock *sk, struct sk_buff *skb,
        ret = -ECONNREFUSED;
        if (nlk->netlink_rcv != NULL) {
                ret = skb->len;
-               skb_set_owner_r(skb, sk);
+               netlink_skb_set_owner_r(skb, sk);
                NETLINK_CB(skb).sk = ssk;
                nlk->netlink_rcv(skb);
                consume_skb(skb);
@@ -962,7 +976,7 @@ static int netlink_broadcast_deliver(struct sock *sk, struct sk_buff *skb)
 
        if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
            !test_bit(NETLINK_CONGESTED, &nlk->state)) {
-               skb_set_owner_r(skb, sk);
+               netlink_skb_set_owner_r(skb, sk);
                __netlink_sendskb(sk, skb);
                return atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1);
        }