Re: [PATCH] [RFC] Make it easier to harden /proc/

[Richard Weinberger <richard@nod.at>]

Am Mittwoch 16 März 2011, 22:04:52 schrieb Alexey Dobriyan:
> On Wed, Mar 16, 2011 at 09:52:49PM +0100, Richard Weinberger wrote:
> > 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?
> 
> It only covers /proc/sys/net/

Exactly.

> > > I had expected that any dangerous sysctl would not be visible in
> > > an unpriviledge container anyway.
> > 
> > No way.
> 
> No way what exactly?

Dangerous sysctls are not protected at all.
E.g. A jailed root can use /proc/sysrq-trigger.

> 
> > That's why it's currently a very good idea to mount /proc/ read-only into
> > a container.