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    SubjectRe: [PATCH] Security/sysfs: Enable security xattrs to be set on sysfs files, directories, and symlinks.
    On Thu, 2009-07-09 at 10:52 -0700, Greg KH wrote:
    > On Thu, Jul 09, 2009 at 01:13:33PM -0400, David P. Quigley wrote:
    > > The issue is that there really aren't any LSM hooks to accommodate that.
    > > I have a few LSM hooks for the Labeled NFS work which could be used for
    > > this but it still requires us to store the full xattr value somewhere
    > > and referencing it in the sysfs_dirent structure.
    > A void pointer would handle that properly, right?

    A void pointer would suffice if we wanted to store the opaque blob. My
    argument is that storing that blob is too heavy weight memory wise.

    > > The issue here is that there are two ways of presenting security
    > > information. The first is through the xattr interface which represents
    > > the security information as an opaque blob which the LSM turns into an
    > > internal representation. The second which is left over from the early
    > > days is the secid which I equate to a file handle. The problem I see
    > > is that the opaque blob (the xattr) is the interface presented to user
    > > space. It isn't really used internally except to turn it into a data
    > > structure or to write it to disk for persistence.
    > That is the way that selinux does it, do the other lsms also handle it
    > this way?

    Casey handles this a different way in Smack but it has more to do with
    his model than his design. Since a Smack label is just a simple 23 byte
    string he doesn't do any conversion to store it in Smack. SELinux
    differs in that the label contains 4 components so these get broken out
    into the security structure so they can be handled separately by the
    security structure. I can't say for certain but I would probably say
    that a label based LSM which attempts to implement several models will
    probably have to do what SELinux does. The only thing I'm concerned with
    is that Casey did mention when I was creating hooks for the Labeled NFS
    work a situation where an LSM may implement multiple security.* xattrs.
    We don't currently have any LSMs that work that way so I'm not sure if I
    need to handle that now.

    > > The situation we have with sysfs is that there is no persistence for
    > > labels and the in-core inode maybe evicted so we need a way of
    > > persisting changes from the default label.
    > So you put it in the structure you did, which is correct. You should
    > also listen to all sysfs netlink messages to be sure to lable things
    > when they are created, to handle the lack of persistence.

    Thanks for the heads up. I'll make sure I look into this.

    > thanks,
    > greg k-h

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