linux-kernel - [PATCH 3.16.y-ckt 022/165] macvtap: make sure neighbour code can push ethernet header

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Message-Id: <1427292138-7021-23-git-send-email-luis.henriques@canonical.com>
Date:	Wed, 25 Mar 2015 13:59:55 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 022/165] macvtap: make sure neighbour code can push ethernet header

3.16.7-ckt9 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.com>

commit 2f1d8b9e8afa5a833d96afcd23abcb8cdf8d83ab upstream.

Brian reported crashes using IPv6 traffic with macvtap/veth combo.

I tracked the crashes in neigh_hh_output()

-> memcpy(skb->data - HH_DATA_MOD, hh->hh_data, HH_DATA_MOD);

Neighbour code assumes headroom to push Ethernet header is
at least 16 bytes.

It appears macvtap has only 14 bytes available on arches
where NET_IP_ALIGN is 0 (like x86)

Effect is a corruption of 2 bytes right before skb->head,
and possible crashes if accessing non existing memory.

This fix should also increase IPv4 performance, as paranoid code
in ip_finish_output2() wont have to call skb_realloc_headroom()

Reported-by: Brian Rak <brak@...tr.com>
Tested-by: Brian Rak <brak@...tr.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/net/macvtap.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 07c942b6ae01..e8c21f911b6f 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -637,12 +637,15 @@ static void macvtap_skb_to_vnet_hdr(const struct sk_buff *skb,
 	} /* else everything is zero */
 }
 
+/* Neighbour code has some assumptions on HH_DATA_MOD alignment */
+#define MACVTAP_RESERVE HH_DATA_OFF(ETH_HLEN)
+
 /* Get packet from user space buffer */
 static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
 				const struct iovec *iv, unsigned long total_len,
 				size_t count, int noblock)
 {
-	int good_linear = SKB_MAX_HEAD(NET_IP_ALIGN);
+	int good_linear = SKB_MAX_HEAD(MACVTAP_RESERVE);
 	struct sk_buff *skb;
 	struct macvlan_dev *vlan;
 	unsigned long len = total_len;
@@ -701,7 +704,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
 			linear = vnet_hdr.hdr_len;
 	}
 
-	skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, copylen,
+	skb = macvtap_alloc_skb(&q->sk, MACVTAP_RESERVE, copylen,
 				linear, noblock, &err);
 	if (!skb)
 		goto err;
--
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