linux-kernel - [PATCH] micrel: ksz8851: fixes struct pointer issue

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Date:   Mon, 22 Aug 2022 16:39:32 -0500
From:   Jerry Ray <jerry.ray@...rochip.com>
To:     "David S . Miller " <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jerry Ray <jerry.ray@...rochip.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <UNGLinuxDriver@...rochip.com>
Subject: [PATCH] micrel: ksz8851: fixes struct pointer issue

Issue found during code review. This bug has no impact as long as the
ks8851_net structure is the first element of the ks8851_net_spi structure.
As long as the offset to the ks8851_net struct is zero, the container_of()
macro is subtracting 0 and therefore no damage done. But if the
ks8851_net_spi struct is ever modified such that the ks8851_net struct
within it is no longer the first element of the struct, then the bug would
manifest itself and cause problems.

struct ks8851_net is contained within ks8851_net_spi.
ks is contained within kss.
kss is the priv_data of the netdev structure.

Signed-off-by: Jerry Ray <jerry.ray@...rochip.com>
---
 drivers/net/ethernet/micrel/ks8851_spi.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/micrel/ks8851_spi.c b/drivers/net/ethernet/micrel/ks8851_spi.c
index 479406ecbaa3..13c76352ae8d 100644
--- a/drivers/net/ethernet/micrel/ks8851_spi.c
+++ b/drivers/net/ethernet/micrel/ks8851_spi.c
@@ -413,7 +413,8 @@ static int ks8851_probe_spi(struct spi_device *spi)

 	spi->bits_per_word = 8;

-	ks = netdev_priv(netdev);
+	kss = netdev_priv(netdev);
+	ks = &kss->ks8851;

 	ks->lock = ks8851_lock_spi;
 	ks->unlock = ks8851_unlock_spi;
@@ -433,8 +434,6 @@ static int ks8851_probe_spi(struct spi_device *spi)
 		 IRQ_RXPSI)	/* RX process stop */
 	ks->rc_ier = STD_IRQ;

-	kss = to_ks8851_spi(ks);
-
 	kss->spidev = spi;
 	mutex_init(&kss->lock);
 	INIT_WORK(&kss->tx_work, ks8851_tx_work);
-- 
2.17.1