linux-kernel - Re: [PATCH] i2c: core: fix potential use-after-free on adapter removal

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Message-ID: <YqjlZuFGl0dAUZyd@shikoro>
Date:   Tue, 14 Jun 2022 21:45:42 +0200
From:   Wolfram Sang <wsa@...nel.org>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: core: fix potential use-after-free on adapter
 removal

Hi Michał,

I finally had a look at your patch...

> put_device(&adap->dev) might free the memory pointed to by `adap`,
> so we shouldn't read adap->owner after that.
> 
> Fix by saving module pointer before calling put_device().

... and found a different approach for this problem from 2019:

http://patchwork.ozlabs.org/project/linux-i2c/patch/1577439272-10362-1-git-send-email-vulab@iscas.ac.cn/

I think this is also proper. I found other subsystems in the kernel
first putting the module, then the device. Do you see problems with the
above patch?

Thanks for looking into the issue!

   Wolfram

> 
> Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> ---
>  drivers/i2c/i2c-core-base.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 2c59dd748a49..5d694f8ce9ef 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -2464,11 +2464,14 @@ EXPORT_SYMBOL(i2c_get_adapter);
>  
>  void i2c_put_adapter(struct i2c_adapter *adap)
>  {
> +	struct module *owner;
> +
>  	if (!adap)
>  		return;
>  
> +	owner = adap->owner;
>  	put_device(&adap->dev);
> -	module_put(adap->owner);
> +	module_put(owner);
>  }
>  EXPORT_SYMBOL(i2c_put_adapter);
>  
> -- 
> 2.30.2
> 

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