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

[Andrey Vagin]

On Thu, Dec 22, 2016 at 06:41:42PM +0300, Cyrill Gorcunov wrote:
> 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 |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> 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
> @@ -2473,6 +2473,10 @@ 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 (err) {
> +		skb_free_datagram(sk, skb);

hmmm, why do we need to call skb_free_datagram?
> +		goto out;
> +	}
>  
>  	if (flags & MSG_PEEK)
>  		sk_peek_offset_fwd(sk, copied);