net: mctp: copy skb ext data when fragmenting

[ Upstream commit 1394c1dec1c619a46867ed32791a29695372bff8 ]

If we're fragmenting on local output, the original packet may contain
ext data for the MCTP flows. We'll want this in the resulting fragment
skbs too.

So, do a skb_ext_copy() in the fragmentation path, and implement the
MCTP-specific parts of an ext copy operation.

Fixes: 67737c4572 ("mctp: Pass flow data & flow release events to drivers")
Reported-by: Jian Zhang <zhangjian.3032@bytedance.com>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/core/skbuff.c

@@ -6659,6 +6659,14 @@ static struct skb_ext *skb_ext_maybe_cow(struct skb_ext *old,
 		for (i = 0; i < sp->len; i++)
 			xfrm_state_hold(sp->xvec[i]);
 	}
+#endif
+#ifdef CONFIG_MCTP_FLOWS
+	if (old_active & (1 << SKB_EXT_MCTP)) {
+		struct mctp_flow *flow = skb_ext_get_ptr(old, SKB_EXT_MCTP);
+
+		if (flow->key)
+			refcount_inc(&flow->key->refs);
+	}
 #endif
 	__skb_ext_put(old);
 	return new;

net/mctp/route.c

@@ -843,6 +843,9 @@ static int mctp_do_fragment_route(struct mctp_route *rt, struct sk_buff *skb,
 		/* copy message payload */
 		skb_copy_bits(skb, pos, skb_transport_header(skb2), size);
 
+		/* we need to copy the extensions, for MCTP flow data */
+		skb_ext_copy(skb2, skb);
+
 		/* do route */
 		rc = rt->output(rt, skb2);
 		if (rc)