Re: [PATCH] libmnl: Add filtering support to library as a convienience

[Pablo Neira Ayuso <pablo@netfilter.org>]

Hi Neil,

On Tue, Mar 26, 2013 at 10:20:43AM -0400, Neil Horman wrote:
> Theres been recent discussion about detecting and discarding unwanted netlink
> messages in libmnl, so that we can avoid having applications get spoofed by user
> space processes sending messages with malformed netlink headers.  Commonly
> applications want to be able to only receive messages from the kernel, but
> libmnl currently doesn't offer a mechanism to do that.  This patch adds such a
> mechanism.  It creates a function mnl_socket_recvfrom_filter, that adds an
> extra function pointer parameter which is used to interrogate recieved frames
> and filter them based on a desired criteria.  It also adds a convieninece
> function mnl_recvfrom_filter_user which can be passed as the filter agrument in
> mnl_socket_recvfrom_filter, so as to prevent individual applications from
> re-inventing the wheel over and over again.

I remember that report from Florian. After some discussion, I proposed
this solution:

commit 20e1db19db5d6b9e4e83021595eab0dc8f107bef
Author: Pablo Neira Ayuso <pablo@netfilter.org>
Date:   Thu Aug 23 02:09:11 2012 +0000

    netlink: fix possible spoofing from non-root processes

Basically, it disables netlink-to-netlink communications between
non-root processes (with the exception of NETLINK_USERSOCK), so
non-root processes cannot spoof messages anymore.

Regards.