batctl: Validate translated mac addresses

Message ID 20180413181618.24144-1-sven@narfation.org
State Accepted, archived
Commit 9f22e3d0ed2a3d83479f3db3b570f49218024249
Delegated to: Simon Wunderlich
Headers show
Series
  • batctl: Validate translated mac addresses
Related show

Commit Message

Sven Eckelmann April 13, 2018, 6:16 p.m.
The IP translation layer is using the neighbor table of the kernel to get
the unicast link layer (mac) address for IP(v4|v6) addresses. The kernel
can not only return unicast mac addresses to such an RTM_GETNEIGH request
but also zero mac address. Such an address must be considered invalid
because the global translation table may not only contain a unique client
mac address entry for it. The translation from client mac to originator
will therefore most likely return an unexpected originator.

Dropping these kind of (bogus) results avoids confusions while using things
like batctl's ping or traceroute.

Reported-by: Andre Kasper <Andre.Kasper@gmx.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
Cc: Andre Kasper <Andre.Kasper@gmx.de>

See https://www.open-mesh.org/issues/353
---
 functions.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

Comments

Antonio Quartulli April 14, 2018, 2:34 a.m. | #1
On 14/04/18 02:16, Sven Eckelmann wrote:
> The IP translation layer is using the neighbor table of the kernel to get
> the unicast link layer (mac) address for IP(v4|v6) addresses. The kernel
> can not only return unicast mac addresses to such an RTM_GETNEIGH request
> but also zero mac address. Such an address must be considered invalid
> because the global translation table may not only contain a unique client
> mac address entry for it. The translation from client mac to originator
> will therefore most likely return an unexpected originator.
> 

We already handle the case of multiple originators handling the same MAC
address, no? In that case I think we pick the "best" originator.

This case sounds more like a validity check because "a zero MAC should
not be in the translation table", or am I wrong?


Cheers,
Sven Eckelmann April 14, 2018, 7:10 a.m. | #2
On Samstag, 14. April 2018 04:34:42 CEST Antonio Quartulli wrote:
> 
> On 14/04/18 02:16, Sven Eckelmann wrote:
[...]
> We already handle the case of multiple originators handling the same MAC
> address, no? In that case I think we pick the "best" originator.

Yes, but this doesn't make a lot of sense for multicast and zero mac 
addresses. The translate layer of batctl is usually used to ping/traceroute to 
some originator. But multicast and zero mac addresses don't represent a 
"client" which can be used to identify some originator. So it doesn't seem to 
make sense to allow them here.

Or even without the ping/traceroute stuff, the concept of calling `batctl 
translate` should give you an answer which you can understand. So it should 
tell you that batman-adv is very likely to transmit a unicast packet with this 
destination address to this originator. But this cannot work for multicast 
destination addresses because multiple answer should be given here - which is 
out of scope for this command. Which reminds me that I should propose a second 
patch which checks whether the input for translate_mac is "valid" before 
trying to translate it.

> This case sounds more like a validity check because "a zero MAC should
> not be in the translation table", or am I wrong?

Partially, yes. I personally don't care (at the moment) whether there is a 
zero mac address in the translation table. The current translation table code 
(batadv_tt_local_add) doesn't check whether there is a zero mac address 
(is_zero_ether_addr). But Linus had some ideas when zero mac addresses can be 
useful - maybe he tell us whether it makes sense/problems to have them in the 
translation table.

Kind regards,
	Sven
Antonio Quartulli April 14, 2018, 8:11 a.m. | #3
On 14/04/18 15:10, Sven Eckelmann wrote:
> On Samstag, 14. April 2018 04:34:42 CEST Antonio Quartulli wrote:
>>
>> On 14/04/18 02:16, Sven Eckelmann wrote:
> [...]
>> We already handle the case of multiple originators handling the same MAC
>> address, no? In that case I think we pick the "best" originator.
> 
> Yes, but this doesn't make a lot of sense for multicast and zero mac 
> addresses. The translate layer of batctl is usually used to ping/traceroute to 
> some originator. But multicast and zero mac addresses don't represent a 
> "client" which can be used to identify some originator. So it doesn't seem to 
> make sense to allow them here.

Right.

> 
> Or even without the ping/traceroute stuff, the concept of calling `batctl 
> translate` should give you an answer which you can understand. So it should 
> tell you that batman-adv is very likely to transmit a unicast packet with this 
> destination address to this originator. But this cannot work for multicast 
> destination addresses because multiple answer should be given here - which is 
> out of scope for this command. Which reminds me that I should propose a second 
> patch which checks whether the input for translate_mac is "valid" before 
> trying to translate it.
> 
>> This case sounds more like a validity check because "a zero MAC should
>> not be in the translation table", or am I wrong?
> 
> Partially, yes. I personally don't care (at the moment) whether there is a 
> zero mac address in the translation table. The current translation table code 
> (batadv_tt_local_add) doesn't check whether there is a zero mac address 
> (is_zero_ether_addr). But Linus had some ideas when zero mac addresses can be 
> useful - maybe he tell us whether it makes sense/problems to have them in the 
> translation table.

Yeah, I agree that zero "may appear" in the table and therefore we have
to "check" what we are getting back and whether it makes sense for us in
this context.


Actually my comment was not about changing your approach, but just
making it more explicit in the commit and in the error message.

An error message like like "returned invalid all-zero mac address" (or
"multicast address") might help to distinguish similar "ambiguities" in
the future. No?



Cheers,



> 
> Kind regards,
> 	Sven
>
Sven Eckelmann April 14, 2018, 9:20 a.m. | #4
On Samstag, 14. April 2018 10:11:28 CEST Antonio Quartulli wrote:
> An error message like like "returned invalid all-zero mac address" (or
> "multicast address") might help to distinguish similar "ambiguities" in
> the future. No?

The current interface for the translation is "give me a string and I return 
NULL or a mac address". The resolving of the IPs for hostnames and the check 
of the neighbor table are done on an "I take what I get first" approach. Your 
suggestion would involve a change of this interface and parsing of additional 
information and tracking of states to make sure that the "best" result is 
returned (or a special error state). This is nothing which I will implement 
now.

Should I drop the patch for now?

Kind regards,
	Sven
Antonio Quartulli April 14, 2018, 9:35 a.m. | #5
On 14/04/18 17:20, Sven Eckelmann wrote:
> On Samstag, 14. April 2018 10:11:28 CEST Antonio Quartulli wrote:
>> An error message like like "returned invalid all-zero mac address" (or
>> "multicast address") might help to distinguish similar "ambiguities" in
>> the future. No?
> 
> The current interface for the translation is "give me a string and I return 
> NULL or a mac address". The resolving of the IPs for hostnames and the check 
> of the neighbor table are done on an "I take what I get first" approach. Your 
> suggestion would involve a change of this interface and parsing of additional 
> information and tracking of states to make sure that the "best" result is 
> returned (or a special error state). This is nothing which I will implement 
> now.

Oh ok, I went through the code and now I better understand what you meant.

> 
> Should I drop the patch for now?
> 

I'd suggest to still consider it for merging.
Even if we can't be specific about the error, it is still better to stop
the translation rather than generating unexpected results.

Cheers,
Antonio Quartulli April 14, 2018, 9:36 a.m. | #6
On 14/04/18 02:16, Sven Eckelmann wrote:
> The IP translation layer is using the neighbor table of the kernel to get
> the unicast link layer (mac) address for IP(v4|v6) addresses. The kernel
> can not only return unicast mac addresses to such an RTM_GETNEIGH request
> but also zero mac address. Such an address must be considered invalid
> because the global translation table may not only contain a unique client
> mac address entry for it. The translation from client mac to originator
> will therefore most likely return an unexpected originator.
> 
> Dropping these kind of (bogus) results avoids confusions while using things
> like batctl's ping or traceroute.
> 
> Reported-by: Andre Kasper <Andre.Kasper@gmx.de>
> Signed-off-by: Sven Eckelmann <sven@narfation.org>

Acked-by: Antonio Quartulli <a@unstable.cc>
Sven Eckelmann April 17, 2018, 8:35 a.m. | #7
On Freitag, 13. April 2018 20:16:18 CEST Sven Eckelmann wrote:
> The IP translation layer is using the neighbor table of the kernel to get
> the unicast link layer (mac) address for IP(v4|v6) addresses. The kernel
> can not only return unicast mac addresses to such an RTM_GETNEIGH request
> but also zero mac address. Such an address must be considered invalid
> because the global translation table may not only contain a unique client
> mac address entry for it. The translation from client mac to originator
> will therefore most likely return an unexpected originator.
> 
> Dropping these kind of (bogus) results avoids confusions while using things
> like batctl's ping or traceroute.
> 
> Reported-by: Andre Kasper <Andre.Kasper@gmx.de>
> Signed-off-by: Sven Eckelmann <sven@narfation.org>
> ---
> Cc: Andre Kasper <Andre.Kasper@gmx.de>
> 
> See https://www.open-mesh.org/issues/353

Applied in 9f22e3d0ed2a [1]. But the ticket is not marked as resolved but it 
seems like the reporter wants a different behavior.

Kind regards,
	Sven

[1] https://git.open-mesh.org/batctl.git/commit/9f22e3d0ed2a3d83479f3db3b570f49218024249

Patch

diff --git a/functions.c b/functions.c
index cd92b60..3c340a2 100644
--- a/functions.c
+++ b/functions.c
@@ -571,6 +571,19 @@  static struct nla_policy neigh_policy[NDA_MAX+1] = {
 	[NDA_PROBES]    = { .type = NLA_U32 },
 };
 
+static bool ether_addr_valid(const uint8_t *addr)
+{
+	/* no multicast address */
+	if (addr[0] & 0x01)
+		return false;
+
+	/* no zero address */
+	if ((addr[0] | addr[1] | addr[2] | addr[3] | addr[4] | addr[5]) == 0)
+		return false;
+
+	return true;
+}
+
 static int resolve_mac_from_parse(struct nl_msg *msg, void *arg)
 {
 	struct nlattr *tb[NDA_MAX + 1];
@@ -616,6 +629,9 @@  static int resolve_mac_from_parse(struct nl_msg *msg, void *arg)
 	mac = nla_data(tb[NDA_LLADDR]);
 	l3addr = nla_data(tb[NDA_DST]);
 
+	if (!ether_addr_valid(mac))
+		goto err;
+
 	if (memcmp(nl_arg->l3addr, l3addr, l3_len) == 0) {
 		memcpy(nl_arg->mac_result, mac, ETH_ALEN);
 		nl_arg->found = 1;