netdev - Re: [PATCH] macb: Don't unregister clks unconditionally

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Date:   Wed, 22 Jan 2020 15:56:05 -0800 (PST)
From:   Palmer Dabbelt <palmerdabbelt@...gle.com>
To:     sboyd@...nel.org
CC:     davem@...emloft.net, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, nicolas.ferre@...rochip.com,
        yash.shah@...ive.com, linux@...ck-us.net
Subject:     Re: [PATCH] macb: Don't unregister clks unconditionally

On Fri, 03 Jan 2020 16:19:21 PST (-0800), sboyd@...nel.org wrote:
> The only clk init function in this driver that register a clk is
> fu540_c000_clk_init(), and thus we need to unregister the clk when this
> driver is removed on that platform. Other init functions, for example
> macb_clk_init(), don't register clks and therefore we shouldn't
> unregister the clks when this driver is removed. Convert this
> registration path to devm so it gets auto-unregistered when this driver
> is removed and drop the clk_unregister() calls in driver remove (and
> error paths) so that we don't erroneously remove a clk from the system
> that isn't registered by this driver.
>
> Otherwise we get strange crashes with a use-after-free when the
> devm_clk_get() call in macb_clk_init() calls clk_put() on a clk pointer
> that has become invalid because it is freed in clk_unregister().
>
> Cc: Nicolas Ferre <nicolas.ferre@...rochip.com>
> Cc: Yash Shah <yash.shah@...ive.com>
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Fixes: c218ad559020 ("macb: Add support for SiFive FU540-C000")
> Signed-off-by: Stephen Boyd <sboyd@...nel.org>
> ---
>  drivers/net/ethernet/cadence/macb_main.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 9c767ee252ac..7dce403fd27c 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -4069,7 +4069,7 @@ static int fu540_c000_clk_init(struct platform_device *pdev, struct clk **pclk,
>  	mgmt->rate = 0;
>  	mgmt->hw.init = &init;
>
> -	*tx_clk = clk_register(NULL, &mgmt->hw);
> +	*tx_clk = devm_clk_register(&pdev->dev, &mgmt->hw);
>  	if (IS_ERR(*tx_clk))
>  		return PTR_ERR(*tx_clk);
>
> @@ -4397,7 +4397,6 @@ static int macb_probe(struct platform_device *pdev)
>
>  err_disable_clocks:
>  	clk_disable_unprepare(tx_clk);
> -	clk_unregister(tx_clk);
>  	clk_disable_unprepare(hclk);
>  	clk_disable_unprepare(pclk);
>  	clk_disable_unprepare(rx_clk);
> @@ -4427,7 +4426,6 @@ static int macb_remove(struct platform_device *pdev)
>  		pm_runtime_dont_use_autosuspend(&pdev->dev);
>  		if (!pm_runtime_suspended(&pdev->dev)) {
>  			clk_disable_unprepare(bp->tx_clk);
> -			clk_unregister(bp->tx_clk);
>  			clk_disable_unprepare(bp->hclk);
>  			clk_disable_unprepare(bp->pclk);
>  			clk_disable_unprepare(bp->rx_clk);

Reviewed-by: Palmer Dabbelt <palmerdabbelt@...gle.com>

Thanks!