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

[Hin-Tak Leung <htl10@users.sourceforge.net>]

------------------------------
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@ispras.ru>
>---
> 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).

>@@ -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
>