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: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 9dccb1edfd2a..dc76670c2f2a 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -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)
@@ -678,7 +681,10 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *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,