linux-kernel - Re: [PATCH] ieee802154: ca8210: Fix a potential UAF in ca8210

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Message-ID: <20230925102919.356b45ab@xps-13>
Date:   Mon, 25 Sep 2023 10:29:19 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Dinghao Liu <dinghao.liu@....edu.cn>
Cc:     Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Harry Morris <harrymorris12@...il.com>,
        linux-wpan@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ieee802154: ca8210: Fix a potential UAF in ca8210_probe

Hi Dinghao,

dinghao.liu@....edu.cn wrote on Mon, 25 Sep 2023 15:24:22 +0800:

> If of_clk_add_provider() fails in ca8210_register_ext_clock(),
> it calls clk_unregister() to release priv->clk and returns an
> error. However, the caller ca8210_probe() then calls ca8210_remove(),
> where priv->clk is freed again in ca8210_unregister_ext_clock(). In
> this case, a use-after-free may happen in the second time we call
> clk_unregister().
> 
> Fix this by nulling priv->clk after the first clk_unregister(). Also
> refine the pointer checking in ca8210_unregister_ext_clock().
> 
> Fixes: ded845a781a5 ("ieee802154: Add CA8210 IEEE 802.15.4 device driver")
> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> ---
>  drivers/net/ieee802154/ca8210.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ieee802154/ca8210.c b/drivers/net/ieee802154/ca8210.c
> index aebb19f1b3a4..1d545879c000 100644
> --- a/drivers/net/ieee802154/ca8210.c
> +++ b/drivers/net/ieee802154/ca8210.c
> @@ -2760,6 +2760,7 @@ static int ca8210_register_ext_clock(struct spi_device *spi)
>  	ret = of_clk_add_provider(np, of_clk_src_simple_get, priv->clk);
>  	if (ret) {
>  		clk_unregister(priv->clk);
> +		priv->clk = NULL;

This function is a bit convoluted. You could just return the result of
of_clk_add_provider() (keep the printk's if you want, they don't seem
very useful) and let ca8210_unregister_ext_clock() do the cleanup.

>  		dev_crit(
>  			&spi->dev,
>  			"Failed to register external clock as clock provider\n"
> @@ -2780,7 +2781,7 @@ static void ca8210_unregister_ext_clock(struct spi_device *spi)
>  {
>  	struct ca8210_priv *priv = spi_get_drvdata(spi);
>  
> -	if (!priv->clk)
> +	if (IS_ERR_OR_NULL(priv->clk))

Does not look useful as you are enforcing priv->clock to be valid or
NULL, it cannot be an error code.

Thanks,
Miquèl