[PATCH net-next] tun: fix ubuf refcount incorrectly on error path

[wangyunjian]

From: Yunjian Wang <wangyunj...@huawei.com>

After setting callback for ubuf_info of skb, the callback
(vhost_net_zerocopy_callback) will be called to decrease
the refcount when freeing skb. But when an exception occurs
afterwards, the error handling in vhost handle_tx() will
try to decrease the same refcount again. This is wrong and
fix this by clearing ubuf_info when meeting errors.

Fixes: 4477138fa0ae ("tun: properly test for IFF_UP")
Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")

Signed-off-by: Yunjian Wang <wangyunj...@huawei.com>
---
 drivers/net/tun.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2dc1988a8973..3614bb1b6d35 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1861,6 +1861,12 @@ static ssize_t tun_get_user(struct tun_struct *tun, 
struct tun_file *tfile,
        if (unlikely(!(tun->dev->flags & IFF_UP))) {
                err = -EIO;
                rcu_read_unlock();
+               if (zerocopy) {
+                       skb_shinfo(skb)->destructor_arg = NULL;
+                       skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY;
+                       skb_shinfo(skb)->tx_flags &= ~SKBTX_SHARED_FRAG;
+               }
+
                goto drop;
        }
 
@@ -1874,6 +1880,11 @@ static ssize_t tun_get_user(struct tun_struct *tun, 
struct tun_file *tfile,
 
                if (unlikely(headlen > skb_headlen(skb))) {
                        atomic_long_inc(&tun->dev->rx_dropped);
+                       if (zerocopy) {
+                               skb_shinfo(skb)->destructor_arg = NULL;
+                               skb_shinfo(skb)->tx_flags &= 
~SKBTX_DEV_ZEROCOPY;
+                               skb_shinfo(skb)->tx_flags &= ~SKBTX_SHARED_FRAG;
+                       }
                        napi_free_frags(&tfile->napi);
                        rcu_read_unlock();
                        mutex_unlock(&tfile->napi_mutex);
-- 
2.18.1