net: sock_copy() fixes

Commit e912b1142be8f1e2c71c71001dc992c6e5eb2ec1
(net: sk_prot_alloc() should not blindly overwrite memory)
took care of not zeroing whole new socket at allocation time.

sock_copy() is another spot where we should be very careful.
We should not set refcnt to a non null value, until
we are sure other fields are correctly setup, or
a lockless reader could catch this socket by mistake,
while not fully (re)initialized.

This patch puts sk_node & sk_refcnt to the very beginning
of struct sock to ease sock_copy() & sk_prot_alloc() job.

We add appropriate smp_wmb() before sk_refcnt initializations
to match our RCU requirements (changes to sock keys should
be committed to memory before sk_refcnt setting)

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

1 files changed, 18 insertions, 2 deletions

diff --git a/net/core/sock.c b/net/core/sock.c
index ba5d211..d9eec15 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -919,13 +919,19 @@ static inline void sock_lock_init(struct sock *sk)
 			af_family_keys + sk->sk_family);
 }
 
+/*
+ * Copy all fields from osk to nsk but nsk->sk_refcnt must not change yet,
+ * even temporarly, because of RCU lookups. sk_node should also be left as is.
+ */
 static void sock_copy(struct sock *nsk, const struct sock *osk)
 {
 #ifdef CONFIG_SECURITY_NETWORK
 	void *sptr = nsk->sk_security;
 #endif
-
-	memcpy(nsk, osk, osk->sk_prot->obj_size);
+	BUILD_BUG_ON(offsetof(struct sock, sk_copy_start) !=
+		     sizeof(osk->sk_node) + sizeof(osk->sk_refcnt));
+	memcpy(&nsk->sk_copy_start, &osk->sk_copy_start,
+	       osk->sk_prot->obj_size - offsetof(struct sock, sk_copy_start));
 #ifdef CONFIG_SECURITY_NETWORK
 	nsk->sk_security = sptr;
 	security_sk_clone(osk, nsk);
@@ -1140,6 +1146,11 @@ struct sock *sk_clone(const struct sock *sk, const gfp_t priority)
 
 		newsk->sk_err	   = 0;
 		newsk->sk_priority = 0;
+		/*
+		 * Before updating sk_refcnt, we must commit prior changes to memory
+		 * (Documentation/RCU/rculist_nulls.txt for details)
+		 */
+		smp_wmb();
 		atomic_set(&newsk->sk_refcnt, 2);
 
 		/*
@@ -1855,6 +1866,11 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 
 	sk->sk_stamp = ktime_set(-1L, 0);
 
+	/*
+	 * Before updating sk_refcnt, we must commit prior changes to memory
+	 * (Documentation/RCU/rculist_nulls.txt for details)
+	 */
+	smp_wmb();
 	atomic_set(&sk->sk_refcnt, 1);
 	atomic_set(&sk->sk_wmem_alloc, 1);
 	atomic_set(&sk->sk_drops, 0);