[PATCH net] net: phy: fix race in genphy_update_link

[PATCH net] net: phy: fix race in genphy_update_link

[Heiner Kallweit]

In phy_start_aneg() autoneg is started, and immediately after that
link and autoneg status are read. As reported in [0] it can happen that
at time of this read the PHY has reset the "aneg complete" bit but not
yet the "link up" bit, what can result in a false link-up detection.
To fix this don't report link as up if we're in aneg mode and PHY
doesn't signal "aneg complete".

[0] https://marc.info/?t=156413509900003&r=1&w=2

Fixes: 4950c2ba49cc ("net: phy: fix autoneg mismatch case in genphy_read_status")
Reported-by: liuyonglong <liuyonglong@huawei.com>
Tested-by: liuyonglong <liuyonglong@huawei.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 drivers/net/phy/phy_device.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 6b5cb87f3..7ddd91df9 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1774,6 +1774,12 @@ int genphy_update_link(struct phy_device *phydev)
 	phydev->link = status & BMSR_LSTATUS ? 1 : 0;
 	phydev->autoneg_complete = status & BMSR_ANEGCOMPLETE ? 1 : 0;
 
+	/* Consider the case that autoneg was started and "aneg complete"
+	 * bit has been reset, but "link up" bit not yet.
+	 */
+	if (phydev->autoneg == AUTONEG_ENABLE && !phydev->autoneg_complete)
+		phydev->link = 0;
+
 	return 0;
 }
 EXPORT_SYMBOL(genphy_update_link);
-- 
2.22.0

Re: [PATCH net] net: phy: fix race in genphy_update_link

[David Miller]

From: Heiner Kallweit <hkallweit1@gmail.com>
Date: Wed, 31 Jul 2019 23:05:10 +0200

> In phy_start_aneg() autoneg is started, and immediately after that
> link and autoneg status are read. As reported in [0] it can happen that
> at time of this read the PHY has reset the "aneg complete" bit but not
> yet the "link up" bit, what can result in a false link-up detection.
> To fix this don't report link as up if we're in aneg mode and PHY
> doesn't signal "aneg complete".
> 
> [0] https://marc.info/?t=156413509900003&r=1&w=2
> 
> Fixes: 4950c2ba49cc ("net: phy: fix autoneg mismatch case in genphy_read_status")
> Reported-by: liuyonglong <liuyonglong@huawei.com>
> Tested-by: liuyonglong <liuyonglong@huawei.com>
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>

Applied.