linux-kernel - Re: [PATCH v1] counter: fix NULL pointer dereference on counter_comp_u8

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Message-ID: <YfzPcyusGwAOkys6@shinobu>
Date:   Fri, 4 Feb 2022 16:02:11 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        David Jander <david@...tonic.nl>,
        Robin van der Gracht <robin@...tonic.nl>,
        linux-iio@...r.kernel.org, Jonathan Cameron <jic23@...nel.org>,
        u.kleine-koenig@...gutronix.de
Subject: Re: [PATCH v1] counter: fix NULL pointer dereference on
 counter_comp_u8_store()

On Thu, Feb 03, 2022 at 02:54:18PM +0100, Oleksij Rempel wrote:
> Current kernel will report NULL pointer dereference with following
> back trace:
>   interrupt_cnt_enable_write from counter_comp_u8_store+0xc0/0xf4
>   counter_comp_u8_store from dev_attr_store+0x24/0x30
>   dev_attr_store from sysfs_kf_write+0x48/0x54
>   sysfs_kf_write from kernfs_fop_write_iter+0x128/0x1c8
>   kernfs_fop_write_iter from vfs_write+0x124/0x1b4
>   vfs_write from ksys_write+0x88/0xe0
>   ksys_write from sys_write+0x18/0x1c
>   sys_write from ret_fast_syscall+0x0/0x1c
> 
> Add missing dev_set_drvdata() to fix it.
> 
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>

Hi Oleksij,

This dev_set_drvdata() was removed in commit b56346ddbd82 ("counter: Use
container_of instead of drvdata to track counter_device"). It looks like
we overlooked the counter-sysfs.c file when we made that change.

Would you instead replace the dev_get_drvdata() calls in counter-sysfs.c
with respective container_of() calls? Add a Fixes tag referencing commit
b56346ddbd82 as well to your commit message.

Thanks,

William Breathitt Gray

> ---
>  drivers/counter/counter-core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/counter/counter-core.c b/drivers/counter/counter-core.c
> index 7e0957eea094..1de16d5e9fbc 100644
> --- a/drivers/counter/counter-core.c
> +++ b/drivers/counter/counter-core.c
> @@ -98,6 +98,8 @@ struct counter_device *counter_alloc(size_t sizeof_priv)
>  	counter = &ch->counter;
>  	dev = &counter->dev;
>  
> +	dev_set_drvdata(dev, counter);
> +
>  	/* Acquire unique ID */
>  	err = ida_alloc(&counter_ida, GFP_KERNEL);
>  	if (err < 0)
> -- 
> 2.30.2
> 

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