From b7d78b46d5e8dc77c656c13885d31e931923b915 Mon Sep 17 00:00:00 2001
From: Vladimir Oltean <vladimir.oltean@nxp.com>
Date: Wed, 29 Jun 2022 22:33:58 +0300
Subject: [PATCH] net: phylink: fix NULL pl->pcs dereference during
 phylink_pcs_poll_start

The current link mode of the phylink instance may not require an
attached PCS. However, phylink_major_config() unconditionally
dereferences this potentially NULL pointer when restarting the link poll
timer, which will panic the kernel.

Fix the problem by checking whether a PCS exists in phylink_pcs_poll_start(),
otherwise do nothing. The code prior to the blamed patch also only
looked at pcs->poll within an "if (pcs)" block.

Fixes: bfac8c490d60 ("net: phylink: disable PCS polling over major configuration")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Tested-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Tested-by: Michael Walle <michael@walle.cc> # on kontron-kbox-a-230-ls
Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com> # on sam9x60ek
Link: https://lore.kernel.org/r/20220629193358.4007923-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 drivers/net/phy/phylink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -764,7 +764,7 @@ static void phylink_pcs_poll_stop(struct
 
 static void phylink_pcs_poll_start(struct phylink *pl)
 {
-	if (pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
+	if (pl->pcs && pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
 		mod_timer(&pl->link_poll, jiffies + HZ);
 }
 
