Due to some changes to the minimal forwarding draft and in preparation
for Selective Fragment Recovery some changes to the VRB API were
needed. Now the index of a VRB entry is only (L2 src, tag) not as
before (L2 src, L2 dst, length, tag).
I know that the current `rbuf_base` causes waste, as all the fields not
used by the new index are effectively not used by the VRB. I'd like to
fix that however in a later change, since that also requires some
modifications of the classic reassembly buffer, and thus would
complicate the review and testing of the change.
Sources for the index change:
- https://tools.ietf.org/html/draft-ietf-6lo-minimal-fragment-04#section-1
- https://mailarchive.ietf.org/arch/browse/6lo/?gbt=1&index=DLCTxC2X4bRNtYPHhtEkavMWlz4
TCP options have up to three fields (kind, length, value). The
current code only checks for the presence of the first field. Before
accessing the second field (length) the code must ensure that a length
field is even present.
A received packet is outputted in DEBUG _after_ it was already parsed,
but with a reference to the already parsed header. The result is that
there can be some garbage in the output and the packet is not dumped in
total. As without parsing we do not have access to the header yet, we
use the `gnrc_netif_addr_to_str()` helper function instead of parsing
the destination address by hand.
before this commit the src address was checked for multicast, but the dst address should be checked. Therefore udp multicast packets would be flooded back to the src as ICMPv6 error, as not all nodes had a UDP receiver registered.
From the gnrc_pktbuf_mark documentation:
It's not guaranteed that `result->data` points to the
same address as the original `pkt->data.
Thus it should be necessary to update the `hdr` pointer.
If an address was pre-configured by the upper layer its validity is
currently ignored. It is neither checked if the address is on the
interface at all nor is it checked if it is valid.
This change provides a fix for that by checking both facts.
When reworking the reception of IPv6 packets I reset a previously set
`ipv6` snip as follows when the IPv6 extension handler returns a
packet (see first hunk of this commit):
```C
ipv6 = pkt->next->next
```
With `gnrc_ipv6_ext` this makes *somewhat* sense, `pkt->next` was
previously equal to `ipv6` and after the function call `pkt->next`
is the marked extension header, while `pkt->next->next` is the IPv6
header. However, since `ipv6` is already write-protected i.e.
`ipv6->users == 1` (see ll. 665-675), any additional call of
`gnrc_pktbuf_start_write()` [won't][start-write-doc] duplicate the
packet. In fact, the only `gnrc_pktbuf_start_write()` in
`gnrc_ipv6_ext` is used to send the *result* to the subscribers of that
extension header type, leaving the original packet unchanged for the
caller. As such `ipv6` remains the pointer to the IPv6 header whether
we set it in the line above or not. So we actually don't need that
line.
However, the extension header handling also returns a packet when
`gnrc_ipv6_ext` is not compiled in. In that case it is just a dummy
define that returns the packet you give provide it which means that
this still holds true: `pkt->next == ipv6`.
So setting `ipv6` in this case is actually harmful, as `ipv6` now
points to the NETIF header [following the IPv6 header][pkt-structure]
in the packet and this causes the `user` counter of that NETIF header
`hdr` to be decremented if `hdr->users > 1` in the write-protection I
removed in hunk 2 of this commit:
```C
/* pkt might not be writable yet, if header was given above */
ipv6 = gnrc_pktbuf_start_write(ipv6);
if (ipv6 == NULL) {
DEBUG("ipv6: unable to get write access to packet: dropping it\n");
gnrc_pktbuf_release(pkt);
return;
}
```
But as we already established, `ipv6->users` is already 1, so we don't
actually need the write protection here either.
Since the packet stays unchanged after the `ipv6` snip, we also don't
need to re-search for `netif_hdr` after the other two lines are
removed.
[start-write-doc]: https://doc.riot-os.org/group__net__gnrc__pktbuf.html#ga640418467294ae3d408c109ab27bd617
[pkt-structure]: https://doc.riot-os.org/group__net__gnrc__pkt.html#ga278e783e56a5ee6f1bd7b81077ed82a7
The `addr` parameter of the NIB's `_handle_dad()` function can come
from anywhere (e.g. in the fallback to classic SLAAC the destination
address of the IP header is used), so putting that pointer in a timer
is not a good idea. Instead we use the version of the address that is
stored within the interface.
