Re: [PATCH net 1/5] vxlan: re-fetch eth header after route_shortcircuit()

Before route_shortcircuit(), the eth header pointer is cached from eth_hdr(skb).

Inside route_shortcircuit(), pskb_may_pull() can be called, which may
reallocate skb->head.

In this case, returning to vxlan_xmit() leaves the cached eth pointer pointing to
freed memory, leading to a use-after-free when dereferencing eth->h_dest.

Fix this by updating eth = eth_hdr(skb) after calling route_shortcircuit().

Fixes: ae8840825605 ("VXLAN: Allow L2 redirection with L3 switching")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
  drivers/net/vxlan/vxlan_core.c | 1 +
  1 file changed, 1 insertion(+)

diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index 67c367cc566233e809b0f70e0d939dd1c1ac0d9f..9060a1259ac283d4db4b7a854ce74203496e9313 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c

@@ -2796,6 +2796,7 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev)
  	    (ntohs(eth->h_proto) == ETH_P_IP ||
  	     ntohs(eth->h_proto) == ETH_P_IPV6)) {
  		did_rsc = route_shortcircuit(dev, skb);
+		eth = eth_hdr(skb);
  		if (did_rsc)
  			f = vxlan_find_mac_tx(vxlan, eth->h_dest, vni);
  	}