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

[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@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
---
 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

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

[Al Viro]

On Sat, Apr 29, 2017 at 10:38:48AM +0800, Ding Tianhong wrote:
> 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.

The bug is real, but I would suggest a simpler fix:
                if (__skb_checksum_complete(skb))
                        return -EINVAL;
leaving the rest as-is.

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

[Ding Tianhong]

On 2017/4/29 10:46, Al Viro wrote:
> On Sat, Apr 29, 2017 at 10:38:48AM +0800, Ding Tianhong wrote:
>> 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.
> 
> The bug is real, but I would suggest a simpler fix:
>                 if (__skb_checksum_complete(skb))
>                         return -EINVAL;
> leaving the rest as-is.
> 
Looks good, if so, we don't need the csum_error any more,

-		if (csum_fold(csum))
+
+		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;

DO you agree this way? :)

Thanks
Ding

> .
> 

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

[Al Viro]

On Sat, Apr 29, 2017 at 05:37:38PM +0800, Ding Tianhong wrote:

> Looks good, if so, we don't need the csum_error any more,

Acked-by: Al Viro <viro@zeniv.linux.org.uk>

Dave, I could put that through my tree, but I think it would be better off
in net.git; either way, it needs to go into mainline before -final...

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

[David Miller]

From: Al Viro <viro@ZenIV.linux.org.uk>
Date: Sat, 29 Apr 2017 21:48:23 +0100

> On Sat, Apr 29, 2017 at 05:37:38PM +0800, Ding Tianhong wrote:
> 
>> Looks good, if so, we don't need the csum_error any more,
> 
> Acked-by: Al Viro <viro@zeniv.linux.org.uk>
> 
> Dave, I could put that through my tree, but I think it would be better off
> in net.git; either way, it needs to go into mainline before -final...

Please just send it directly to Linus, thanks.