Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759530Ab3DYS61 (ORCPT ); Thu, 25 Apr 2013 14:58:27 -0400 Received: from mail-da0-f49.google.com ([209.85.210.49]:61944 "EHLO mail-da0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759446Ab3DYS60 (ORCPT ); Thu, 25 Apr 2013 14:58:26 -0400 Message-ID: <1366916303.8964.174.camel@edumazet-glaptop> Subject: Re: [PATCH net 2/3] unix/dgram: fix peeking with an offset larger than data in queue From: Eric Dumazet To: Benjamin Poirier Cc: "David S. Miller" , Eric Dumazet , Pavel Emelyanov , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 25 Apr 2013 11:58:23 -0700 In-Reply-To: <1366897638-21882-2-git-send-email-bpoirier@suse.de> References: <1366897638-21882-1-git-send-email-bpoirier@suse.de> <1366897638-21882-2-git-send-email-bpoirier@suse.de> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4036 Lines: 117 On Thu, 2013-04-25 at 09:47 -0400, Benjamin Poirier wrote: > Currently, peeking on a unix datagram socket with an offset larger than len of > the data in the sk receive queue returns immediately with bogus data. That's > because *off is not reset between each skb_queue_walk(). > > This patch fixes this so that the behavior is the same as peeking with no > offset on an empty queue: the caller blocks. > > Signed-off-by: Benjamin Poirier > --- > net/core/datagram.c | 25 +++++++++++++++---------- > 1 file changed, 15 insertions(+), 10 deletions(-) > > diff --git a/net/core/datagram.c b/net/core/datagram.c > index 02398ae..6c502b5 100644 > --- a/net/core/datagram.c > +++ b/net/core/datagram.c > @@ -78,9 +78,10 @@ static int receiver_wake_function(wait_queue_t *wait, unsigned int mode, int syn > return autoremove_wake_function(wait, mode, sync, key); > } > /* > - * Wait for a packet.. > + * Wait for the last received packet to be different from skb > */ > -static int wait_for_packet(struct sock *sk, int *err, long *timeo_p) > +static int wait_for_more_packets(struct sock *sk, int *err, long *timeo_p, > + struct sk_buff *skb) const struct sk_buff *skb > { > int error; > DEFINE_WAIT_FUNC(wait, receiver_wake_function); > @@ -92,7 +93,7 @@ static int wait_for_packet(struct sock *sk, int *err, long *timeo_p) > if (error) > goto out_err; > > - if (!skb_queue_empty(&sk->sk_receive_queue)) > + if ((struct sk_buff *)sk->sk_receive_queue.prev != skb) Why is the cast needed ? > goto out; > > /* Socket shut down? */ > @@ -131,9 +132,9 @@ out_noerr: > * __skb_recv_datagram - Receive a datagram skbuff > * @sk: socket > * @flags: MSG_ flags > - * @off: an offset in bytes to peek skb from. Returns an offset > - * within an skb where data actually starts > * @peeked: returns non-zero if this packet has been seen before > + * @_off: an offset in bytes to peek skb from. Returns an offset > + * within an skb where data actually starts > * @err: error code returned > * > * Get a datagram skbuff, understands the peeking, nonblocking wakeups > @@ -159,9 +160,9 @@ out_noerr: > * the standard around please. > */ > struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags, > - int *peeked, int *off, int *err) > + int *peeked, int *_off, int *err) > { > - struct sk_buff *skb; > + struct sk_buff *skb, *last; > long timeo; > /* > * Caller is allowed not to check sk->sk_err before skb_recv_datagram() > @@ -182,13 +183,16 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags, > */ > unsigned long cpu_flags; > struct sk_buff_head *queue = &sk->sk_receive_queue; > + int off = *_off; > > spin_lock_irqsave(&queue->lock, cpu_flags); > + last = (struct sk_buff *)queue; This could be done before spin_lock > skb_queue_walk(queue, skb) { > + last = skb; > *peeked = skb->peeked; > if (flags & MSG_PEEK) { > - if (*off >= skb->len && (skb->len || *off)) { > - *off -= skb->len; > + if (off >= skb->len && (skb->len || off)) { > + off -= skb->len; > continue; > } > skb->peeked = 1; > @@ -197,6 +201,7 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags, > __skb_unlink(skb, queue); > > spin_unlock_irqrestore(&queue->lock, cpu_flags); > + *_off = off; > return skb; > } > spin_unlock_irqrestore(&queue->lock, cpu_flags); > @@ -206,7 +211,7 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags, > if (!timeo) > goto no_packet; > > - } while (!wait_for_packet(sk, err, &timeo)); > + } while (!wait_for_more_packets(sk, err, &timeo, last)); > > return NULL; > Other than that, patch seems fine. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/