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

[Christophe JAILLET]

Le 27/12/2021 à 07:29, Greg KH a écrit :
> 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?

Thanks for the feed-back.

This goes beyond my knowledge of how this should work.
As I can not test myself, I won't be of any help.
I'll let you or anyone else check if something needs to be fixed, and 
how to fix it properly.

Just take my patch as a "Hey! Looks strange to have a kfree() in a 
driver that only call devm_kzalloc() to allocate memory. S.o. should 
give a deeper look at it". :)

CJ

> > Remove the 'release' function that is wrong and unneeded.
> >
> > Fixes: 606397d67f41 ("fsi: Add ast2600 master driver")
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> > ---
> > 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