[PATCH 5.10.y] batman-adv: retrieve ethhdr after potential skb realloc on RX

[Sven Eckelmann <sven@narfation.org>]

commit 035e1fed892d3d06002a73ff73668f618a514644 upstream.

pskb_may_pull() in batadv_interface_rx() 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.

This was done correctly for the VLAN header but missed for the ethernet
header which is later used for the TT and AP isolation handling.

Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Fixes: c78296665c3d ("batman-adv: Check skb size before using encapsulated ETH+VLAN header")
[ move from mesh- to soft-interface.c ]
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/soft-interface.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index c8c62b0cd54c7..8b4a8e80c0a32 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -454,6 +454,7 @@ void batadv_interface_rx(struct net_device *soft_iface,
 		if (!pskb_may_pull(skb, VLAN_ETH_HLEN))
 			goto dropped;
 
+		ethhdr = eth_hdr(skb);
 		vhdr = skb_vlan_eth_hdr(skb);
 
 		/* drop batman-in-batman packets to prevent loops */
-- 
2.47.3