tun: Optimise handling of bogus gso->hdr_len

As all current versions of virtio_net generate a value for the
header length that's too small, we should optimise this so that
we don't copy it twice.  This can be done by ensuring that it is
at least as large as the place where we'll write the checksum.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 3f0cdc14be82a5e6353920c836962bd11c397cd1..8d82511aa1bca6c134d8828d6962082160502bba 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -565,6 +565,10 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
                if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
                        return -EFAULT;
 
+               if ((gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
+                   gso.csum_start + gso.csum_offset + 2 > gso.hdr_len)
+                       gso.hdr_len = gso.csum_start + gso.csum_offset + 2;
+
                if (gso.hdr_len > len)
                        return -EINVAL;
                offset += sizeof(pi);