[PATCH net-next] tun: fix csum generation for tap devices

[Paolo Abeni]

The commit 34166093639b ("tuntap: use common code for virtio_net_hdr
and skb GSO conversion") replaced the tun code for header manipulation
with the generic helpers. While doing so, it implictly moved the
skb_partial_csum_set() invocation after eth_type_trans(), which
invalidate the current gso start/offset values.
Fix it by moving the helper invocation before the mac pulling.

Fixes: 34166093639 ("tuntap: use common code for virtio_net_hdr and skb GSO 
conversion")
Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
 drivers/net/tun.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 8cc6bf4..4884802 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1254,6 +1254,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, 
struct tun_file *tfile,
                return -EFAULT;
        }
 
+       err = virtio_net_hdr_to_skb(skb, &gso, tun_is_little_endian(tun));
+       if (err) {
+               this_cpu_inc(tun->pcpu_stats->rx_frame_errors);
+               kfree_skb(skb);
+               return -EINVAL;
+       }
+
        switch (tun->flags & TUN_TYPE_MASK) {
        case IFF_TUN:
                if (tun->flags & IFF_NO_PI) {
@@ -1280,13 +1287,6 @@ static ssize_t tun_get_user(struct tun_struct *tun, 
struct tun_file *tfile,
                break;
        }
 
-       err = virtio_net_hdr_to_skb(skb, &gso, tun_is_little_endian(tun));
-       if (err) {
-               this_cpu_inc(tun->pcpu_stats->rx_frame_errors);
-               kfree_skb(skb);
-               return -EINVAL;
-       }
-
        /* copy skb_ubuf_info for callback when skb has no error */
        if (zerocopy) {
                skb_shinfo(skb)->destructor_arg = msg_control;
-- 
1.8.3.1