[Devel] [PATCH rh7 v2] netlink: Don't manipulate @sk_peek_off if data fetching failed

[Konstantin Khorenko]

Andrey, are you going to send your patch to mainstream?
(Kirill's patch is based on your patch, AFAIK)

commit 523b88d0b87acbc7af9ae1677e993ed20f55dc5e
Author: Andrey Vagin <avagin at openvz.org>
Date:   Fri Jun 17 14:27:30 2016 +0400

     netlink: allow to set peeking offset for sockets


--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 03/21/2017 10:10 PM, Andrey Vagin wrote:
> Acked-by: Andrey Vagin <avagin at virtuozzo.com>
>
> On Fri, Dec 23, 2016 at 10:19:01AM +0300, Cyrill Gorcunov wrote:
>> On Fri, Dec 23, 2016 at 09:59:28AM +0300, Cyrill Gorcunov wrote:
>>> On Thu, Dec 22, 2016 at 04:45:10PM -0800, Andrey Vagin wrote:
>>>>
>>>> Actually, this patch breaks the old behaviour even when MSG_PEEK isn't set.
>>>>
>>>> I was thinking a bit more and I don't understand why it is a problem. If
>>>> we can't fill a buffer, an error will be returned and a user will be able
>>>> to set peek_offset to get these data again.
>>>
>>> A user doesn't have to set peek again, without the patch the internal state
>>> of sk is context-dependant, which is broken design. Take a look on unix
>>> sockets code, they DON'T modify offset if something earlier failed for
>>> exactly same reason.
>>
>> Another option -- set offset only iff data copying passed.
>> ---
>> From: Cyrill Gorcunov <gorcunov at openvz.org>
>> Subject: [PATCH rh7 v2] netlink: Don't manipulate @sk_peek_off if data fetching failed
>>
>> When skb_copy_datagram_iovec called to fetch queued data
>> it may fail with EFAULT and if MSG_PEEK set by a caller
>> the position get advanced even if data hasn't been read.
>> So we might loose data bits here on subsequent recvmsg
>> calls. Instead lets exit early with error.
>>
>> In sake of https://jira.sw.ru/browse/PSBM-57921
>>
>> CC: Andrey Vagin <avagin at openvz.org>
>> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
>> ---
>>  net/netlink/af_netlink.c |   11 ++++++-----
>>  1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> Index: linux-pcs7.git/net/netlink/af_netlink.c
>> ===================================================================
>> --- linux-pcs7.git.orig/net/netlink/af_netlink.c
>> +++ linux-pcs7.git/net/netlink/af_netlink.c
>> @@ -2473,11 +2473,12 @@ static int netlink_recvmsg(struct kiocb
>>
>>  	skb_reset_transport_header(data_skb);
>>  	err = skb_copy_datagram_iovec(data_skb, skip, msg->msg_iov, copied);
>> -
>> -	if (flags & MSG_PEEK)
>> -		sk_peek_offset_fwd(sk, copied);
>> -	else
>> -		sk_peek_offset_bwd(sk, skb->len);
>> +	if (!err) {
>> +		if (flags & MSG_PEEK)
>> +			sk_peek_offset_fwd(sk, copied);
>> +		else
>> +			sk_peek_offset_bwd(sk, skb->len);
>> +	}
>>
>>  	if (msg->msg_name) {
>>  		struct sockaddr_nl *addr = (struct sockaddr_nl *)msg->msg_name;
> _______________________________________________
> Devel mailing list
> Devel at openvz.org
> https://lists.openvz.org/mailman/listinfo/devel
> .
>