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

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 7cb105c103fe..782e38bfc1ee 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -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;
@@ -1034,7 +1039,10 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 
         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);