iov_iter: don't revert iov buffer if csum error

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")
Cc: stable@vger.kernel.org # v4.11
Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 7 insertions, 6 deletions

diff --git a/net/core/datagram.c b/net/core/datagram.c
index f4947e737f34..d797baa69e43 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -760,7 +760,7 @@ int skb_copy_and_csum_datagram_msg(struct sk_buff *skb,
 
         if (msg_data_left(msg) < chunk) {
                 if (__skb_checksum_complete(skb))
-                        goto csum_error;
+                        return -EINVAL;
                 if (skb_copy_datagram_msg(skb, hlen, msg, chunk))
                         goto fault;
         } else {
@@ -768,15 +768,16 @@ 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))
-                        goto csum_error;
+
+                if (csum_fold(csum)) {
+                        iov_iter_revert(&msg->msg_iter, chunk);
+                        return -EINVAL;
+                }
+
                 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;
 }