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

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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.

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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