Re: [PATCH] staging:wlan-ng: use memdup_user instead of kmalloc/copy_from_user

[Dan Carpenter <dan.carpenter@oracle.com>]

On Mon, Feb 15, 2021 at 09:44:24AM +0100, Michal Hocko wrote:
> On Sat 13-02-21 15:05:28, Ivan Safonov wrote:
> > memdup_user() is shorter and safer equivalent
> > of kmalloc/copy_from_user pair.
> > 
> > Signed-off-by: Ivan Safonov <insafonov@gmail.com>
> > ---
> >  drivers/staging/wlan-ng/p80211netdev.c | 28 ++++++++++++--------------
> >  1 file changed, 13 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/staging/wlan-ng/p80211netdev.c b/drivers/staging/wlan-ng/p80211netdev.c
> > index a15abb2c8f54..6f9666dc0277 100644
> > --- a/drivers/staging/wlan-ng/p80211netdev.c
> > +++ b/drivers/staging/wlan-ng/p80211netdev.c
> > @@ -569,24 +569,22 @@ static int p80211knetdev_do_ioctl(struct net_device *dev,
> >  		goto bail;
> >  	}
> >  
> > -	/* Allocate a buf of size req->len */
> > -	msgbuf = kmalloc(req->len, GFP_KERNEL);
> > -	if (msgbuf) {
> > -		if (copy_from_user(msgbuf, (void __user *)req->data, req->len))
> > -			result = -EFAULT;
> > -		else
> > -			result = p80211req_dorequest(wlandev, msgbuf);
> > +	msgbuf = memdup_user(req->data, req->len);
> 
> Move to memdup_user is definitely a right step. What is the range of
> req->len though? If this can be larger than PAGE_SIZE then vmemdup_user
> would be a better alternative.

req->len shoudn't be anywhere close to PAGE_SIZE but it's actually
important to check req->len and this code does not do that which leads
to memory corruption:

drivers/staging/wlan-ng/p80211netdev.c
   566                  goto bail;
   567          } else if (cmd != P80211_IFREQ) {
   568                  result = -EINVAL;
   569                  goto bail;
   570          }
   571  
   572          msgbuf = memdup_user(req->data, req->len);
   573          if (IS_ERR(msgbuf)) {
   574                  result = PTR_ERR(msgbuf);
   575                  goto bail;
   576          }
   577  
   578          result = p80211req_dorequest(wlandev, msgbuf);

We don't know that "req->len" is >= sizeof(*msgbuf), and then we pass
msgbuf top80211req_dorequest() which calls p80211req_handlemsg().  In
p80211req_handlemsg() then "req->len" has to be larger than
sizeof(struct p80211msg_lnxreq_hostwep).

   579  
   580          if (result == 0) {
   581                  if (copy_to_user
   582                      ((void __user *)req->data, msgbuf, req->len)) {
   583                          result = -EFAULT;
   584                  }
   585          }
   586          kfree(msgbuf);
   587  
   588  bail:
   589          /* If allocate,copyfrom or copyto fails, return errno */
   590          return result;
   591  }

Smatch has a problem parsing this code because struct ifreq *ifr is a
union and Smatch gets confused.  :/

regards,
dan carpenter