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

[Steffen Klassert]

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.

I plan to apply the patch from Xin Long, this seems to be the right way
to address this problem.