[PATCH net v3 1/3] net: hsr: privatize interlink-bound skbs before address mutation

[Xin Xie <xiexinet@gmail.com>]

An skb sent to a RedBox interlink can share data with master delivery
or the original TX skb. hsr_deliver_master() and hsr_xmit() then write
different source addresses, so one consumer can observe the other's
address.

Use skb_cow() before interlink address substitution when those paths
can share the data. Drop that egress on COW failure. Other interlink
traffic keeps its zero-copy behavior.

Fixes: 5055cccfc2d1 ("net: hsr: Provide RedBox support (HSR-SAN)")
Reviewed-by: Ali Ahmet Memis <ali@iusegentoo.com>
Tested-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Xin Xie <xiexinet@gmail.com>
---
 net/hsr/hsr_forward.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
index 0774981a65c1..67aaf5a8622b 100644
--- a/net/hsr/hsr_forward.c
+++ b/net/hsr/hsr_forward.c
@@ -420,6 +420,22 @@ static void hsr_deliver_master(struct sk_buff *skb, struct net_device *dev,
 static int hsr_xmit(struct sk_buff *skb, struct hsr_port *port,
 		    struct hsr_frame_info *frame)
 {
+	/* An interlink-bound skb from get_untagged_frame() can still alias
+	 * another live consumer: for master-originated frames the clone
+	 * shares the original TX skb (which taps or the TX path may still
+	 * hold); for ring frames the master also consumes them when they
+	 * are destined to the local node without being exclusive to it.
+	 * Privatize before any address mutation.
+	 */
+	if (port->type == HSR_PT_INTERLINK &&
+	    (frame->port_rcv->type == HSR_PT_MASTER ||
+	     (frame->is_local_dest && !frame->is_local_exclusive)) &&
+	    skb_cow(skb, 0)) {
+		frame->port_rcv->dev->stats.rx_dropped++;
+		kfree_skb(skb);
+		return NET_XMIT_DROP;
+	}
+
 	if (frame->port_rcv->type == HSR_PT_MASTER) {
 		hsr_addr_subst_dest(frame->node_src, skb, port);
 
-- 
2.43.0