[PATCH NET v4 5/7] vrf: use skb_expand_head in vrf_finish_output

[Vasily Averin]

Unlike skb_realloc_headroom, new helper skb_expand_head
does not allocate a new skb if possible.

Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
---
v4: fixes null pointer dereference reported by Julian Wiedmann,
replace skb->dev by dev = skb_dst(skb)->dev
vrf_finish_output() is only called from vrf_output(),
it set skb->dev to skb_dst(skb)->dev and calls POSTROUTING netfilter
hooks, where output device should not be changed.
---
 drivers/net/vrf.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index 2b1b944..168d4ef 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -857,30 +857,24 @@ static int vrf_finish_output(struct net *net, struct sock *sk, struct sk_buff *s
 	unsigned int hh_len = LL_RESERVED_SPACE(dev);
 	struct neighbour *neigh;
 	bool is_v6gw = false;
-	int ret = -EINVAL;
 
 	nf_reset_ct(skb);
 
 	/* Be paranoid, rather than too clever. */
 	if (unlikely(skb_headroom(skb) < hh_len && dev->header_ops)) {
-		struct sk_buff *skb2;
-
-		skb2 = skb_realloc_headroom(skb, LL_RESERVED_SPACE(dev));
-		if (!skb2) {
-			ret = -ENOMEM;
-			goto err;
+		skb = skb_expand_head(skb, hh_len);
+		if (!skb) {
+			dev->stats.tx_errors++;
+			return -ENOMEM;
 		}
-		if (skb->sk)
-			skb_set_owner_w(skb2, skb->sk);
-
-		consume_skb(skb);
-		skb = skb2;
 	}
 
 	rcu_read_lock_bh();
 
 	neigh = ip_neigh_for_gw(rt, skb, &is_v6gw);
 	if (!IS_ERR(neigh)) {
+		int ret;
+
 		sock_confirm_neigh(skb, neigh);
 		/* if crossing protocols, can not use the cached header */
 		ret = neigh_output(neigh, skb, is_v6gw);
@@ -889,9 +883,8 @@ static int vrf_finish_output(struct net *net, struct sock *sk, struct sk_buff *s
 	}
 
 	rcu_read_unlock_bh();
-err:
-	vrf_tx_error(skb->dev, skb);
-	return ret;
+	vrf_tx_error(dev, skb);
+	return -EINVAL;
 }
 
 static int vrf_output(struct net *net, struct sock *sk, struct sk_buff *skb)
-- 
1.8.3.1