Re: [PATCH] rtl8187: fix use after free on failure path in rtl8187_init_urbs()

[Alexey Khoroshilov]

On 02.09.2013 10:34, Hin-Tak Leung wrote:
> ------------------------------
> On Mon, Sep 2, 2013 05:06 BST Alexey Khoroshilov wrote:
>
> > On 01.09.2013 10:51, Hin-Tak Leung wrote:
> > > ------------------------------
> > > On Sat, Aug 31, 2013 22:18 BST Alexey Khoroshilov wrote:
> > >
> > > In case of __dev_alloc_skb() failure rtl8187_init_urbs()
> > > calls usb_free_urb(entry) where 'entry' can points to urb
> > > allocated at the previous iteration. That means refcnt will be
> > > decremented incorrectly and the urb can be used after memory
> > > deallocation.
> > >
> > > The patch fixes the issue and implements error handling of init_urbs
> > > in rtl8187_start().
> > >
> > > Found by Linux Driver Verification project (linuxtesting.org).
> > >
> > > Signed-off-by: Alexey Khoroshilov <khoroshilov@xxxxxxxxx>
> > > ---
> > > drivers/net/wireless/rtl818x/rtl8187/dev.c | 15 ++++++++++-----
> > > 1 file changed, 10 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/net/wireless/rtl818x/rtl8187/dev.c b/drivers/net/wireless/rtl818x/rtl8187/dev.c
> > > index f49220e..e83d53c 100644
> > > --- a/drivers/net/wireless/rtl818x/rtl8187/dev.c
> > > +++ b/drivers/net/wireless/rtl818x/rtl8187/dev.c
> > > @@ -438,17 +438,16 @@ static int rtl8187_init_urbs(struct ieee80211_hw *dev)
> > >            skb_queue_tail(&priv->rx_queue, skb);
> > >            usb_anchor_urb(entry, &priv->anchored);
> > >            ret = usb_submit_urb(entry, GFP_KERNEL);
> > > +        usb_free_urb(entry);
> > >            if (ret) {
> > >                skb_unlink(skb, &priv->rx_queue);
> > >                usb_unanchor_urb(entry);
> > >                goto err;
> > >            }
> > > -        usb_free_urb(entry);
> > >        }
> > >        return ret;
> > >
> > > err:
> > > -    usb_free_urb(entry);
> > >        kfree_skb(skb);
> > >        usb_kill_anchored_urbs(&priv->anchored);
> > >        return ret;
> > > This part looks wrong - you free_urb(entry) then unanchor_urb(entry).
> > I do not see any problems here.
> > usb_free_urb() just decrements refcnt of the urb.
> > While usb_anchor_urb() and usb_unanchor_urb() increment and decrement it
> > as well.
> > So actual memory deallocation will happen in usb_unanchor_urb().
> If the routines work as you say, they probably are misnamed, and/or prototyped wrongly?
> Also, you are making assumptions about how they are implemented, and relying
> on the implementation details to be fixed for eternity.
>
> I am just saying,
>
> XXX_free(some_entity);
> if(condtion)
>       do_stuff(some_entity);
>
> looks wrong, and if that's intentional, those routines really shouldn't be named as such.
There is an alias for usb_free_urb() named usb_put_urb().
I will resend the patch with such substitution.

--
Alexey
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