From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH 3/6] macvtap: zerocopy: validate vector length before pinning user pages Date: Mon, 16 Apr 2012 16:21:35 +0800 Message-ID: <4F8BD68F.7070708@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> <1334559183.28012.45.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, xma@us.ibm.com, davem@davemloft.net, linux-kernel@vger.kernel.org, mst@redhat.com, ebiederm@xmission.com To: Eric Dumazet Return-path: In-Reply-To: <1334559183.28012.45.camel@edumazet-glaptop> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Hi: On 04/16/2012 02:53 PM, Eric Dumazet wrote: > 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 ? E2BIG or is there any error code you prefer? > > Also, why not removing the "(num_pages> MAX_SKB_FRAGS - > skb_shinfo(skb)->nr_frags)" test done few lines after ? Yes, it can be removed. > > Also, if get_user_pages_fast() returns truncated result (size - 1 for > example), we apparently dont free the references on pages. It's a bug of this patch, thanks. > The comment applies only on pages that were added in skb frags. > >