linux-kernel - Re: [PATCH v2] xfrm: policy: Fix xfrm policy match

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Date:   Sat, 23 May 2020 17:02:38 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Yuehaibing <yuehaibing@...wei.com>
Cc:     Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        davem <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
        network dev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] xfrm: policy: Fix xfrm policy match

On Fri, May 22, 2020 at 8:39 PM Yuehaibing <yuehaibing@...wei.com> wrote:
>
> On 2020/5/22 13:49, Xin Long wrote:
> > On Fri, May 22, 2020 at 9:45 AM Yuehaibing <yuehaibing@...wei.com> wrote:
> >>
> >> On 2020/5/21 14:49, Xin Long wrote:
> >>> On Tue, May 19, 2020 at 4:53 PM Steffen Klassert
> >>> <steffen.klassert@...unet.com> wrote:
> >>>>
> >>>> On Fri, May 15, 2020 at 04:39:57PM +0800, Yuehaibing wrote:
> >>>>>
> >>>>> Friendly ping...
> >>>>>
> >>>>> Any plan for this issue?
> >>>>
> >>>> There was still no consensus between you and Xin on how
> >>>> to fix this issue. Once this happens, I consider applying
> >>>> a fix.
> >>>>
> >>> Sorry, Yuehaibing, I can't really accept to do: (A->mark.m & A->mark.v)
> >>> I'm thinking to change to:
> >>>
> >>>  static bool xfrm_policy_mark_match(struct xfrm_policy *policy,
> >>>                                    struct xfrm_policy *pol)
> >>>  {
> >>> -       u32 mark = policy->mark.v & policy->mark.m;
> >>> -
> >>> -       if (policy->mark.v == pol->mark.v && policy->mark.m == pol->mark.m)
> >>> -               return true;
> >>> -
> >>> -       if ((mark & pol->mark.m) == pol->mark.v &&
> >>> -           policy->priority == pol->priority)
> >>> +       if (policy->mark.v == pol->mark.v &&
> >>> +           (policy->mark.m == pol->mark.m ||
> >>> +            policy->priority == pol->priority))
> >>>                 return true;
> >>>
> >>>         return false;
> >>>
> >>> which means we consider (the same value and mask) or
> >>> (the same value and priority) as the same one. This will
> >>> cover both problems.
> >>
> >>   policy A (mark.v = 0x1011, mark.m = 0x1011, priority = 1)
> >>   policy B (mark.v = 0x1001, mark.m = 0x1001, priority = 1)
> > I'd think these are 2 different policies.
> >
> >>
> >>   when fl->flowi_mark == 0x12341011, in xfrm_policy_match() do check like this:
> >>
> >>         (fl->flowi_mark & pol->mark.m) != pol->mark.v
> >>
> >>         0x12341011 & 0x1011 == 0x00001011
> >>         0x12341011 & 0x1001 == 0x00001001
> >>
> >>  This also match different policy depends on the order of policy inserting.
> > Yes, this may happen when a user adds 2  policies like that.
> > But I think this's a problem that the user doesn't configure it well,
> > 'priority' should be set.
> > and this can not be avoided, also such as:
> >
> >    policy A (mark.v = 0xff00, mark.m = 0x1000, priority = 1)
> >    policy B (mark.v = 0x00ff, mark.m = 0x0011, priority = 1)
> >
> >    try with 0x12341011
> >
> > So just be it, let users decide.
>
> Ok, this make sense.
Thanks Yuehaibing, it's good we're on the same page now.

Just realized the patch I created above won't work for the case:

  policy A (mark.v = 0x10, mark.m = 0, priority = 1)
  policy B (mark.v = 0x1,  mark.m = 0, priority = 2)
  policy C (mark.v = 0x10, mark.m = 0, priority = 2)

when policy C is being added, the warning still occurs.

So I will just check value and priority:
-       u32 mark = policy->mark.v & policy->mark.m;
-
-       if (policy->mark.v == pol->mark.v && policy->mark.m == pol->mark.m)
-               return true;
-
-       if ((mark & pol->mark.m) == pol->mark.v &&
+       if (policy->mark.v == pol->mark.v &&
            policy->priority == pol->priority)
                return true;

This allows two policies like this exist:

  policy A (mark.v = 0x10, mark.m = 0, priority = 1)
  policy C (mark.v = 0x10, mark.m = 0, priority = 2)

But I don't think it's a problem.