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Message-ID: <4EB84F05.1000704@zytor.com> Date: Mon, 07 Nov 2011 13:35:01 -0800 From: "H. Peter Anvin" <hpa@...or.com> To: Linus Torvalds <torvalds@...ux-foundation.org> CC: Vasiliy Kulikov <segoon@...nwall.com>, Eric Paris <eparis@...isplace.org>, kernel-hardening@...ts.openwall.com, Valdis.Kletnieks@...edu, linux-kernel@...r.kernel.org, Alexey Dobriyan <adobriyan@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-security-module@...r.kernel.org Subject: Re: Re: [PATCH] proc: restrict access to /proc/interrupts On 11/07/2011 01:23 PM, Linus Torvalds wrote: > On Mon, Nov 7, 2011 at 12:47 PM, H. Peter Anvin <hpa@...or.com> wrote: >> >> You didn't really get my point. There are global nodes which are >> dynamic, and more importantly the *set* changes across the system life. >> A global policy option is a lot easier to deal with for the vast >> majority of users who don't need fine grain control. > > I want *one* global policy that the kernel would actually know about: > is the user physically at the machine right now. > > Sadly, I don't think the kernel has any good way to figure that out > automatically. > > Because quite frankly, a lot of the /proc files should be "root or > desktop user". If you control the hardware, you should damn well be > able to see the interrupt counts in order to do bug reports etc > without having to 'sudo' or similar. > > I realize that pam & co could give us this info, or we could just add > a new capability flag, but I think this is something where the kernel > really could just do the RightThing(tm) automatically, and screw the > crazy login managers, odd policies (I really don't believe that adding > magic selinux rules actually improves security all that much, because > it's too painful and too hard to know for any normal user). > > The person in front of the hardware really *is* fundamentally special. > > Right now all the distros do magic things with the audio device > because they know the person in front of the machine is special. But > all those things are ad-hoc per device, and never cover things like > random /proc files etc. > I was going to say "let's just have the login manager add a group to the desktop user's permission set" but then I realized that this would be really bad because of setgid files. Which exposes a real problem with chgrp and setgid files overall. The way setgid works effectively means that any user can become a member of any group that they have at any time been a member of, simply by "stashing" a copy of the group as a setgid file: cp /bin/sh my-saved-group chgrp mygroup my-saved-group chmod g+s my-saved-group This is rather messy, because gids are otherwise a very nice capability mechanism. -hpa
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