Received-SPF: pass (google.com: domain of linux-kernel+bounces-39634-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
From: "Seunghui Lee" <sh043.lee@samsung.com>
To: "'Greg KH'" <gregkh@linuxfoundation.org>
Cc: <linux-mmc@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<ulf.hansson@linaro.org>, <avri.altman@wdc.com>, <grant.jung@samsung.com>,
	<jt77.jang@samsung.com>, <dh0421.hwang@samsung.com>,
	<junwoo80.lee@samsung.com>, <jangsub.yi@samsung.com>,
	<cw9316.lee@samsung.com>, <sh8267.baek@samsung.com>, <wkon.kim@samsung.com>
In-Reply-To: <2024011945-studio-smitten-300e@gregkh>
Subject: RE: [PATCH] mmc: core: Fix null pointer dereference in bus_shutdown
Date: Fri, 26 Jan 2024 14:16:57 +0900
Message-ID: <011a01da5016$e23f41f0$a6bdc5d0$@samsung.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset="Windows-1252"
Content-Transfer-Encoding: 7bit
Thread-Index: AQGcsgXp9LDtdNDOGMR+ItI0KSVqWgF7z+l9ASFv/iSxTS4YIA==
Content-Language: ko
CMS-TYPE: 101P
DLP-Filter: Pass
References: <CGME20240119073011epcas1p1841e79c8f673c3c69ef696edc9eb47b0@epcas1p1.samsung.com>
	<20240119073247.7441-1-sh043.lee@samsung.com>
	<2024011945-studio-smitten-300e@gregkh>

> -----Original Message-----
> From: Greg KH <gregkh@linuxfoundation.org>
> Sent: Friday, January 19, 2024 5:21 PM
> To: Seunghui Lee <sh043.lee@samsung.com>
> Cc: linux-mmc@vger.kernel.org; linux-kernel@vger.kernel.org;
> ulf.hansson@linaro.org; avri.altman@wdc.com; grant.jung@samsung.com;
> jt77.jang@samsung.com; dh0421.hwang@samsung.com; junwoo80.lee@samsung.com;
> jangsub.yi@samsung.com; cw9316.lee@samsung.com; sh8267.baek@samsung.com;
> wkon.kim@samsung.com
> Subject: Re: [PATCH] mmc: core: Fix null pointer dereference in
> bus_shutdown
> 
> On Fri, Jan 19, 2024 at 04:32:47PM +0900, Seunghui Lee wrote:
> > When shutting down removable device,
> > it can be occurred null pointer dereference.
> 
> How?
> 
> And please wrap your lines properly.
> 
> > To prevent null pointer dereference,
> > At first, check null pointer.
> > Next, block rescan worker to scan removable device during shutdown.
> 
> Why do two things?
> 
> >
> > Signed-off-by: Seunghui Lee <sh043.lee@samsung.com>
> > ---
> >  drivers/mmc/core/bus.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/core/bus.c b/drivers/mmc/core/bus.c index
> > 0af96548e7da..4f370a6577aa 100644
> > --- a/drivers/mmc/core/bus.c
> > +++ b/drivers/mmc/core/bus.c
> > @@ -143,9 +143,17 @@ static void mmc_bus_shutdown(struct device *dev)
> > {
> >  	struct mmc_driver *drv = to_mmc_driver(dev->driver);
> >  	struct mmc_card *card = mmc_dev_to_card(dev);
> > -	struct mmc_host *host = card->host;
> > +	struct mmc_host *host;
> >  	int ret;
> >
> > +	if (!drv || !card) {
> > +		pr_debug("%s: drv or card is NULL.\n", dev_name(dev));
> 
> What is this going to help with?  And why not use dev_dbg()?
> 
> How can drv ever be NULL?  That looks impossible to me based on just the
> code shown here.
> 
> > +		return;
> > +	}
> > +
> > +	host = card->host;
> 
> Why is this change needed?  This line can go back to the top just fine,
> right?
> 
> > +	host->rescan_disable = 1;
> 
> Shouldn't this be a separate change?  And what happens if the check for
> this is right before you set it?  Where is the locking to prevent the
> issue you are attempting to solve?
> 
> thanks,
> 
> greg k-h

I've checked the issue again.
This patch is not the proper solution.
I'll reject this patch.
Hi, Thank you for your comment.