mctp: Implement message fragmentation & reassembly

This change implements MCTP fragmentation (based on route & device MTU),
and corresponding reassembly.

The MCTP specification only allows for fragmentation on the originating
message endpoint, and reassembly on the destination endpoint -
intermediate nodes do not need to reassemble/refragment.  Consequently,
we only fragment in the local transmit path, and reassemble
locally-bound packets. Messages are required to be in-order, so we
simply cancel reassembly on out-of-order or missing packets.

In the fragmentation path, we just break up the message into MTU-sized
fragments; the skb structure is a simple copy for now, which we can later
improve with a shared data implementation.

For reassembly, we keep track of incoming message fragments using the
existing tag infrastructure, allocating a key on the (src,dest,tag)
tuple, and reassembles matching fragments into a skb->frag_list.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 0 deletions

diff --git a/net/mctp/af_mctp.c b/net/mctp/af_mctp.c
index 52bd7f2b78db..9ca836df19d0 100644
--- a/net/mctp/af_mctp.c
+++ b/net/mctp/af_mctp.c
@@ -263,6 +263,14 @@ static void mctp_sk_unhash(struct sock *sk)
 	hlist_for_each_entry_safe(key, tmp, &msk->keys, sklist) {
 		hlist_del_rcu(&key->sklist);
 		hlist_del_rcu(&key->hlist);
+
+		spin_lock(&key->reasm_lock);
+		if (key->reasm_head)
+			kfree_skb(key->reasm_head);
+		key->reasm_head = NULL;
+		key->reasm_dead = true;
+		spin_unlock(&key->reasm_lock);
+
 		kfree_rcu(key, rcu);
 	}
 	spin_unlock_irqrestore(&net->mctp.keys_lock, flags);