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    SubjectRe: [ANNOUNCE][PATCH] New fs to control access to system resources
    On Tue, Jan 15, 2002 at 05:01:11PM +0100, Olaf Dietsche wrote:
    > this is a new file system to control access to system resources.
    > Currently it controls access to inet_bind() with ports < 1024 only.

    Just some minor notes from reading the source and docs:

    - It somewhat collides with the Linux Security Module project
    ( LSM is AFAIK very likely to be included
    into kernel somewhere in the 2.5 timeframe, so I don't think your
    accessfs in its current form will be included into 2.5. Also I don't
    think it will be included into 2.4 some time, as it is rather
    intrusive. This doesn't mean that I think your work is bogus, but
    you should be warned that you will most likely have to maintain it
    as a separate patch at least until you port it to LSM (which
    probably will not be possible at least in the first phase of LSM -
    read the discussions on "restrictive vs. authoritative hooks" in the
    LSM mailinglist archives).
    - CAP_NET_BIND_SERVICE is ignored completely. IMHO a process with this
    capability should still be able to override the accessfs
    permissions, otherwise enabling accessfs will break every setup
    where CAP_NET_BIND_SERVICE is already used to give non-root
    processes access to low ports. At least this should be mentioned in
    the docs (and entry!), as it means that you can't mix
    the accessfs and the capability approach on a machine (e.g. if one
    wants to migrate the services on the machine one for one). It also
    breaks any network daemons that already use CAP_NET_BIND_SERVICE
    internally (don't know of an example, but maybe there are some out
    - chown()ing a port to a uid provides this uid also with the ability
    to pass on access privileges to others via chmod(). It could be
    argued if it is more sensible to restrict changing privileges to
    root (maybe CAP_NET_ADMIN is more appropriate?).

    And some wishlist items:

    - It would be nice if there were a way to distinguish between TCP and
    UDP ports.
    - IPv6 support would be nice. This raises the question what will
    happen if a process has the privileges to bind a particular port
    with IPv6 but not with IPv4 (IPv6 listeners take IPv4 connections
    also). Is there any value in distinguishing IPv6 and IPv4 at all,
    in particular if IPv6 gets into more widespread use in the future?
    - Restricting access to certain high ports would be valuable. For
    example many SQL server use those ports, and it would be nice if one
    could prevent ordinary user processes from taking over their ports
    in case the SQL daemon gets restarted or the like.

    At least accessfs is a nice and expandable idea. Keep up the work :-)

    Andreas Ferber - dev/consulting GmbH - Bielefeld, FRG
    +49 521 1365800 - -
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