net: hsr: Use the seqnr lock for frames received via interlink port.

syzbot reported that the seqnr_lock is not acquire for frames received
over the interlink port. In the interlink case a new seqnr is generated
and assigned to the frame.
Frames, which are received over the slave port have already a sequence
number assigned so the lock is not required.

Acquire the hsr_priv::seqnr_lock during in the invocation of
hsr_forward_skb() if a packet has been received from the interlink port.

Reported-by: syzbot+3d602af7549af539274e@syzkaller.appspotmail.com
Closes: https://groups.google.com/g/syzkaller-bugs/c/KppVvGviGg4/m/EItSdCZdBAAJ
Fixes: 5055ccc ("net: hsr: Provide RedBox support (HSR-SAN)")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Tested-by: Lukasz Majewski <lukma@denx.de>
Link: https://patch.msgid.link/20240906132816.657485-2-bigeasy@linutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/hsr/hsr_slave.c

@@ -67,7 +67,16 @@ static rx_handler_result_t hsr_handle_frame(struct sk_buff **pskb)
 		skb_set_network_header(skb, ETH_HLEN + HSR_HLEN);
 	skb_reset_mac_len(skb);
 
-	hsr_forward_skb(skb, port);
+	/* Only the frames received over the interlink port will assign a
+	 * sequence number and require synchronisation vs other sender.
+	 */
+	if (port->type == HSR_PT_INTERLINK) {
+		spin_lock_bh(&hsr->seqnr_lock);
+		hsr_forward_skb(skb, port);
+		spin_unlock_bh(&hsr->seqnr_lock);
+	} else {
+		hsr_forward_skb(skb, port);
+	}
 
 finish_consume:
 	return RX_HANDLER_CONSUMED;