linux-kernel - Re: [PATCH] net: qrtr: fix memory leak in qrtr_tun_read

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Date:   Thu, 26 Sep 2019 22:16:32 -0500
From:   Navid Emamdoost <navid.emamdoost@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     emamd001@....edu, smccaman@....edu, kjlu@....edu,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: qrtr: fix memory leak in qrtr_tun_read_iter

On Thu, Sep 26, 2019 at 12:21:12AM +0100, Al Viro wrote:
> On Wed, Sep 25, 2019 at 06:04:13PM -0500, Navid Emamdoost wrote:
> > In qrtr_tun_read_iter we need an error handling path to appropriately
> > release skb in cases of error.
> 
> Release _what_ skb?
It is not a leak clearly! My bad ...
> 
> > Signed-off-by: Navid Emamdoost <navid.emamdoost@...il.com>
> > ---
> >  net/qrtr/tun.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> > 
> > diff --git a/net/qrtr/tun.c b/net/qrtr/tun.c
> > index e35869e81766..0f6e6d1d2901 100644
> > --- a/net/qrtr/tun.c
> > +++ b/net/qrtr/tun.c
> > @@ -54,19 +54,24 @@ static ssize_t qrtr_tun_read_iter(struct kiocb *iocb, struct iov_iter *to)
> >  	int count;
> >  
> >  	while (!(skb = skb_dequeue(&tun->queue))) {
> 
> The body of the loop is entered only if the loop condition has
> evaluated true.  In this case, it means that the value of
> 	!(skb = skb_dequeue(&tun->queue))
> had been true, i.e. the value of
> 	skb = skb_dequeue(&tun->queue)
> has been NULL, i.e. that skb_dequeue() has returned NULL, which had
> been copied into skb.
> 
> In other words, in the body of that loop we have skb equal to NULL.
> 
> > -		if (filp->f_flags & O_NONBLOCK)
> > -			return -EAGAIN;
> > +		if (filp->f_flags & O_NONBLOCK) {
> > +			count = -EAGAIN;
> > +			goto out;
> > +		}
> >  
> >  		/* Wait until we get data or the endpoint goes away */
> >  		if (wait_event_interruptible(tun->readq,
> > -					     !skb_queue_empty(&tun->queue)))
> > -			return -ERESTARTSYS;
> > +					     !skb_queue_empty(&tun->queue))) {
> > +			count = -ERESTARTSYS;
> > +			goto out;
> > +		}
> >  	}
> 
> The meaning of that loop is fairly clear, isn't it?  Keep looking int
> tun->queue until an skb shows up there.  If it's not immediately there,
> fail with -EAGAIN for non-blocking files and wait on tun->readq until
> some skb arrives.

Thanks for the explainations.

Navid.