[B.A.T.M.A.N.] [PATCHv4 maint] batman-adv: fix potential kernel paging error for unicast transmissions

["Linus Lüssing" <linus.luessing@web.de>]

batadv_send_skb_prepare_unicast(_4addr) might reallocate the skb's
data. If it does then our ethhdr pointer is not valid anymore in
batadv_send_skb_unicast(), resulting in a kernel paging error.

Fixing this by refetching the ethhdr pointer after the potential
reallocation.

Introduced by b46c60b9e1ee7a1909c542413a85875a750955d6
("batman-adv: improve unicast packet (re)routing")

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
---
Changes v4:
* "s/Introduced-by:/Introduced by/" to make checkpatch happy

 send.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/send.c b/send.c
index b0a3d76..50df184 100644
--- a/send.c
+++ b/send.c
@@ -281,6 +281,10 @@ static int batadv_send_skb_unicast(struct batadv_priv *bat_priv,
 		goto out;
 	}
 
+	/* skb->data might have been reallocated by
+	 * batadv_send_skb_prepare_unicast*
+	 */
+	ethhdr = eth_hdr(skb);
 	unicast_packet = (struct batadv_unicast_packet *)skb->data;
 
 	/* inform the destination node that we are still missing a correct route
-- 
1.7.10.4