Re: [PATCH] xfrm: policy: Only use mark as policy lookup key

From: Xin Long
Date: Thu Apr 23 2020 - 05:38:19 EST

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On Thu, Apr 23, 2020 at 4:41 PM Yuehaibing <yuehaibing@xxxxxxxxxx> wrote:
>
> On 2020/4/23 14:37, Xin Long wrote:
> > On Thu, Apr 23, 2020 at 10:26 AM Yuehaibing <yuehaibing@xxxxxxxxxx> wrote:
> >>
> >> On 2020/4/22 23:41, Xin Long wrote:
> >>> On Wed, Apr 22, 2020 at 8:18 PM Yuehaibing <yuehaibing@xxxxxxxxxx> wrote:
> >>>>
> >>>> On 2020/4/22 17:33, Steffen Klassert wrote:
> >>>>> On Tue, Apr 21, 2020 at 10:31:49PM +0800, YueHaibing wrote:
> >>>>>> While update xfrm policy as follow:
> >>>>>>
> >>>>>> ip -6 xfrm policy update src fd00::1/128 dst fd00::2/128 dir in \
> >>>>>> priority 1 mark 0 mask 0x10
> >>>>>> ip -6 xfrm policy update src fd00::1/128 dst fd00::2/128 dir in \
> >>>>>> priority 2 mark 0 mask 0x00
> >>>>>> ip -6 xfrm policy update src fd00::1/128 dst fd00::2/128 dir in \
> >>>>>> priority 2 mark 0 mask 0x10
> >>>>>>
> >>>>>> We get this warning:
> >>>>>>
> >>>>>> WARNING: CPU: 0 PID: 4808 at net/xfrm/xfrm_policy.c:1548
> >>>>>> Kernel panic - not syncing: panic_on_warn set ...
> >>>>>> CPU: 0 PID: 4808 Comm: ip Not tainted 5.7.0-rc1+ #151
> >>>>>> Call Trace:
> >>>>>> RIP: 0010:xfrm_policy_insert_list+0x153/0x1e0
> >>>>>> xfrm_policy_inexact_insert+0x70/0x330
> >>>>>> xfrm_policy_insert+0x1df/0x250
> >>>>>> xfrm_add_policy+0xcc/0x190 [xfrm_user]
> >>>>>> xfrm_user_rcv_msg+0x1d1/0x1f0 [xfrm_user]
> >>>>>> netlink_rcv_skb+0x4c/0x120
> >>>>>> xfrm_netlink_rcv+0x32/0x40 [xfrm_user]
> >>>>>> netlink_unicast+0x1b3/0x270
> >>>>>> netlink_sendmsg+0x350/0x470
> >>>>>> sock_sendmsg+0x4f/0x60
> >>>>>>
> >>>>>> Policy C and policy A has the same mark.v and mark.m, so policy A is
> >>>>>> matched in first round lookup while updating C. However policy C and
> >>>>>> policy B has same mark and priority, which also leads to matched. So
> >>>>>> the WARN_ON is triggered.
> >>>>>>
> >>>>>> xfrm policy lookup should only be matched when the found policy has the
> >>>>>> same lookup keys (mark.v & mark.m) no matter priority.
> >>>>>>
> >>>>>> Fixes: 7cb8a93968e3 ("xfrm: Allow inserting policies with matching mark and different priorities")
> >>>>>> Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
> >>>>>> ---
> >>>>>> net/xfrm/xfrm_policy.c | 16 +++++-----------
> >>>>>> 1 file changed, 5 insertions(+), 11 deletions(-)
> >>>>>>
> >>>>>> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> >>>>>> index 297b2fd..67d0469 100644
> >>>>>> --- a/net/xfrm/xfrm_policy.c
> >>>>>> +++ b/net/xfrm/xfrm_policy.c
> >>>>>> @@ -1436,13 +1436,7 @@ static void xfrm_policy_requeue(struct xfrm_policy *old,
> >>>>>> 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 you remove the priority check, you can't insert policies with matching
> >>>>> mark and different priorities anymore. This brings us back the old bug.
> >>>>
> >>>> Yes, this is true.
> >>>>
> >>>>>
> >>>>> I plan to apply the patch from Xin Long, this seems to be the right way
> >>>>> to address this problem.
> >>>>
> >>>> That still brings an issue, update like this:
> >>>>
> >>>> policy A (mark.v = 1, mark.m = 0, priority = 1)
> >>>> policy B (mark.v = 1, mark.m = 0, priority = 1)
> >>>>
> >>>> A and B will all in the list.
> >>> I think this is another issue even before:
> >>> 7cb8a93968e3 ("xfrm: Allow inserting policies with matching mark and
> >>> different priorities")
> >>>
> >>>>
> >>>> So should do this:
> >>>>
> >>>> 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 &&
> >>>> + if ((policy->mark.v & policy->mark.m) == (pol->mark.v & pol->mark.m) &&
> >>>> policy->priority == pol->priority)
> >>>> return true;
> >>> "mark.v & mark.m" looks weird to me, it should be:
> >>> ((something & mark.m) == mark.v)
> >>>
> >>> So why should we just do this here?:
> >>> (policy->mark.v == pol->mark.v && policy->mark.m == pol->mark.m &&
> >>> policy->priority == pol->priority)
> >>
> >>
> >> This leads to this issue:
> >>
> >> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir in mark 0x00000001 mask 0x00000005
> >> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir in mark 0x00000001 mask 0x00000003
> >>
> >> the two policies will be in list, which should not be allowed.
> > I think these are two different policies.
> > For instance:
> > mark = 0x1234567b will match the 1st one only.
> > mark = 0x1234567d will match the 2st one only
> >
> > So these should have been allowed, no?
>
> If mark = 0x12345671, it may match different policy depends on the order of inserting,
>
> ip xfrm policy update src 172.16.2.0/24 dst 172.16.1.0/24 dir in ptype main \
> tmpl src 192.168.2.10 dst 192.168.1.20 proto esp mode tunnel mark 0x00000001 mask 0x00000005
>
> ip xfrm policy update src 172.16.2.0/24 dst 172.16.1.0/24 dir in ptype main \
> tmpl src 192.168.2.100 dst 192.168.1.100 proto esp mode beet mark 0x00000001 mask 0x00000003
>
> In fact, your case should use different priority to match.
Sorry, but it does match your above policies now, like in xfrm_policy_match(),
when fl->flowi_mark == 0x1234567b:

(fl->flowi_mark & pol->mark.m) != pol->mark.v
0x1234567b & 0x00000005 == 0x00000001

and when fl->flowi_mark == 0x1234567d:
0x1234567d & 0x00000003 == 0x00000001

am I missing something?

>
> >
> > I'm actually confused now.
> > does the mask work against its own value, or the other value?
> > as 'A == (mark.v&mark.m)' and '(A & mark.m) == mark.v' are different things.
> >
> > This can date back to Jamal's xfrm by MARK:
> >
> > https://lwn.net/Articles/375829/
> >
> > where it does 'm->v & m->m' in xfrm_mark_get() and
> > 'policy->mark.v & policy->mark.m' in xfrm_policy_insert() while
> > it does '(A & pol->mark.m) == pol->mark.v' in other places.
> >
> > Now I'm thinking 'm->v & m->m' is meaningless, by which if we get
> > a value != m->v, it means this mark can never be matched by any.
> >
> > policy A (mark.v = 1, mark.m = 0, priority = 1)
> > policy B (mark.v = 1, mark.m = 0, priority = 1)
> >
> > So probably we should avoid this case by check m->v == (m->v & m->m)
> > when adding a new policy.
> >
> > wdyt?
> >
>

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