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

[Alexey Khoroshilov]

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().

> > @@ -956,8 +955,12 @@ static int rtl8187_start(struct ieee80211_hw *dev)
> >                    (RETRY_COUNT < 8  /* short retry limit */) |
> >                    (RETRY_COUNT < 0  /* long retry limit */) |
> >                    (7 < 21 /* MAX TX DMA */));
> > -        rtl8187_init_urbs(dev);
> > -        rtl8187b_init_status_urb(dev);
> > +        ret = rtl8187_init_urbs(dev);
> > +        if (ret)
> > +            goto rtl8187_start_exit;
> > +        ret = rtl8187b_init_status_urb(dev);
> > +        if (ret)
> > +            usb_kill_anchored_urbs(&priv->anchored);
> >          goto rtl8187_start_exit;
> >      }
> >
> > @@ -966,7 +969,9 @@ static int rtl8187_start(struct ieee80211_hw *dev)
> >      rtl818x_iowrite32(priv, &priv->map->MAR[0], ~0);
> >      rtl818x_iowrite32(priv, &priv->map->MAR[1], ~0);
> >
> > -    rtl8187_init_urbs(dev);
> > +    ret = rtl8187_init_urbs(dev);
> > +    if (ret)
> > +        goto rtl8187_start_exit;
> >
> >      reg = RTL818X_RX_CONF_ONLYERLPKT |
> >            RTL818X_RX_CONF_RX_AUTORESETPHY |
> > --
> > 1.8.1.2

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