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    SubjectRe: [PATCH] [RFC] Make it easier to harden /proc/
    Date
    Am Mittwoch 16 März 2011, 22:17:39 schrieb Eric W. Biederman:
    > Richard Weinberger <richard@nod.at> writes:
    >
    > 2> Am Mittwoch 16 März 2011, 21:45:45 schrieb Arnd Bergmann:
    > >> On Wednesday 16 March 2011 21:08:16 Richard Weinberger wrote:
    > >> > Am Mittwoch 16 März 2011, 20:55:49 schrieb Kees Cook:
    > >> > > On Wed, Mar 16, 2011 at 08:31:47PM +0100, Richard Weinberger wrote:
    > >> > > > When containers like LXC are used a unprivileged and jailed
    > >> > > > root user can still write to critical files in /proc/.
    > >> > > > E.g: /proc/sys/kernel/{sysrq, panic, panic_on_oops, ... }
    > >> > > >
    > >> > > > This new restricted attribute makes it possible to protect such
    > >> > > > files. When restricted is set to true root needs CAP_SYS_ADMIN
    > >> > > > to into the file.
    > >> > >
    > >> > > I was thinking about this too. I'd prefer more fine-grained control
    > >> > > in this area, since some sysctl entries aren't strictly controlled
    > >> > > by CAP_SYS_ADMIN (e.g. mmap_min_addr is already checking
    > >> > > CAP_SYS_RAWIO).
    > >> > >
    > >> > > How about this instead?
    > >> >
    > >> > Good Idea.
    > >> > May we should also consider a per-directory restriction.
    > >> > Every file in /proc/sys/{kernel/, vm/, fs/, dev/} needs a protection.
    > >> > It would be much easier to set the protection on the parent directory
    > >> > instead of protecting file by file...
    > >>
    > >> How does this interact with the per-namespace sysctls that Eric
    > >> Biederman added a few years ago?
    > >
    > > Do you mean CONFIG_{UTS, UPC, USER, NET,}_NS?
    > >
    > >> I had expected that any dangerous sysctl would not be visible in
    > >> an unpriviledge container anyway.
    > >
    > > No way.
    > > That's why it's currently a very good idea to mount /proc/ read-only
    > > into a container.
    >
    > However it is in the architecture. The problem is that the user
    > namespace is not finished. Once finished even root with all caps in a
    > container will have no more permissions than the unprivileged user that
    > created the user namespace.
    >
    > Essentially the change is to make permissions checks become a comparison
    > of the tuple (user_ns, uid) instead of just comparisons by uid. If we
    > want to fix permission problems with proc and containers please let's
    > focus on the completing the user namespace.

    Ok. What's the current status, where can I help?

    > Eric

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