linux-kernel - Re: [netfilter-core] [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink

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Date:   Mon, 17 Jul 2017 13:31:17 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Mateusz Jurczyk <mjurczyk@...gle.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        coreteam@...filter.org, netfilter-devel@...r.kernel.org,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [netfilter-core] [PATCH v2] netfilter: nfnetlink: Improve input
 length sanitization in nfnetlink_rcv

On Thu, Jun 29, 2017 at 06:22:40PM +0200, Pablo Neira Ayuso wrote:
> On Tue, Jun 27, 2017 at 07:05:27PM +0200, Pablo Neira Ayuso wrote:
> > On Tue, Jun 27, 2017 at 05:58:25PM +0200, Pablo Neira Ayuso wrote:
> > > On Wed, Jun 07, 2017 at 03:50:38PM +0200, Mateusz Jurczyk wrote:
> > > > Verify that the length of the socket buffer is sufficient to cover the
> > > > nlmsghdr structure before accessing the nlh->nlmsg_len field for further
> > > > input sanitization. If the client only supplies 1-3 bytes of data in
> > > > sk_buff, then nlh->nlmsg_len remains partially uninitialized and
> > > > contains leftover memory from the corresponding kernel allocation.
> > > > Operating on such data may result in indeterminate evaluation of the
> > > > nlmsg_len < NLMSG_HDRLEN expression.
> > > > 
> > > > The bug was discovered by a runtime instrumentation designed to detect
> > > > use of uninitialized memory in the kernel. The patch prevents this and
> > > > other similar tools (e.g. KMSAN) from flagging this behavior in the future.
> > > 
> > > Applied, thanks.
> > 
> > Wait, I keeping this back after closer look.
> > 
> > I think we have to remove this:
> > 
> >         if (nlh->nlmsg_len < NLMSG_HDRLEN || <---
> >             skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
> >                 return;
> > 
> > in nfnetlink_rcv_skb_batch()
> > 
> > now that we make this unfront check from nfnetlink_rcv().
> 
> BTW, I can just mangle your patch here to delete such line to speed up
> things. See the mangled patch that is attached to this email.

OK, I have applied this to the nf tree.

Thanks!