From a83e4448958bd0542012648411b868c5a4d57b33 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 27 Feb 2015 18:35:35 -0800 Subject: [PATCH] macvtap: make sure neighbour code can push ethernet header [ Upstream commit 2f1d8b9e8afa5a833d96afcd23abcb8cdf8d83ab ] 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 Tested-by: Brian Rak Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- 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 2d255ba911d5..8fc46fcaee54 100644 --- a/drivers/net/macvtap.c +++ b/drivers/net/macvtap.c @@ -658,12 +658,15 @@ static unsigned long iov_pages(const struct iovec *iv, int offset, return pages; } +/* 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; @@ -722,7 +725,7 @@ 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; -- 2.34.1