From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751558Ab2DPGxQ (ORCPT ); Mon, 16 Apr 2012 02:53:16 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:62978 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751324Ab2DPGxI (ORCPT ); Mon, 16 Apr 2012 02:53:08 -0400 Subject: Re: [PATCH 3/6] macvtap: zerocopy: validate vector length before pinning user pages From: Eric Dumazet To: Jason Wang Cc: netdev@vger.kernel.org, xma@us.ibm.com, davem@davemloft.net, linux-kernel@vger.kernel.org, mst@redhat.com, ebiederm@xmission.com In-Reply-To: <20120416060807.14140.96229.stgit@intel-e5620-16-2.englab.nay.redhat.com> References: <20120416060749.14140.19433.stgit@intel-e5620-16-2.englab.nay.redhat.com> <20120416060807.14140.96229.stgit@intel-e5620-16-2.englab.nay.redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 16 Apr 2012 08:53:03 +0200 Message-ID: <1334559183.28012.45.camel@edumazet-glaptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2012-04-16 at 14:08 +0800, Jason Wang wrote: > Currently we do not validate the vector length before calling > get_user_pages_fast(), host stack would be easily overflowed by > malicious guest driver who give us a descriptor with length greater > than MAX_SKB_FRAGS. Solve this problem by checking the free entries > before trying to pin user pages. > > Signed-off-by: Jason Wang > --- > drivers/net/macvtap.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > index 7cb2684..d197a78 100644 > --- a/drivers/net/macvtap.c > +++ b/drivers/net/macvtap.c > @@ -529,6 +529,8 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from, > } > base = (unsigned long)from->iov_base + offset; > size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT; > + if (i + size >= MAX_SKB_FRAGS) > + return -EFAULT; > num_pages = get_user_pages_fast(base, size, 0, &page[i]); > if ((num_pages != size) || > (num_pages > MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags)) > Hi Jason Why is -EFAULT the right error code ? Also, why not removing the "(num_pages > MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags)" test done few lines after ? Also, if get_user_pages_fast() returns truncated result (size - 1 for example), we apparently dont free the references on pages. The comment applies only on pages that were added in skb frags.