linux-kernel - Re: [PATCH net 1/3] unix/dgram: peek beyond 0-sized skbs

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Message-ID: <1366915736.8964.171.camel@edumazet-glaptop>
Date:	Thu, 25 Apr 2013 11:48:56 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Benjamin Poirier <bpoirier@...e.de>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Pavel Emelyanov <xemul@...allels.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/3] unix/dgram: peek beyond 0-sized skbs

On Thu, 2013-04-25 at 09:47 -0400, Benjamin Poirier wrote:
> "77c1090 net: fix infinite loop in __skb_recv_datagram()" (v3.8) introduced a
> regression:
> After that commit, recv can no longer peek beyond a 0-sized skb in the queue.
> __skb_recv_datagram() instead stops at the first skb with len == 0 and results
> in the system call failing with -EFAULT via skb_copy_datagram_iovec().


if MSG_PEEK is not used, what happens here ?

It doesn't look right to me that we return -EFAULT if skb->len is 0,
EFAULT is reserved to faulting (ie reading/writing at least one byte)

How are we telling the user message had 0 byte, but its not EOF ?



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