linux-kernel - Re: [PATCH v2] mtd: spi-nor: fix memory leak when using debugfs

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Date:   Wed, 8 Feb 2023 15:12:32 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Michael Walle <michael@...le.cc>
Cc:     linux-kernel@...r.kernel.org,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Pratyush Yadav <pratyush@...nel.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-mtd@...ts.infradead.org, stable <stable@...nel.org>
Subject: Re: [PATCH v2] mtd: spi-nor: fix memory leak when using
 debugfs_lookup()

On Wed, Feb 08, 2023 at 02:36:23PM +0100, Michael Walle wrote:
> Am 2023-02-08 13:57, schrieb Greg Kroah-Hartman:
> > When calling debugfs_lookup() the result must have dput() called on it,
> > otherwise the memory will leak over time.
> > 
> > Cc: Tudor Ambarus <tudor.ambarus@...rochip.com>
> > Cc: Pratyush Yadav <pratyush@...nel.org>
> > Cc: Michael Walle <michael@...le.cc>
> > Cc: Miquel Raynal <miquel.raynal@...tlin.com>
> > Cc: Richard Weinberger <richard@....at>
> > Cc: Vignesh Raghavendra <vigneshr@...com>
> > Cc: linux-mtd@...ts.infradead.org
> > Cc: stable <stable@...nel.org>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > ---
> > v2: fix up to work when module is removed and added, making the fix
> >     much simpler.
> > 
> >  drivers/mtd/spi-nor/debugfs.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/mtd/spi-nor/debugfs.c
> > b/drivers/mtd/spi-nor/debugfs.c
> > index ff895f6758ea..af41fbc09a97 100644
> > --- a/drivers/mtd/spi-nor/debugfs.c
> > +++ b/drivers/mtd/spi-nor/debugfs.c
> > @@ -242,6 +242,7 @@ void spi_nor_debugfs_register(struct spi_nor *nor)
> > 
> >  	d = debugfs_create_dir(dev_name(nor->dev), rootdir);
> >  	nor->debugfs_root = d;
> > +	dput(rootdir);
> 
> rootdir might either be the return value of debugfs_lookup() or
> debugfs_create_dir(). dput() is probably wrong for the latter,
> right? Also there is an early return, where the dput() is missing,
> too.

{sigh}

Yeah, this is all wrong, sorry.  Let me fix this up again, properly.
And to do it properly, let's have the module remove the directory if it
is unloaded, like a good module should :)

greg k-h