Commit 83d51909 authored by Eric Dumazet's avatar Eric Dumazet Committed by Ben Hutchings

macvtap: make sure neighbour code can push ethernet header

[ Upstream commit 2f1d8b9e ]

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: default avatarBrian Rak <brak@vultr.com>
Tested-by: default avatarBrian Rak <brak@vultr.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent 75f9b453
......@@ -667,12 +667,15 @@ 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;
......@@ -731,7 +734,7 @@ 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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