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    SubjectRe: [PATCH 2/2] debugfs: only allow root access to debugging interfaces
    On Tue, Feb 22, 2011 at 12:28:56PM -0800, Kees Cook wrote:
    > On Tue, Feb 22, 2011 at 12:16:10PM -0800, Greg KH wrote:
    > > On Tue, Feb 22, 2011 at 11:50:18AM -0800, Kees Cook wrote:
    > > > On Tue, Feb 22, 2011 at 07:34:18PM +0000, Alan Cox wrote:
    > > > > > What system do you proposed to keep these "stupid mistakes" from
    > > > > > continuing to happen? If debugfs had already been mode 0700, we could have
    > > > > > avoided all of these CVEs, including the full-blown local root escalation.
    > > > >
    > > > > And all sorts of features would have put themselves in sysfs instead and
    > > > > broken no doubt.
    > > > >
    > > > > > The "no rules" approach to debugfs is not a good idea, IMO.
    > > > >
    > > > > It's a debugging fs, it needs to be "no rules" other than the obvious
    > > > > "don't mount it on production systems"
    > > >
    > > > Okay, so the debugfs is not supposed to be mounted on a production system.
    > >
    > > No, not true at all, the "enterprise" distros all mount debugfs for good
    > > reason on their systems.
    >
    > What reasons are those? Or better yet, why do you and Alan Cox disagree on
    > this point?

    These distros have made the decision to support the perf interface,
    which lives in debugfs, for their customers. I'm not saying that I
    disagree with Alan about this, just pointing out the reality of the
    situation here.

    > > > This seems to be news to a lot of developers trying to use the interfaces
    > > > exposed there. It would be nice to say this more loudly. Basically,
    > > > a normal system should not depend on anything in the debugfs. I can get
    > > > behind that.
    > >
    > > Again, not true. Mostly all due to the perf interface, fix that to move
    > > out of debugfs (patches have been proposed) and this problem will go
    > > away.
    >
    > You can't have "no rules" and "all distros mount debugfs for good reason".
    > This is asking for (even more) trouble. If there is something universally
    > useful in debugfs (I do not count perf as universally useful -- my parents
    > do not use perf), then why is it living in a filesystem with no rules
    > (where "no rules" seems to also include "don't break interfaces").

    Again, "don't break interfaces" is just me saying "don't break the
    interfaces I have created in debugfs as they are to be used by all
    users." Don't take that as a set-in-stone rule of debugfs at all, it
    isn't.

    Again, you are trying to exclude a whole range of useful and valid files
    from being used, when there was only a very very very small percentage
    created incorrectly. They have now been fixed, and we have the
    infrastructure to prevent future ones from being created as well, so I
    don't see the issue here anymore.

    thanks,

    greg k-h


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