netdev - [PATCH 2/3] batman-adv: Force mac header to start of data on xmit

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Message-Id: <20190201111412.13807-3-sw@simonwunderlich.de>
Date:   Fri,  1 Feb 2019 12:14:11 +0100
From:   Simon Wunderlich <sw@...onwunderlich.de>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, b.a.t.m.a.n@...ts.open-mesh.org,
        Sven Eckelmann <sven@...fation.org>,
        Simon Wunderlich <sw@...onwunderlich.de>
Subject: [PATCH 2/3] batman-adv: Force mac header to start of data on xmit

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

The caller of ndo_start_xmit may not already have called
skb_reset_mac_header. The returned value of skb_mac_header/eth_hdr
therefore can be in the wrong position and even outside the current skbuff.
This for example happens when the user binds to the device using a
PF_PACKET-SOCK_RAW with enabled qdisc-bypass:

  int opt = 4;
  setsockopt(sock, SOL_PACKET, PACKET_QDISC_BYPASS, &opt, sizeof(opt));

Since eth_hdr is used all over the codebase, the batadv_interface_tx
function must always take care of resetting it.

Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Reported-by: syzbot+9d7405c7faa390e60b4e@...kaller.appspotmail.com
Reported-by: syzbot+7d20bc3f1ddddc0f9079@...kaller.appspotmail.com
Signed-off-by: Sven Eckelmann <sven@...fation.org>
Signed-off-by: Simon Wunderlich <sw@...onwunderlich.de>
---
 net/batman-adv/soft-interface.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index 5db5a0a4c959..b85ca809e509 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -221,6 +221,8 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 
 	netif_trans_update(soft_iface);
 	vid = batadv_get_vid(skb, 0);
+
+	skb_reset_mac_header(skb);
 	ethhdr = eth_hdr(skb);
 
 	switch (ntohs(ethhdr->h_proto)) {
-- 
2.11.0