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

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Date:   Fri, 30 Jun 2017 17:19:05 +0200
From:   Mateusz Jurczyk <mjurczyk@...gle.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] netfilter: nfnetlink: Improve input length
 sanitization in nfnetlink_rcv

On Thu, Jun 29, 2017 at 6:22 PM, Pablo Neira Ayuso <pablo@...filter.org> 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.

Sure, I think the condition in nfnetlink_rcv_skb_batch() can be now
safely removed. Feel free to proceed with the mangled patch. Thanks.