[PATCH 3.12 15/83] tuntap: limit head length of skb allocated

Greg Kroah-Hartman
2013-12-06T21:52:24Z

From: Jason Wang <jasowang@redhat.com>

[ Upstream commit 96f8d9ecf227638c89f98ccdcdd50b569891976c ]

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/tun.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -981,6 +981,7 @@ static ssize_t tun_get_user(struct tun_s
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_s
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;
@@ -1034,7 +1039,10 @@ static ssize_t tun_get_user(struct tun_s

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

skb = tun_alloc_skb(tfile, align, copylen, linear, noblock);