linux-kernel - Re: [PATCH] Input: synaptics-rmi4 - Really fix attn

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Message-ID: <20200428011134.GV125362@dtor-ws>
Date:   Mon, 27 Apr 2020 18:11:34 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Evan Green <evgreen@...omium.org>
Cc:     stable@...r.kernel.org,
        Nick Desaulniers <nick.desaulniers@...il.com>,
        Allison Randal <allison@...utok.net>,
        Andrew Duggan <aduggan@...aptics.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Enrico Weigelt <info@...ux.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: synaptics-rmi4 - Really fix attn_data
 use-after-free

On Mon, Apr 27, 2020 at 02:55:48PM -0700, Evan Green wrote:
> Fix a use-after-free noticed by running with KASAN enabled. If
> rmi_irq_fn() is run twice in a row, then rmi_f11_attention() (among
> others) will end up reading from drvdata->attn_data.data, which was
> freed and left dangling in rmi_irq_fn().
> 
> Commit 55edde9fff1a ("Input: synaptics-rmi4 - prevent UAF reported by
> KASAN") correctly identified and analyzed this bug. However the attempted
> fix only NULLed out a local variable, missing the fact that
> drvdata->attn_data is a struct, not a pointer.
> 
> NULL out the correct pointer in the driver data to prevent the attention
> functions from copying from it.
> 
> Fixes: 55edde9fff1a ("Input: synaptics-rmi4 - prevent UAF reported by KASAN")
> Fixes: b908d3cd812a ("Input: synaptics-rmi4 - allow to add attention data")
> 
> Signed-off-by: Evan Green <evgreen@...omium.org>
> 
> Cc: stable@...r.kernel.org
> Cc: Nick Desaulniers <nick.desaulniers@...il.com>

Ugh, this is all kind of ugly, but I guess that's what we have now.
Applied, thank you.

> ---
> 
>  drivers/input/rmi4/rmi_driver.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/input/rmi4/rmi_driver.c b/drivers/input/rmi4/rmi_driver.c
> index 190b9974526bb..c18e1a25bca6e 100644
> --- a/drivers/input/rmi4/rmi_driver.c
> +++ b/drivers/input/rmi4/rmi_driver.c
> @@ -205,7 +205,7 @@ static irqreturn_t rmi_irq_fn(int irq, void *dev_id)
>  
>  	if (count) {
>  		kfree(attn_data.data);
> -		attn_data.data = NULL;
> +		drvdata->attn_data.data = NULL;
>  	}
>  
>  	if (!kfifo_is_empty(&drvdata->attn_fifo))
> -- 
> 2.24.1
> 

-- 
Dmitry