Hi, On 07/13/2016 01:15 PM, Jukka Rissanen wrote: > Hi Alex, > > On Tue, 2016-07-12 at 22:34 +0200, Alexander Aring wrote: >> Hi, >> >> On 07/11/2016 09:50 PM, Alexander Aring wrote: >>> >>> These flags should be all the same for 6LoWPAN so move it to >>> 6LoWPAN generic. >>> >>> Signed-off-by: Alexander Aring <aar@xxxxxxxxxxxxxx> >>> --- >>> net/6lowpan/core.c | 1 + >>> net/ieee802154/6lowpan/core.c | 1 - >>> 2 files changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/net/6lowpan/core.c b/net/6lowpan/core.c >>> index a978000..6b7de14 100644 >>> --- a/net/6lowpan/core.c >>> +++ b/net/6lowpan/core.c >>> @@ -62,6 +62,7 @@ int lowpan_register_netdevice(struct net_device >>> *dev, >>> dev->type = ARPHRD_6LOWPAN; >>> dev->mtu = IPV6_MIN_MTU; >>> dev->priv_flags |= IFF_NO_QUEUE; >>> + dev->flags = IFF_BROADCAST | IFF_MULTICAST; >>> >>> dev->header_ops = &header_ops; >>> >>> diff --git a/net/ieee802154/6lowpan/core.c >>> b/net/ieee802154/6lowpan/core.c >>> index 228a711..a60abad 100644 >>> --- a/net/ieee802154/6lowpan/core.c >>> +++ b/net/ieee802154/6lowpan/core.c >>> @@ -92,7 +92,6 @@ static void lowpan_setup(struct net_device *ldev) >>> memset(ldev->broadcast, 0xff, IEEE802154_ADDR_LEN); >>> /* We need an ipv6hdr as minimum len when calling xmit */ >>> ldev->hard_header_len = sizeof(struct ipv6hdr); >> This should be moved to generic 6lowpan as well. >> >> This says at least, the skb->len at xmit callback must be at least a >> length of "sizeof(struct ipv6hdr)" which should be correct. >> >> BUT... >> >> I still have (more than years) the use-case that somebody sends an >> AF_PACKET raw socket over lowpan interface. > > According to packet(7), the "Packet sockets are used to receive or send > raw packets at the device driver (OSI Layer 2) level." > But lowpan0 interface is meant to compress IPv6 header so it is working > on L3 data (or more precisely between L2 and L3). > So I am wondering how this is suppose to work and what kind of use case > you have for this? > I think the issue is more complex, forget what the man page says here. We use this callback for something which isn't made for, because the IPv6 ndisc will tell us over this callback "what's the destination L2 address". Sorry, I wrote something here which confused you. I meant more I think about the use-case that users could try to using AF_PACKET RAW sockets here and I think they can kill the kernel with the right parameters. Sending AF_PACKET RAW here makes completely no sense and should be disabled. Because we set in this callback something in the skb_headroom and xmit callback will use it. IMPORTANT NOTE: this handling is weird, because we except here that between header_create and xmit the IPv6 subsytem will not do skb_put/skb_push anymore. I currently think they will never do that because the header_create callback is normally there to put a mac header to the socket buffer. So IPv6 creation should be mostly done. Sending DGRAM sockets it could make sense somehow for a crazy use-case which maybe under 0.1% users wants. You can give the ndisc information from userspace over that, source and destination address. Nevertheless I would disable AF_PACKET DGRAM/RAW handling, EXCEPT RAW RECEIVE handling. This will already be used by wireshark/tcpdump/etc. --- Alternative half solution: I already thought about to simple make a re-lookup on ipv6 ndisc cache for L3 destination address. Like we do for short address handling. But this will not work for broadcast addresses, I would more use the normally functionality in IPv6 to tell us the L2 destination address which is "header_create". I need to think about the real solution to handle everything, you could also except that somebody sends IPv6 raw over AF_PACKET here, then parsing L3 daddr and do such lookup on ndisc for L2 daddr, but there exists this problem with broadcast. I need to look into IPv6 how we otherwise can detect unicast or multicast, maybe it's just when L3 is multicast, but I would not bet on that. I need to look into IPv6 to get an answer. --- The reason why it should be removed is also below: >> >> I didn't test it yet, but I think this is a simple way to crash the >> kernel on all lowpan interfaces. I currently not sure if I can break >> something there, but I am sure it will send garbage data. >> >> The xmit callback needs data which is available in skb_headroom, this >> data is set by header_create callback which will not called on >> AF_PACKET >> RAW sockets. >> >> The root of this issue is that we don't have L2 here for creating mac >> headers. The header_create callback should do that, but we do 6LoWPAN >> adaptation here and the header_create callback will be used by ndisc >> to >> say "here are the addresses, generate a mac header" and AF_PACKET >> _DGRAM_ (for putting mac header in front of AF_PACKET payload). >> >> We use this callback for the first use-case of ndisc only. >> >> AF_PACKET RAW receive make sense, because tcpdump/wireshark needs to >> capture data. Sending AF_PACKET RAW makes no sense and will I suppose >> crash the kernel and I think every user can do that. >> >> DGRAM sockets maybe makes sense, but I would disable that also for >> (receive and transmit). You need to use PF_INET6 socket types for >> lowpan >> interfaces only. That issue is somehow described at [0]. >> - Alex -- To unsubscribe from this list: send the line "unsubscribe linux-wpan" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
