linux-kernel - Re: [PATCH] fsi: Aspeed: Fix a potential double free

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Message-ID: <YcldM9sgYdjMYMtH@kroah.com>
Date:   Mon, 27 Dec 2021 07:29:07 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     jk@...abs.org, joel@....id.au, alistair@...ple.id.au,
        eajames@...ux.ibm.com, andrew@...id.au, linux-fsi@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] fsi: Aspeed: Fix a potential double free

On Sun, Dec 26, 2021 at 05:56:02PM +0100, Christophe JAILLET wrote:
> 'aspeed' is a devm_alloc'ed, so there is no need to free it explicitly or
> there will be a double free().

A struct device can never be devm_alloced for obvious reasons.  Perhaps
that is the real problem here?

> Remove the 'release' function that is wrong and unneeded.
> 
> Fixes: 606397d67f41 ("fsi: Add ast2600 master driver")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> This patch is completely theoretical. It looks good to me, but there is a
> little too much indirections for me. I'm also not that familiar with
> fixing issue related to 'release' function...
> 
> ... So review with care :)
> ---
>  drivers/fsi/fsi-master-aspeed.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/drivers/fsi/fsi-master-aspeed.c b/drivers/fsi/fsi-master-aspeed.c
> index 8606e55c1721..4a745ccb60cf 100644
> --- a/drivers/fsi/fsi-master-aspeed.c
> +++ b/drivers/fsi/fsi-master-aspeed.c
> @@ -373,14 +373,6 @@ static int aspeed_master_break(struct fsi_master *master, int link)
>  	return aspeed_master_write(master, link, 0, addr, &cmd, 4);
>  }
>  
> -static void aspeed_master_release(struct device *dev)
> -{
> -	struct fsi_master_aspeed *aspeed =
> -		to_fsi_master_aspeed(dev_to_fsi_master(dev));
> -
> -	kfree(aspeed);
> -}
> -
>  /* mmode encoders */
>  static inline u32 fsi_mmode_crs0(u32 x)
>  {
> @@ -603,7 +595,6 @@ static int fsi_master_aspeed_probe(struct platform_device *pdev)
>  	dev_info(&pdev->dev, "hub version %08x (%d links)\n", reg, links);
>  
>  	aspeed->master.dev.parent = &pdev->dev;
> -	aspeed->master.dev.release = aspeed_master_release;

Odd, then what deletes this device structure when the release function
wants to be called?  You should have gotten a big warning from the
kernel when removing the device from the system at runtime, did you test
this somehow?

This does not look correct at all.

greg k-h