[PATCH v2 net-next 5/7] tls: Use __sk_dst_get() and dst_dev_rcu() in get_netdev_for_sock().

[Kuniyuki Iwashima <kuniyu@google.com>]

get_netdev_for_sock() is called during setsockopt(),
so not under RCU.

Using sk_dst_get(sk)->dev could trigger UAF.

Let's use __sk_dst_get() and dst_dev_rcu().

Note that the only ->ndo_sk_get_lower_dev() user is
bond_sk_get_lower_dev(), which uses RCU.

Fixes: e8f69799810c ("net/tls: Add generic NIC offload infrastructure")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Sabrina Dubroca <sd@queasysnail.net>
Cc: Ilya Lesokhin <ilyal@mellanox.com>
---
 net/tls/tls_device.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index f672a62a9a52..a82fdcf19969 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -123,17 +123,19 @@ static void tls_device_queue_ctx_destruction(struct tls_context *ctx)
 /* We assume that the socket is already connected */
 static struct net_device *get_netdev_for_sock(struct sock *sk)
 {
-	struct dst_entry *dst = sk_dst_get(sk);
-	struct net_device *netdev = NULL;
+	struct net_device *dev, *lowest_dev = NULL;
+	struct dst_entry *dst;
 
-	if (likely(dst)) {
-		netdev = netdev_sk_get_lowest_dev(dst->dev, sk);
-		dev_hold(netdev);
+	rcu_read_lock();
+	dst = __sk_dst_get(sk);
+	dev = dst ? dst_dev_rcu(dst) : NULL;
+	if (likely(dev)) {
+		lowest_dev = netdev_sk_get_lowest_dev(dev, sk);
+		dev_hold(lowest_dev);
 	}
+	rcu_read_unlock();
 
-	dst_release(dst);
-
-	return netdev;
+	return lowest_dev;
 }
 
 static void destroy_record(struct tls_record_info *record)
-- 
2.51.0.384.g4c02a37b29-goog