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

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Date:   Wed, 22 Apr 2020 23:41:37 +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>, kuba@...nel.org,
        network dev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfrm: policy: Only use mark as policy lookup key

On Wed, Apr 22, 2020 at 8:18 PM Yuehaibing <yuehaibing@...wei.com> 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@...wei.com>
> >> ---
> >>  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)

>
>
>
> >
> > .
> >
>