linux-kernel - Re: [PATCH] staging: wlan-ng/p80211 : check userspacebuf size for sanity

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Message-ID: <YDPKL47kPVyRPRcC@karthik-strix-linux.karthek.com>
Date:   Mon, 22 Feb 2021 20:43:51 +0530
From:   karthek <mail@...thek.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org
Subject: Re: [PATCH] staging: wlan-ng/p80211 : check userspacebuf size for
 sanity

On Mon, Feb 22, 2021 at 04:59:37PM +0300, Dan Carpenter wrote:
> I have added the Driver Devel list to the CC list.  Adding linux-kernel
> is sort of useless.  The correct people who are interested in this patch
> are all on the Driver Devel list.
> 
> On Mon, Feb 22, 2021 at 07:12:22PM +0530, karthek wrote:
> > On Mon, Feb 22, 2021 at 04:21:33PM +0300, Dan Carpenter wrote:
> > > On Mon, Feb 22, 2021 at 06:16:24PM +0530, karthek wrote:
> > > > currently p80211knetdev_do_ioctl() is testing user passed
> > > > struct ifreq for sanity by checking for presence of a magic number,
> > > > in addition to that also check size field, preventing buffer overflow
> > > > before passing data to p80211req_dorequest() which casts it
> > > > to *struct p80211msg
> > > > 
> > > > Signed-off-by: karthek <mail@...thek.com>
> > > > ---
> > > > is this correct?
> > > > is it necessary to check for size in addition to magicnum?
> > > > did i even understand the problem correctly?
> > > > 
> > > >  drivers/staging/wlan-ng/p80211netdev.c | 5 ++++-
> > > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/staging/wlan-ng/p80211netdev.c b/drivers/staging/wlan-ng/p80211netdev.c
> > > > index 70570e8a5..c7b78d870 100644
> > > > --- a/drivers/staging/wlan-ng/p80211netdev.c
> > > > +++ b/drivers/staging/wlan-ng/p80211netdev.c
> > > > @@ -568,7 +568,10 @@ static int p80211knetdev_do_ioctl(struct net_device *dev,
> > > >  		result = -EINVAL;
> > > >  		goto bail;
> > > >  	}
> > > > -
> > > > +	if (req->len < sizeof(struct p80211msg)) {
> > > > +		result = -EINVAL;
> > > > +		goto bail;
> > > > +	}
> > > 
> > > Please don't send private emails.  Always CC the list.
> > sorry
> > > 
> > > That's only a partial solution.  You need to check in p80211req_handlemsg()
> > > as well and probably other places.
> > currently p80211req_handlemsg() is only referenced in p80211req_dorequest()
> > can we check that there instead?
> 
> If I have to do all the work in finding the buffer overflows, then I
> should write my own patch.  :/
> 
> Anyway the p80211knetdev_do_ioctl() function calls p80211req_dorequest()
> which calls p80211req_handlemsg(wlandev, msg); and
> wlandev->mlmerequest(wlandev, msg);.
> 
> We have already discussed the p80211req_handlemsg() function.  The
> wlandev->mlmerequest() function is always just prism2sta_mlmerequest().
> The prism2sta_mlmerequest() calls a bunch of functions and each of those
> functions need to have a different limit check added to prevent memory
> corruption.
> 
> Homework #1: Should we get rid of the wlandev->mlmerequest() pointer
> and just call prism2sta_mlmerequest() directly?
yeah
> 
> Homework #2: Another solution is to just delete all these custom IOCTLs.
> I don't know what they do so I don't know if they are necessary or not.
i wish i could
> 
> regards,
> dan carpenter
>