From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v2 net 2/2] macvtap: correctly linearize skb when zerocopy is used Date: Wed, 10 Jul 2013 09:15:43 +0300 Message-ID: <20130710061542.GE19759@redhat.com> References: <1373435008-19407-1-git-send-email-jasowang@redhat.com> <1373435008-19407-2-git-send-email-jasowang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <1373435008-19407-2-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Jul 10, 2013 at 01:43:28PM +0800, Jason Wang wrote: > Userspace may produce vectors greater than MAX_SKB_FRAGS. When we try to > linearize parts of the skb to let the rest of iov to be fit in > the frags, we need count copylen into linear when calling macvtap_alloc_skb() > instead of partly counting it into data_len. Since this breaks > zerocopy_sg_from_iovec() since its inner counter assumes nr_frags should > be zero at beginning. This cause nr_frags to be increased wrongly without > setting the correct frags. > > This bug were introduced from b92946e2919134ebe2a4083e4302236295ea2a73 > (macvtap: zerocopy: validate vectors before building skb). > > Cc: Michael S. Tsirkin > Signed-off-by: Jason Wang Acked-by: Michael S. Tsirkin > --- > - This patch is needed for stable. > - Changes from v1: introduce a local variable to track linear size. > --- > drivers/net/macvtap.c | 8 ++++++-- > 1 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > index b6dd6a7..502d948 100644 > --- a/drivers/net/macvtap.c > +++ b/drivers/net/macvtap.c > @@ -647,6 +647,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m, > int vnet_hdr_len = 0; > int copylen = 0; > bool zerocopy = false; > + size_t linear; > > if (q->flags & IFF_VNET_HDR) { > vnet_hdr_len = q->vnet_hdr_sz; > @@ -701,11 +702,14 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m, > copylen = vnet_hdr.hdr_len; > if (!copylen) > copylen = GOODCOPY_LEN; > - } else > + linear = copylen; > + } else { > copylen = len; > + linear = vnet_hdr.hdr_len; > + } > > skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, copylen, > - vnet_hdr.hdr_len, noblock, &err); > + linear, noblock, &err); > if (!skb) > goto err; > > -- > 1.7.1