Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Charlie Sands <sandsch@northvilleschools.net>,
        Dan Carpenter <dan.carpenter@oracle.com>
Cc:     gregkh@linuxfoundation.org, Larry.Finger@lwfinger.net,
        phil@philpotter.co.uk, linux-staging@lists.linux.dev,
        linux-kernel@vger.kernel.org, paskripkin@gmail.com
Subject: Re: [PATCH V2] Fix unsafe memory access by memcmp
Date:   Mon, 04 Apr 2022 13:25:37 +0200
Message-ID: <4729027.31r3eYUQgx@leap>
In-Reply-To: <20220404105041.GX3293@kadam>
References: <YkpdVyuQguGzPSNE@sckzor-linux.localdomain> <20220404105041.GX3293@kadam>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
Precedence: bulk

On luned? 4 aprile 2022 12:50:41 CEST Dan Carpenter wrote:
> On Sun, Apr 03, 2022 at 10:52:07PM -0400, Charlie Sands wrote:
> > This patch fixes sparse warnings about the memcmp function unsafely
> > accessing userspace memory without first copying it to kernel space.
> > 
> > Signed-off-by: Charlie Sands <sandsch@northvilleschools.net>
> > ---
> > 
> > V2: Fixed checkpatch.pl warning and changed variable name as suggested
> > by Greg K. H. and improved error checking on the "copy_from_user" function as
> > suggested by Pavel Skripkin.
> > 
> >  drivers/staging/r8188eu/os_dep/ioctl_linux.c | 21 ++++++++++++--------
> >  1 file changed, 13 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/staging/r8188eu/os_dep/ioctl_linux.c b/drivers/staging/r8188eu/os_dep/ioctl_linux.c
> > index 7df213856d66..4b4eec2bde96 100644
> > --- a/drivers/staging/r8188eu/os_dep/ioctl_linux.c
> > +++ b/drivers/staging/r8188eu/os_dep/ioctl_linux.c
> > @@ -3233,23 +3233,28 @@ static int rtw_p2p_get(struct net_device *dev,
> >  			       struct iw_request_info *info,
> >  			       union iwreq_data *wrqu, char *extra)
> >  {
> > -	if (!memcmp(wrqu->data.pointer, "status", 6)) {
> > +	char wrqu_data[9];
> > +
> > +	if (copy_from_user(wrqu_data, wrqu->data.pointer, 9) != 0)
> > +		return 0;
> 
> return -EFAULT;  We can't assume that that user wants to copy 9 bytes
> especially when they're passing a 4 character + NUL string.
> 
> This is a custom ioctl.  Called from ioctl_private_iw_point().
> 
> I think if you try to dereference a user pointer like this then it will
> cause a crash, right?  So that means no one has ever tested or used this
> code and we hopefully we can just delete it?

After a quick look, I'm pretty confident that we can also delete 
rtw_p2p_get2() and rtw_p2p_set() unless I'm overlooking something.

Thanks,

Fabio M. De Francesco