Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 96f8d9ec authored by Jason Wang's avatar Jason Wang Committed by David S. Miller
Browse files

tuntap: 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 6115c11f

drivers/net/tun.c

+9 −1
Original line number Diff line number Diff line
@@ -981,6 +981,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, 
	struct sk_buff *skb;

	size_t len = total_len, align = NET_SKB_PAD, linear;

	struct virtio_net_hdr gso = { 0 };

	int good_linear;

	int offset = 0;

	int copylen;

	bool zerocopy = false;
@@ -1021,12 +1022,16 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, 
			return -EINVAL;

	}



	good_linear = SKB_MAX_HEAD(align);



	if (msg_control) {

		/* There are 256 bytes to be copied in skb, so there is

		 * enough room for skb expand head in case it is used.

		 * The rest of the buffer is mapped from userspace.

		 */

		copylen = gso.hdr_len ? gso.hdr_len : GOODCOPY_LEN;

		if (copylen > good_linear)

			copylen = good_linear;

		linear = copylen;

		if (iov_pages(iv, offset + copylen, count) <= MAX_SKB_FRAGS)

			zerocopy = true;
@@ -1034,6 +1039,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, 


	if (!zerocopy) {

		copylen = len;

		if (gso.hdr_len > good_linear)

			linear = good_linear;

		else

			linear = gso.hdr_len;

	}