[PATCH net 4/6] batman-adv: dat: acquire ARP hw source only after skb realloc

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

The pskb_may_pull() called by batadv_get_vid() could reallocate the buffer
behind the skb. Variables which were pointing to the old buffer need to be
reassigned to avoid an use-after-free.

Cc: stable@vger.kernel.org
Fixes: b61ec31c8575 ("batman-adv: Snoop DHCPACKs for DAT")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/distributed-arp-table.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index ae39ceaa2e29a..ead02c9e08484 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -1747,6 +1747,7 @@ void batadv_dat_snoop_incoming_dhcp_ack(struct batadv_priv *bat_priv,
 	struct ethhdr *ethhdr;
 	__be32 ip_src, yiaddr;
 	unsigned short vid;
+	int hdr_size_tmp;
 	__be16 proto;
 	u8 *hw_src;
 
@@ -1763,8 +1764,10 @@ void batadv_dat_snoop_incoming_dhcp_ack(struct batadv_priv *bat_priv,
 	if (!batadv_dat_check_dhcp_ack(skb, proto, &ip_src, chaddr, &yiaddr))
 		return;
 
+	hdr_size_tmp = hdr_size;
+	vid = batadv_dat_get_vid(skb, &hdr_size_tmp);
+	ethhdr = (struct ethhdr *)(skb->data + hdr_size);
 	hw_src = ethhdr->h_source;
-	vid = batadv_dat_get_vid(skb, &hdr_size);
 
 	batadv_dat_entry_add(bat_priv, yiaddr, chaddr, vid);
 	batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);
-- 
2.47.3