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

Palmer Dabbelt
2020-01-22T23:56:08Z

On Fri, 03 Jan 2020 16:19:21 PST (-0800), sboyd@kernel.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@microchip.com>
> Cc: Yash Shah <yash.shah@sifive.com>
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Fixes: c218ad559020 ("macb: Add support for SiFive FU540-C000")
> Signed-off-by: Stephen Boyd <sboyd@kernel.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@google.com>

Thanks!