From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757193Ab0ELT2o (ORCPT ); Wed, 12 May 2010 15:28:44 -0400 Received: from sous-sol.org ([216.99.217.87]:48486 "EHLO sequoia.sous-sol.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754511Ab0ELT2m (ORCPT ); Wed, 12 May 2010 15:28:42 -0400 Date: Wed, 12 May 2010 12:28:28 -0700 From: Chris Wright To: Greg KH Cc: Chris Wright , jbarnes@virtuousgeek.org, matthew@wil.cx, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, ddutile@redhat.com, alex.williamson@redhat.com Subject: Re: [RFC PATCH] sysfs: bin_attr permission checking Message-ID: <20100512192828.GX28034@sequoia.sous-sol.org> References: <20100512184713.GV28034@sequoia.sous-sol.org> <20100512191336.GA30678@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100512191336.GA30678@kroah.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Greg KH (greg@kroah.com) wrote: > On Wed, May 12, 2010 at 11:47:13AM -0700, Chris Wright wrote: > > The PCI config space bin_attr read handler has a hardcoded CAP_SYS_ADMIN > > check to verify privileges before allowing a user to read device > > dependent config space. This is meant to protect from an unprivileged > > user potentially locking up the box. > > > > When assigning a PCI device directly to a guest with libvirt and KVM, the > > sysfs config space file is chown'd to the user that the KVM guest will > > run as. The guest needs to have full access to the device's config > > space since it's responsible for driving the device. However, despite > > being the owner of the sysfs file, the CAP_SYS_ADMIN check will not > > allow read access beyond the config header. > > > > This patch adds a new bin_attr->read_file() callback which adds a struct > > file to the normal argument list. This allows an implementation such as > > PCI config space bin_attr read_file handler to check both inode > > permission as well as privileges to determine whether to allow > > privileged actions through the handler. > > Ick, this is all because we like showing different information if the > user is "privileged or not" :( yup > Turns out, that this probably isn't the best user api to implement, > remind me never to do that again... Yeah, it's challenging to deal with. Alternative here is a new config sysfs entry that doesn't have this 'feature'. (I looked into trying to allow manageing the internal capable() check externally, not so pretty). > > This is just RFC, although I've tested that it does allow the chown + > > read to work as expected. Any other ideas of how to handle this are > > welcome. > > Can we just pass in the 'file' for all users of the bin files instead of > the dentry? The dentry doesn't currently go beyond sysfs/bin.c. So, yes, I pushed 'file' through to last level in bin.c before ->read(), and can certinaly just push through to ->read() as well. > You can always get the dentry from the file (as your patch > showes), and there isn't that many users of this interface. I'd really > rather not have two different types of callbacks here. Absolutely, this is just RFC (i.e. quicker to compile and test). What about write()? thanks, -chris