linux-kernel - [PATCH 4.4 51/93] batman-adv: Fix ICMP RR ethernet access after skb

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Date:   Thu, 19 Mar 2020 13:59:55 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sven Eckelmann <sven@...fation.org>,
        Marek Lindner <mareklindner@...mailbox.ch>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 51/93] batman-adv: Fix ICMP RR ethernet access after skb_linearize

From: Sven Eckelmann <sven@...fation.org>

commit 3b55e4422087f9f7b241031d758a0c65584e4297 upstream.

The skb_linearize may reallocate the skb. This makes the calculated pointer
for ethhdr invalid. But it the pointer is used later to fill in the RR
field of the batadv_icmp_packet_rr packet.

Instead re-evaluate eth_hdr after the skb_linearize+skb_cow to fix the
pointer and avoid the invalid read.

Fixes: da6b8c20a5b8 ("batman-adv: generalize batman-adv icmp packet handling")
Signed-off-by: Sven Eckelmann <sven@...fation.org>
Signed-off-by: Marek Lindner <mareklindner@...mailbox.ch>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/batman-adv/routing.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -359,6 +359,7 @@ int batadv_recv_icmp_packet(struct sk_bu
 		if (skb_cow(skb, ETH_HLEN) < 0)
 			goto out;
 
+		ethhdr = eth_hdr(skb);
 		icmph = (struct batadv_icmp_header *)skb->data;
 		icmp_packet_rr = (struct batadv_icmp_packet_rr *)icmph;
 		if (icmp_packet_rr->rr_cur >= BATADV_RR_LEN)