linux-kernel - Re: [PATCH] device_cgroup: Roll back to original exceptions after copy failure

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Date:   Tue, 15 Nov 2022 15:55:58 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     wangweiyang <wangweiyang2@...wei.com>
Cc:     jmorris@...ei.org, serge@...lyn.com, serge.hallyn@...onical.com,
        akpm@...ux-foundation.org, aris@...hat.com,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] device_cgroup: Roll back to original exceptions after
 copy failure

On Mon, Nov 14, 2022 at 10:54 PM wangweiyang <wangweiyang2@...wei.com> wrote:
>
> Hi, Paul
> Can this patch be applied or something to improve?

Possibly.  I need to find the time to properly review the patch; it's
in my queue, I just haven't gotten to it yet.  I'll reply to the patch
posting with either a note that the patch has been merged, or a set of
questions/feedback that needs to be resolved.  If you haven't heard
from me on the patch, the best thing you can do is exercise patience.

> on 2022/10/28 19:19, Paul Moore wrote:
> > On Tue, Oct 25, 2022 at 7:02 AM Wang Weiyang <wangweiyang2@...wei.com> wrote:
> >>
> >> When add the 'a *:* rwm' entry to devcgroup A's whitelist, at first A's
> >> exceptions will be cleaned and A's behavior is changed to
> >> DEVCG_DEFAULT_ALLOW. Then parent's exceptions will be copyed to A's
> >> whitelist. If copy failure occurs, just return leaving A to grant
> >> permissions to all devices. And A may grant more permissions than
> >> parent.
> >>
> >> Backup A's whitelist and recover original exceptions after copy
> >> failure.
> >>
> >> Fixes: 4cef7299b478 ("device_cgroup: add proper checking when changing default behavior")
> >> Signed-off-by: Wang Weiyang <wangweiyang2@...wei.com>
> >> ---
> >>  security/device_cgroup.c | 33 +++++++++++++++++++++++++++++----
> >>  1 file changed, 29 insertions(+), 4 deletions(-)
> >
> > On quick glance this looks reasonable to me, but I'm working with
> > limited time connected to a network so I can't say I've given this a
> > full and proper review; if a third party could spend some time to give
> > this an additional review before I merge it I would greatly appreciate
> > it.
> >
> >> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> >> index a9f8c63a96d1..bef2b9285fb3 100644
> >> --- a/security/device_cgroup.c
> >> +++ b/security/device_cgroup.c
> >> @@ -82,6 +82,17 @@ static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
> >>         return -ENOMEM;
> >>  }
> >>
> >> +static void dev_exceptions_move(struct list_head *dest, struct list_head *orig)
> >> +{
> >> +       struct dev_exception_item *ex, *tmp;
> >> +
> >> +       lockdep_assert_held(&devcgroup_mutex);
> >> +
> >> +       list_for_each_entry_safe(ex, tmp, orig, list) {
> >> +               list_move_tail(&ex->list, dest);
> >> +       }
> >> +}
> >> +
> >>  /*
> >>   * called under devcgroup_mutex
> >>   */
> >> @@ -604,11 +615,13 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
> >>         int count, rc = 0;
> >>         struct dev_exception_item ex;
> >>         struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
> >> +       struct dev_cgroup tmp_devcgrp;
> >>
> >>         if (!capable(CAP_SYS_ADMIN))
> >>                 return -EPERM;
> >>
> >>         memset(&ex, 0, sizeof(ex));
> >> +       memset(&tmp_devcgrp, 0, sizeof(tmp_devcgrp));
> >>         b = buffer;
> >>
> >>         switch (*b) {
> >> @@ -620,15 +633,27 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
> >>
> >>                         if (!may_allow_all(parent))
> >>                                 return -EPERM;
> >> -                       dev_exception_clean(devcgroup);
> >> -                       devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
> >> -                       if (!parent)
> >> +                       if (!parent) {
> >> +                               devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
> >> +                               dev_exception_clean(devcgroup);
> >>                                 break;
> >> +                       }
> >>
> >> +                       INIT_LIST_HEAD(&tmp_devcgrp.exceptions);
> >> +                       rc = dev_exceptions_copy(&tmp_devcgrp.exceptions,
> >> +                                                &devcgroup->exceptions);
> >> +                       if (rc)
> >> +                               return rc;
> >> +                       dev_exception_clean(devcgroup);
> >>                         rc = dev_exceptions_copy(&devcgroup->exceptions,
> >>                                                  &parent->exceptions);
> >> -                       if (rc)
> >> +                       if (rc) {
> >> +                               dev_exceptions_move(&devcgroup->exceptions,
> >> +                                                   &tmp_devcgrp.exceptions);
> >>                                 return rc;
> >> +                       }
> >> +                       devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
> >> +                       dev_exception_clean(&tmp_devcgrp);
> >>                         break;
> >>                 case DEVCG_DENY:
> >>                         if (css_has_online_children(&devcgroup->css))
> >> --
> >> 2.17.1
> >>
> >
> >



-- 
paul-moore.com