netdev - [PATCH net-next] net: phylink: fix NULL pl->pcs dereference during phylink_pcs_poll

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Date:   Wed, 29 Jun 2022 22:33:58 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Russell King <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: [PATCH net-next] 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@....com>
---
 drivers/net/phy/phylink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 1a7550f5fdf5..48f0b9b39491 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -766,7 +766,7 @@ static void phylink_pcs_poll_stop(struct phylink *pl)
 
 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);
 }
 
-- 
2.25.1