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

[Andrey Vagin]

On Thu, Dec 22, 2016 at 03:34:15PM -0800, Andrey Vagin wrote:
> 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?

It should be ok, skb_free_datagram() decriments a reference counter

Acked-by: Andrey Vagin <avagin at virtuozzo.com>

> > +		goto out;
> > +	}
> >  
> >  	if (flags & MSG_PEEK)
> >  		sk_peek_offset_fwd(sk, copied);
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