[PATCH 3.2 196/221] macvtap: limit head length of skb allocated

Ben Hutchings
2015-05-05T02:31:41Z

From: Jason Wang <jasowang@redhat.com>

commit 16a3fa28630331e28208872fa5341ce210b901c7 upstream.

We currently use hdr_len as a hint of head length which is advertised by
guest. But when guest advertise a very big value, it can lead to an 64K+
allocating of kmalloc() which has a very high possibility of failure when host
memory is fragmented or under heavy stress. The huge hdr_len also reduce the
effect of zerocopy or even disable if a gso skb is linearized in guest.

To solves those issues, this patch introduces an upper limit (PAGE_SIZE) of the
head, which guarantees an order 0 allocation each time.

Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/net/macvtap.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -672,6 +672,7 @@ static ssize_t macvtap_get_user(struct m
const struct iovec *iv, unsigned long total_len,
size_t count, int noblock)
{
+ int good_linear = SKB_MAX_HEAD(NET_IP_ALIGN);
struct sk_buff *skb;
struct macvlan_dev *vlan;
unsigned long len = total_len;
@@ -714,6 +715,8 @@ static ssize_t macvtap_get_user(struct m

if (m && m->msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
copylen = vnet_hdr.hdr_len ? vnet_hdr.hdr_len : GOODCOPY_LEN;
+ if (copylen > good_linear)
+ copylen = good_linear;
linear = copylen;
if (iov_pages(iv, vnet_hdr_len + copylen, count)
<= MAX_SKB_FRAGS)
@@ -722,7 +725,10 @@ static ssize_t macvtap_get_user(struct m

if (!zerocopy) {
copylen = len;
- linear = vnet_hdr.hdr_len;
+ if (vnet_hdr.hdr_len > good_linear)
+ linear = good_linear;
+ else
+ linear = vnet_hdr.hdr_len;
}

skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, copylen,