netdev - Re: [patch] tun: signedness bug in tun_get

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Message-ID: <20130815150214.GB8889@redhat.com>
Date:	Thu, 15 Aug 2013 18:02:14 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Jason Wang <jasowang@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Neil Horman <nhorman@...driver.com>, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] tun: signedness bug in tun_get_user()

On Thu, Aug 15, 2013 at 05:58:40PM +0300, Michael S. Tsirkin wrote:
> On Thu, Aug 15, 2013 at 05:04:49PM +0300, Michael S. Tsirkin wrote:
> > On Thu, Aug 15, 2013 at 03:52:57PM +0300, Dan Carpenter wrote:
> > > The recent fix d9bf5f1309 "tun: compare with 0 instead of total_len" is
> > > not totally correct.  Because "len" and "sizeof()" are size_t type, that
> > > means they are never less than zero.
> > > 
> > > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > 
> > Acked-by: Michael S. Tsirkin <mst@...hat.com>
> 
> Alternatively how about we revert the original patch?
> This is not the only issue it introduced and it doesn't
> actually fix any bugs.
> 
> > > 
> > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> > > index af987f0..7ed13cc 100644
> > > --- a/drivers/net/tun.c
> > > +++ b/drivers/net/tun.c
> > > @@ -977,8 +977,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> > >  	u32 rxhash;
> > >  
> > >  	if (!(tun->flags & TUN_NO_PI)) {
> > > -		if ((len -= sizeof(pi)) < 0)
> > > +		if (len < sizeof(pi))
> > >  			return -EINVAL;
> > > +		len -= sizeof(pi);
> > >  
> > >  		if (memcpy_fromiovecend((void *)&pi, iv, 0, sizeof(pi)))
> > >  			return -EFAULT;
> > > @@ -986,8 +987,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> > >  	}
> > >  
> > >  	if (tun->flags & TUN_VNET_HDR) {
> > > -		if ((len -= tun->vnet_hdr_sz) < 0)
> > > +		if (len < tun->vnet_hdr_sz)
> > >  			return -EINVAL;

And to be even more explicit, this still doesn't handle the
case vnet_hdr_sz < 0 properly.


> > > +		len -= tun->vnet_hdr_sz;
> > >  
> > >  		if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
> > >  			return -EFAULT;
--
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