lkml.org 
[lkml]   [2010]   [Apr]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 3/3] p9auth: add p9auth driver
    Quoting Eric W. Biederman (ebiederm@xmission.com):
    > "Serge E. Hallyn" <serue@us.ibm.com> writes:
    >
    > > Quoting Greg KH (greg@kroah.com):
    > >> On Tue, Apr 20, 2010 at 08:29:08PM -0500, Serge E. Hallyn wrote:
    > >> > This is a driver that adds Plan 9 style capability device
    > >> > implementation. See Documentation/p9auth.txt for a description
    > >> > of how to use this.
    > >>
    > >> Hm, you didn't originally write this driver, so it would be good to get
    > >> some original authorship information in here to keep everything correct,
    > >> right?
    > >
    > > That's why I left the MODULE_AUTHOR line in there - not sure what
    > > else to do for that. I'll add a comment in p9auth.txt, especially
    > > pointing back to Ashwin's original paper.
    > >
    > >> > Documentation/p9auth.txt | 47 ++++
    > >> > drivers/char/Kconfig | 2 +
    > >> > drivers/char/Makefile | 2 +
    > >> > drivers/char/p9auth/Kconfig | 9 +
    > >> > drivers/char/p9auth/Makefile | 1 +
    > >> > drivers/char/p9auth/p9auth.c | 517 ++++++++++++++++++++++++++++++++++++++++++
    > >>
    > >> Is this code really ready for drivers/char/? What has changed in it
    > >> that makes it ok to move out of the staging tree?
    > >
    > > It was dropped from staging :) I don't particularly care to see it
    > > go back into staging, as opposed to working out issues out of tree
    > > (assuming they are solvable). For one thing, as you note below,
    > > there is the question of whether it should be a device driver at
    > > all.
    > >
    > >> And who is going to maintain it? You? Or someone else?
    > >
    > > If Ashwin doesn't want to maintain it, I'll do it. Either way.
    > >
    > >> > 6 files changed, 578 insertions(+), 0 deletions(-)
    > >> > create mode 100644 Documentation/p9auth.txt
    > >> > create mode 100644 drivers/char/p9auth/Kconfig
    > >> > create mode 100644 drivers/char/p9auth/Makefile
    > >> > create mode 100644 drivers/char/p9auth/p9auth.c
    > >> >
    > >> > diff --git a/Documentation/p9auth.txt b/Documentation/p9auth.txt
    > >> > new file mode 100644
    > >> > index 0000000..14a69d8
    > >> > --- /dev/null
    > >> > +++ b/Documentation/p9auth.txt
    > >> > @@ -0,0 +1,47 @@
    > >> > +The p9auth device driver implements a plan-9 factotum-like
    > >> > +capability API. Tasks which are privileged (authorized by
    > >> > +possession of the CAP_GRANT_ID privilege (POSIX capability))
    > >> > +can write new capabilities to /dev/caphash. The kernel then
    > >> > +stores these until a task uses them by writing to the
    > >> > +/dev/capuse device. Each capability represents the ability
    > >> > +for a task running as userid X to switch to userid Y and
    > >> > +some set of groups. Each capability may be used only once,
    > >> > +and unused capabilities are cleared after two minutes.
    > >> > +
    > >> > +The following examples shows how to use the API. Shell 1
    > >> > +contains a privileged root shell. Shell 2 contains an
    > >> > +unprivileged shell as user 501 in the same user namespace. If
    > >> > +not already done, the privileged shell should create the p9auth
    > >> > +devices:
    > >> > +
    > >> > + majfile=/sys/module/p9auth/parameters/cap_major
    > >> > + minfile=/sys/module/p9auth/parameters/cap_minor
    > >> > + maj=`cat $majfile`
    > >> > + mknod /dev/caphash c $maj 0
    > >> > + min=`cat $minfile`
    > >> > + mknod /dev/capuse c $maj 1
    > >> > + chmod ugo+w /dev/capuse
    > >>
    > >> That is incorrect, you don't need the cap_major/minor files at all, the
    > >> device node should be automatically created for you, right?
    > >
    > > Hmm, where? Not in /dev on my SLES11 partition...
    > >
    > >> And do you really want to do all of this control through a device node?
    > >> Why?
    > >
    > > Well...
    > >
    > > At first I was thinking same as you were. So I was going to switch
    > > to a pure syscall-based approach. But it just turned out more
    > > complicated. The factotum server would call sys_grantid(), and
    > > the target task would end up doing some huge sys_setresugid() or
    > > else multiple syscalls using the granted id. It just was uglier.
    > > I think there's an experimental patchset sitting somewhere I could
    > > point to (if I weren't embarassed :).
    > >
    > > Another possibility would be to use netlink, but that doesn't
    > > appear as amenable to segragation by user namespaces. The pid
    > > (presumably/hopefully global pid, as __u32) is available, so it
    > > shouldn't be impossible, but a simple device with simple synchronous
    > > read/write certainly has its appeal. Firing off a message hoping
    > > that at some point our credentials will be changes, less so.
    >
    > pid in the netlink context is the netlink port-id. It is a very
    > different concept from struct pid. These days netlink calls to
    > the kernel are synchronous, not that I would encourage netlink
    > for anything except networking code.
    >
    > Can we make this a trivial filesystem? I expect that would match
    > up better with whatever plan9 userspace apps already exist,
    > remove the inode double translation, and would make it much more
    > reasonable to do a user namespace aware version if and when

    BTW, this current version is user namespace aware.

    > that becomes necessary.

    An fs actually seems overkill for two write-only files for
    process-related information. Would these actually be candidates
    for new /proc files?

    /proc/grantcred - replaces /dev/caphash, for privileged
    tasks to tell the kernel about new setuid
    capabilities
    /proc/self/usecred - replaces /dev/capuse for unprivileged
    tasks to make use of a setuid capability

    -serge


    \
     
     \ /
      Last update: 2010-04-24 05:39    [W:0.031 / U:0.524 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site