Patch "packet: only test po->has_vnet_hdr once in packet_snd" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

    packet: only test po->has_vnet_hdr once in packet_snd

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
packet-only-test-po-has_vnet_hdr-once-in-packet_snd.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Willem de Bruijn <[email protected]>
Date: Tue, 26 Sep 2017 12:20:17 -0400
Subject: packet: only test po->has_vnet_hdr once in packet_snd

From: Willem de Bruijn <[email protected]>

[ Upstream commit da7c9561015e93d10fe6aab73e9288e0d09d65a6 ]

Packet socket option po->has_vnet_hdr can be updated concurrently with other operations if no ring is attached.

Do not test the option twice in packet_snd, as the value may change in between calls. A race on setsockopt disable may cause a packet > mtu to be sent without having GSO options set.

---
 net/packet/af_packet.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -1713,7 +1713,7 @@ static int fanout_add(struct sock *sk, u
 	}
 	spin_unlock(&po->bind_lock);
 
-	if (err && !refcount_read(&match->sk_ref)) {
+	if (err && !atomic_read(&match->sk_ref)) {
 		list_del(&match->list);
 		kfree(match);
 	}

@@ -2838,6 +2838,7 @@ static int packet_snd(struct socket *soc
 	struct virtio_net_hdr vnet_hdr = { 0 };
 	int offset = 0;
 	struct packet_sock *po = pkt_sk(sk);
+	bool has_vnet_hdr = false;
 	int hlen, tlen, linear;
 	int extra_len = 0;
 

@@ -2881,6 +2882,7 @@ static int packet_snd(struct socket *soc
 		err = packet_snd_vnet_parse(msg, &len, &vnet_hdr);
 		if (err)
 			goto out_unlock;
+		has_vnet_hdr = true;
 	}
 
 	if (unlikely(sock_flag(sk, SOCK_NOFCS))) {

@@ -2941,7 +2943,7 @@ static int packet_snd(struct socket *soc
 
 	packet_pick_tx_queue(dev, skb);
 
-	if (po->has_vnet_hdr) {
+	if (has_vnet_hdr) {
 		err = packet_snd_vnet_gso(skb, &vnet_hdr);
 		if (err)
 			goto out_free;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/packet-in-packet_do_bind-test-fanout-with-bind_lock-held.patch queue-4.9/packet-only-test-po-has_vnet_hdr-once-in-packet_snd.patch queue-4.9/packet-hold-bind-lock-when-rebinding-to-fanout-hook.patch