[PATCH v2] iov_iter: don't revert iov buffer if csum error

[Ding Tianhong]

The patch 327868212381 (make skb_copy_datagram_msg() et.al. preserve
->msg_iter on error) will revert the iov buffer if copy to iter
failed, but it didn't copy any datagram if the skb_checksum_complete
error, so no need to revert any data at this place.

v2: Sabrina notice that return -EFAULT when checksum error is not correct
    here, it would confuse the caller about the return value, so fix it.

Fixes: 327868212381 ("make skb_copy_datagram_msg() et.al. preserve->msg_iter on error")
Signed-off-by: Ding Tianhong <dingtianhong@xxxxxxxxxx>
Signed-off-by: Wei Yongjun <weiyongjun1@xxxxxxxxxx>
---
 net/core/datagram.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/core/datagram.c b/net/core/datagram.c
index f4947e7..0e6a9a9 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -768,14 +768,17 @@ int skb_copy_and_csum_datagram_msg(struct sk_buff *skb,
 		if (skb_copy_and_csum_datagram(skb, hlen, &msg->msg_iter,
 					       chunk, &csum))
 			goto fault;
-		if (csum_fold(csum))
+
+		if (csum_fold(csum)) {
+			iov_iter_revert(&msg->msg_iter, chunk);
 			goto csum_error;
+		}
+
 		if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE))
 			netdev_rx_csum_fault(skb->dev);
 	}
 	return 0;
 csum_error:
-	iov_iter_revert(&msg->msg_iter, chunk);
 	return -EINVAL;
 fault:
 	return -EFAULT;
-- 
1.8.3.1