[RFC] xfrm: fix handling of XFRM policies mark and mask.

On Wed, Feb 06, 2013 at 02:53:48PM +0100, Emmanuel Thierry wrote:
> 
> Hello,
> 
> Le 6 févr. 2013 à 14:14, jamal a écrit :
> 
> > 
> > On 13-02-05 03:12 AM, Steffen Klassert wrote:
> >>> For example, executing the below commands in that order succeed:
> >>>  ip -6 xfrm policy flush
> >>>  ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 1 mask 0xffffffff
> >>>  ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out
> >> The policy with mark 1 is the first we find. The policy passes the
> >> mark check and if the flow matches the selectors, we use this policy.
> >> 
> >>> But it fails in the reverse order:
> >>>  ip -6 xfrm policy flush
> >>>  ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out
> >>>  ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 1 mask 0xffffffff
> >>>  RTNETLINK answers: File exists
> >> With this scenario, we would find the policy with mark and mask 0 first.
> >> This policy passes the mark check too. So we would use this policy if the
> >> flow matches the selectors, but the flow asked for a policy with mark 1.
> > 
> > I think the intent Romain is expressing is reasonable and should resolved at
> > insertion time(xfrm_policy_insert()).
> > i.e even though the policy (such as mark=1) is inserted afterwards, at
> > insertion time if it proves it is more specific and not duplicate, it should be
> > inserted ahead of the mark=0.
> > The runtime check will work then.
> 
> Actually, we didn't think about this problem since we work with priorities, putting the default policy (without a mark) at a minor priority than the marked one.
> Your remark makes clearer the ideas behind the design of XFRM, but this leads to an interesting concern. If on policy insertion, the policy were inserted depending on the accuracy of the mark (the more the mask is specific, the more the mark must be put at the beginning of the list), how would we decide which is the more specific between these ones ?
> 
> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 0x00000001 mask 0x00000005
> 
> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 0x00000001 mask 0x00000003
> 

We can't decide on the order of these two policies, so we should not
allow to insert both. At least not if the have the same priority,
but we could insert both if they have different priorities.

Would the patch below meet your requirements?

---
 net/xfrm/xfrm_policy.c |   18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)

Hello,

Le 7 févr. 2013 à 11:49, Steffen Klassert <steffen.klassert@secunet.com> a écrit :

> On Wed, Feb 06, 2013 at 02:53:48PM +0100, Emmanuel Thierry wrote:
>> 
>> Le 6 févr. 2013 à 14:14, jamal a écrit :
>> 
>>> 
>>> On 13-02-05 03:12 AM, Steffen Klassert wrote:
>>>>> For example, executing the below commands in that order succeed:
>>>>> ip -6 xfrm policy flush
>>>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 1 mask 0xffffffff
>>>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out
>>>> The policy with mark 1 is the first we find. The policy passes the
>>>> mark check and if the flow matches the selectors, we use this policy.
>>>> 
>>>>> But it fails in the reverse order:
>>>>> ip -6 xfrm policy flush
>>>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out
>>>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 1 mask 0xffffffff
>>>>> RTNETLINK answers: File exists
>>>> With this scenario, we would find the policy with mark and mask 0 first.
>>>> This policy passes the mark check too. So we would use this policy if the
>>>> flow matches the selectors, but the flow asked for a policy with mark 1.
>>> 
>>> I think the intent Romain is expressing is reasonable and should resolved at
>>> insertion time(xfrm_policy_insert()).
>>> i.e even though the policy (such as mark=1) is inserted afterwards, at
>>> insertion time if it proves it is more specific and not duplicate, it should be
>>> inserted ahead of the mark=0.
>>> The runtime check will work then.
>> 
>> Actually, we didn't think about this problem since we work with priorities, putting the default policy (without a mark) at a minor priority than the marked one.
>> Your remark makes clearer the ideas behind the design of XFRM, but this leads to an interesting concern. If on policy insertion, the policy were inserted depending on the accuracy of the mark (the more the mask is specific, the more the mark must be put at the beginning of the list), how would we decide which is the more specific between these ones ?
>> 
>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 0x00000001 mask 0x00000005
>> 
>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 0x00000001 mask 0x00000003
>> 
> 
> We can't decide on the order of these two policies, so we should not
> allow to insert both. At least not if the have the same priority,
> but we could insert both if they have different priorities.
> 
> Would the patch below meet your requirements?
> 
> ---
> net/xfrm/xfrm_policy.c |   18 ++++++++++++++++--
> 1 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index 6c9aa64..b169a69 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -562,6 +562,21 @@ static inline int selector_cmp(struct xfrm_selector *s1, struct xfrm_selector *s
> 	return 0;
> }
> 
> +static bool xfrm_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)
> +		return true;
> +
> +	return false;
> +}
> +
> int xfrm_policy_insert(int dir, struct xfrm_policy *policy, int excl)
> {
> 	struct net *net = xp_net(policy);
> @@ -569,7 +584,6 @@ int xfrm_policy_insert(int dir, struct xfrm_policy *policy, int excl)
> 	struct xfrm_policy *delpol;
> 	struct hlist_head *chain;
> 	struct hlist_node *entry, *newpos;
> -	u32 mark = policy->mark.v & policy->mark.m;
> 
> 	write_lock_bh(&xfrm_policy_lock);
> 	chain = policy_hash_bysel(net, &policy->selector, policy->family, dir);
> @@ -578,7 +592,7 @@ int xfrm_policy_insert(int dir, struct xfrm_policy *policy, int excl)
> 	hlist_for_each_entry(pol, entry, chain, bydst) {
> 		if (pol->type == policy->type &&
> 		    !selector_cmp(&pol->selector, &policy->selector) &&
> -		    (mark & pol->mark.m) == pol->mark.v &&
> +		    xfrm_mark_match(policy, pol) &&
> 		    xfrm_sec_ctx_match(pol->security, policy->security) &&
> 		    !WARN_ON(delpol)) {
> 			if (excl) {
> -- 
> 1.7.2.5
> 

This is a nice idea, however you keep the insertion asymmetric. The usage of xfrm marks in non-conflicting cases will be made possible, but it stays disturbing for a user as the initial example will still have the same behavior:
* Inserting the marked one then the unmarked will succeed
* Inserting the unmarked then the marked one will fail
This gives to the user the feeling of an indeterministic behavior of the xfrm module.

On the base of your patch, i'd propose to make it symmetric (handmade patch below).

Best regards
Emmanuel Thierry

--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c

 static bool xfrm_mark_match(struct xfrm_policy *policy,
 			    struct xfrm_policy *pol)
 {
 	u32 mark = policy->mark.v & policy->mark.m;
+	u32 mark2 = pol->mark.v & pol->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 &&
+	    (mark2 & policy->mark.m) == policy->mark.v &&
 	    policy->priority == pol->priority)
 		return true;
 
 	return false;
 }


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Le 7 févr. 2013 à 12:08, Emmanuel Thierry <emmanuel.thierry@telecom-bretagne.eu> a écrit :

> Hello,
> 
> Le 7 févr. 2013 à 11:49, Steffen Klassert <steffen.klassert@secunet.com> a écrit :
> 
>> On Wed, Feb 06, 2013 at 02:53:48PM +0100, Emmanuel Thierry wrote:
>>> 
>>> Le 6 févr. 2013 à 14:14, jamal a écrit :
>>> 
>>>> 
>>>> On 13-02-05 03:12 AM, Steffen Klassert wrote:
>>>>>> For example, executing the below commands in that order succeed:
>>>>>> ip -6 xfrm policy flush
>>>>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 1 mask 0xffffffff
>>>>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out
>>>>> The policy with mark 1 is the first we find. The policy passes the
>>>>> mark check and if the flow matches the selectors, we use this policy.
>>>>> 
>>>>>> But it fails in the reverse order:
>>>>>> ip -6 xfrm policy flush
>>>>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out
>>>>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 1 mask 0xffffffff
>>>>>> RTNETLINK answers: File exists
>>>>> With this scenario, we would find the policy with mark and mask 0 first.
>>>>> This policy passes the mark check too. So we would use this policy if the
>>>>> flow matches the selectors, but the flow asked for a policy with mark 1.
>>>> 
>>>> I think the intent Romain is expressing is reasonable and should resolved at
>>>> insertion time(xfrm_policy_insert()).
>>>> i.e even though the policy (such as mark=1) is inserted afterwards, at
>>>> insertion time if it proves it is more specific and not duplicate, it should be
>>>> inserted ahead of the mark=0.
>>>> The runtime check will work then.
>>> 
>>> Actually, we didn't think about this problem since we work with priorities, putting the default policy (without a mark) at a minor priority than the marked one.
>>> Your remark makes clearer the ideas behind the design of XFRM, but this leads to an interesting concern. If on policy insertion, the policy were inserted depending on the accuracy of the mark (the more the mask is specific, the more the mark must be put at the beginning of the list), how would we decide which is the more specific between these ones ?
>>> 
>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 0x00000001 mask 0x00000005
>>> 
>>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 0x00000001 mask 0x00000003
>>> 
>> 
>> We can't decide on the order of these two policies, so we should not
>> allow to insert both. At least not if the have the same priority,
>> but we could insert both if they have different priorities.
>> 
>> Would the patch below meet your requirements?
>> 
>> ---
>> net/xfrm/xfrm_policy.c |   18 ++++++++++++++++--
>> 1 files changed, 16 insertions(+), 2 deletions(-)
>> 
>> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
>> index 6c9aa64..b169a69 100644
>> --- a/net/xfrm/xfrm_policy.c
>> +++ b/net/xfrm/xfrm_policy.c
>> @@ -562,6 +562,21 @@ static inline int selector_cmp(struct xfrm_selector *s1, struct xfrm_selector *s
>> 	return 0;
>> }
>> 
>> +static bool xfrm_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)
>> +		return true;
>> +
>> +	return false;
>> +}
>> +
>> int xfrm_policy_insert(int dir, struct xfrm_policy *policy, int excl)
>> {
>> 	struct net *net = xp_net(policy);
>> @@ -569,7 +584,6 @@ int xfrm_policy_insert(int dir, struct xfrm_policy *policy, int excl)
>> 	struct xfrm_policy *delpol;
>> 	struct hlist_head *chain;
>> 	struct hlist_node *entry, *newpos;
>> -	u32 mark = policy->mark.v & policy->mark.m;
>> 
>> 	write_lock_bh(&xfrm_policy_lock);
>> 	chain = policy_hash_bysel(net, &policy->selector, policy->family, dir);
>> @@ -578,7 +592,7 @@ int xfrm_policy_insert(int dir, struct xfrm_policy *policy, int excl)
>> 	hlist_for_each_entry(pol, entry, chain, bydst) {
>> 		if (pol->type == policy->type &&
>> 		    !selector_cmp(&pol->selector, &policy->selector) &&
>> -		    (mark & pol->mark.m) == pol->mark.v &&
>> +		    xfrm_mark_match(policy, pol) &&
>> 		    xfrm_sec_ctx_match(pol->security, policy->security) &&
>> 		    !WARN_ON(delpol)) {
>> 			if (excl) {
>> -- 
>> 1.7.2.5
>> 
> 
> This is a nice idea, however you keep the insertion asymmetric. The usage of xfrm marks in non-conflicting cases will be made possible, but it stays disturbing for a user as the initial example will still have the same behavior:
> * Inserting the marked one then the unmarked will succeed
> * Inserting the unmarked then the marked one will fail
> This gives to the user the feeling of an indeterministic behavior of the xfrm module.
> 
> On the base of your patch, i'd propose to make it symmetric (handmade patch below).
> 
> Best regards
> Emmanuel Thierry


Excuse the problem of logic, i sent it too quickly, here is the correct proposal:


--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c

 static bool xfrm_mark_match(struct xfrm_policy *policy,
 			    struct xfrm_policy *pol)
 {
 	u32 mark = policy->mark.v & policy->mark.m;
+	u32 mark2 = pol->mark.v & pol->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 (((mark & pol->mark.m) == pol->mark.v ||
+	    (mark2 & policy->mark.m) == policy->mark.v) &&
 	    policy->priority == pol->priority)
 		return true;
 
 	return false;
 }





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On Thu, Feb 07, 2013 at 12:08:22PM +0100, Emmanuel Thierry wrote:
> 
> This is a nice idea, however you keep the insertion asymmetric. The usage of xfrm marks in non-conflicting cases will be made possible, but it stays disturbing for a user as the initial example will still have the same behavior:
> * Inserting the marked one then the unmarked will succeed
> * Inserting the unmarked then the marked one will fail
> This gives to the user the feeling of an indeterministic behavior of the xfrm module.

This was intended. Inserting the marked one then the unmarked
is a working scenario. Some users might rely on it, so we can't
change this as you proposed.

On the other hand, inserting the unmarked one then the marked
might result in a wrong policy lookup, so we can't allow this.
The only possibility we have, is inserting with different
priorites and that's what I'm proposing.

I fear we have to live with that asymmetric behaviour if
both policies have the same priority.

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Hello,

Le 7 févr. 2013 à 13:54, Steffen Klassert <steffen.klassert@secunet.com> a écrit :

> On Thu, Feb 07, 2013 at 12:08:22PM +0100, Emmanuel Thierry wrote:
>> 
>> This is a nice idea, however you keep the insertion asymmetric. The usage of xfrm marks in non-conflicting cases will be made possible, but it stays disturbing for a user as the initial example will still have the same behavior:
>> * Inserting the marked one then the unmarked will succeed
>> * Inserting the unmarked then the marked one will fail
>> This gives to the user the feeling of an indeterministic behavior of the xfrm module.
> 
> This was intended. Inserting the marked one then the unmarked
> is a working scenario. Some users might rely on it, so we can't
> change this as you proposed.
> 
> On the other hand, inserting the unmarked one then the marked
> might result in a wrong policy lookup, so we can't allow this.
> The only possibility we have, is inserting with different
> priorites and that's what I'm proposing.
> 
> I fear we have to live with that asymmetric behaviour if
> both policies have the same priority.
> 

Ok, actually i understand the concern of backward compatibility you expose. It is true that users might be disturbed if we change such a behavior they would rely on.
Anyway, i'm ok with your patch.

Best regards
Emmanuel Thierry--
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Hi Steffen,

Do you plan to resubmit a patch to the mailing list or shall we take care of that?

Thank you,
Romain

On Feb 8, 2013, at 15:16 , Emmanuel Thierry <emmanuel.thierry@telecom-bretagne.eu> wrote:

> Hello,
> 
> Le 7 févr. 2013 à 13:54, Steffen Klassert <steffen.klassert@secunet.com> a écrit :
> 
>> On Thu, Feb 07, 2013 at 12:08:22PM +0100, Emmanuel Thierry wrote:
>>> 
>>> This is a nice idea, however you keep the insertion asymmetric. The usage of xfrm marks in non-conflicting cases will be made possible, but it stays disturbing for a user as the initial example will still have the same behavior:
>>> * Inserting the marked one then the unmarked will succeed
>>> * Inserting the unmarked then the marked one will fail
>>> This gives to the user the feeling of an indeterministic behavior of the xfrm module.
>> 
>> This was intended. Inserting the marked one then the unmarked
>> is a working scenario. Some users might rely on it, so we can't
>> change this as you proposed.
>> 
>> On the other hand, inserting the unmarked one then the marked
>> might result in a wrong policy lookup, so we can't allow this.
>> The only possibility we have, is inserting with different
>> priorites and that's what I'm proposing.
>> 
>> I fear we have to live with that asymmetric behaviour if
>> both policies have the same priority.
>> 
> 
> Ok, actually i understand the concern of backward compatibility you expose. It is true that users might be disturbed if we change such a behavior they would rely on.
> Anyway, i'm ok with your patch.
> 
> Best regards
> Emmanuel Thierry