On Wed, May 12, 2010 at 12:28:28PM -0700, Chris Wright wrote: > * Greg KH (greg@xxxxxxxxx) 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). That would require people to update libpci and maybe their scripts as well, which wouldn't be as good. > > > 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. That would be better than having a 'read_file' callback, right? > > 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()? Sure, might as well make it symmetrical :) thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
