linux-kernel - Re: [PATCH 2/2] i2c: Fix a potential use after free

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Message-ID: <20200322155652.GC1091@ninjato>
Date:   Sun, 22 Mar 2020 16:56:52 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Xu Wang <vulab@...as.ac.cn>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] i2c: Fix a potential use after free

On Fri, Dec 27, 2019 at 09:34:32AM +0000, Xu Wang wrote:
> Free the adap structure only after we are done using it.
> This patch just moves the put_device() down a bit to avoid the
> use after free.
> 
> Signed-off-by: Xu Wang <vulab@...as.ac.cn>

Do you have a testcase to reproduce it?

I wonder because we are freeing the device structure which is embedded
inside the adap structure, not the adap structure itself. Or?

> ---
>  drivers/i2c/i2c-core-base.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 9f8dcd3..160d43e 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -2301,8 +2301,8 @@ void i2c_put_adapter(struct i2c_adapter *adap)
>  	if (!adap)
>  		return;
>  
> -	put_device(&adap->dev);
>  	module_put(adap->owner);
> +	put_device(&adap->dev);
>  }
>  EXPORT_SYMBOL(i2c_put_adapter);
>  
> -- 
> 2.7.4
> 

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