From c37ccc0d4e2a4ee52f1a40cff1be0049f2104bba Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sat, 1 Nov 2008 21:19:18 -0700 Subject: [PATCH] udp: add a missing smp_wmb() in udp_lib_get_port() Corey Minyard spotted a missing memory barrier in udp_lib_get_port() We need to make sure a reader cannot read the new 'sk->sk_next' value and previous value of 'sk->sk_hash'. Or else, an item could be deleted from a chain, and inserted into another chain. If new chain was empty before the move, 'next' pointer is NULL, and lockless reader can not detect it missed following items in original chain. This patch is temporary, since we expect an upcoming patch to introduce another way of handling the problem. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/udp.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index bcb5def2b09..7e4d9c87115 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -189,6 +189,11 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum, inet_sk(sk)->num = snum; sk->sk_hash = snum; if (sk_unhashed(sk)) { + /* + * We need that previous write to sk->sk_hash committed + * before write to sk->next done in following add_node() variant + */ + smp_wmb(); sk_add_node_rcu(sk, &hslot->head); sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1); } -- 2.11.4.GIT