Re: [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv

From	Mateusz Jurczyk <mjurczyk@google.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv
Date	2017-06-30 17:20 +0200
Message-ID	<tY5S9-77y-13@gated-at.bofh.it> (permalink)
References	<tPJc7-7aN-27@gated-at.bofh.it> <tPJF7-7mI-5@gated-at.bofh.it> <tX14e-2Bz-5@gated-at.bofh.it> <tX29X-3yC-1@gated-at.bofh.it> <tXKum-1qg-17@gated-at.bofh.it>
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On Thu, Jun 29, 2017 at 6:22 PM, Pablo Neira Ayuso <pablo@netfilter.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.

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Re: [PATCH v2] netfilter: nfnetlink: Improve input length  sanitization in nfnetlink_rcv Pablo Neira Ayuso <pablo@netfilter.org> - 2017-06-27 18:00 +0200
  Re: [PATCH v2] netfilter: nfnetlink: Improve input length  sanitization in nfnetlink_rcv Pablo Neira Ayuso <pablo@netfilter.org> - 2017-06-27 19:10 +0200
    Re: [PATCH v2] netfilter: nfnetlink: Improve input length  sanitization in nfnetlink_rcv Pablo Neira Ayuso <pablo@netfilter.org> - 2017-06-29 18:30 +0200
      Re: [PATCH v2] netfilter: nfnetlink: Improve input length  sanitization in nfnetlink_rcv Mateusz Jurczyk <mjurczyk@google.com> - 2017-06-30 17:20 +0200

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