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Commit 16a3fa28 authored by Jason Wang's avatar Jason Wang Committed by David S. Miller
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macvtap: limit head length of skb allocated 



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: default avatarJason Wang <jasowang@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 96f8d9ec

drivers/net/macvtap.c

+7 −1
Original line number Diff line number Diff line
@@ -628,6 +628,7 @@ 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);

	struct sk_buff *skb;

	struct macvlan_dev *vlan;

	unsigned long len = total_len;
@@ -670,6 +671,8 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *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)
@@ -678,6 +681,9 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m, 


	if (!zerocopy) {

		copylen = len;

		if (vnet_hdr.hdr_len > good_linear)

			linear = good_linear;

		else

			linear = vnet_hdr.hdr_len;

	}