linux-kernel - Re: [PATCH 5.10 06/41] net: pxa168_eth: Fix a potential data race in pxa168_eth

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Message-ID: <20210409103355.GA10988@amd>
Date:   Fri, 9 Apr 2021 12:33:55 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Pavel Andrianov <andrianov@...ras.ru>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.10 06/41] net: pxa168_eth: Fix a potential data race in
 pxa168_eth_remove

Hi!

> [ Upstream commit 0571a753cb07982cc82f4a5115e0b321da89e1f3 ]
> 
> pxa168_eth_remove() firstly calls unregister_netdev(),
> then cancels a timeout work. unregister_netdev() shuts down a device
> interface and removes it from the kernel tables. If the timeout occurs
> in parallel, the timeout work (pxa168_eth_tx_timeout_task) performs stop
> and open of the device. It may lead to an inconsistent state and memory
> leaks.

AFAICT the timeout work does a lot of processing, including
pxa168_eth_open(), pxa168_init_phy() and phy_connect_direct(). We
probably don't want that to run with clock being disabled and DMA
being unmapped.

We certainly don't want phy_disconnect() being undone by
phy_connect_direct() running in the workqueue.

IOW this patch is not enough to fix the bugs, and at least fix below
is needed to get something reasonable.

Signed-off-by: Pavel Machek (CIP) <pavel@...x.de>

Best regards,
								Pavel

> +++ b/drivers/net/ethernet/marvell/pxa168_eth.c
> @@ -1544,8 +1544,8 @@ static int pxa168_eth_remove(struct platform_device *pdev)
>  	clk_disable_unprepare(pep->clk);
>  	mdiobus_unregister(pep->smi_bus);
>  	mdiobus_free(pep->smi_bus);
> -	unregister_netdev(dev);
>  	cancel_work_sync(&pep->tx_timeout_task);
> +	unregister_netdev(dev);
>  	free_netdev(dev);
>  	return 0;
>  }

diff --git a/drivers/net/ethernet/marvell/pxa168_eth.c b/drivers/net/ethernet/marvell/pxa168_eth.c
index d1e4d42e497d..432be22a51be 100644
--- a/drivers/net/ethernet/marvell/pxa168_eth.c
+++ b/drivers/net/ethernet/marvell/pxa168_eth.c
@@ -1532,7 +1532,8 @@ static int pxa168_eth_remove(struct platform_device *pdev)
 {
 	struct net_device *dev = platform_get_drvdata(pdev);
 	struct pxa168_eth_private *pep = netdev_priv(dev);
-
+	
+	cancel_work_sync(&pep->tx_timeout_task);
 	if (pep->htpr) {
 		dma_free_coherent(pep->dev->dev.parent, HASH_ADDR_TABLE_SIZE,
 				  pep->htpr, pep->htpr_dma);
@@ -1545,7 +1546,6 @@ static int pxa168_eth_remove(struct platform_device *pdev)
 	mdiobus_unregister(pep->smi_bus);
 	mdiobus_free(pep->smi_bus);
 	unregister_netdev(dev);
-	cancel_work_sync(&pep->tx_timeout_task);
 	free_netdev(dev);
 	return 0;
 }

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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