[IEEE80211]: avoid integer underflow for runt rx frames

Reported by Chris Evans <scarybeasts@gmail.com>:

> The summary is that an evil 80211 frame can crash out a victim's
> machine. It only applies to drivers using the 80211 wireless code, and
> only then to certain drivers (and even then depends on a card's
> firmware not dropping a dubious packet). I must confess I'm not
> keeping track of Linux wireless support, and the different protocol
> stacks etc.
>
> Details are as follows:
>
> ieee80211_rx() does not explicitly check that "skb->len >= hdrlen".
> There are other skb->len checks, but not enough to prevent a subtle
> off-by-two error if the frame has the IEEE80211_STYPE_QOS_DATA flag
> set.
>
> This leads to integer underflow and crash here:
>
> if (frag != 0)
>    flen -= hdrlen;
>
> (flen is subsequently used as a memcpy length parameter).

How about this?

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 0 deletions

diff --git a/net/ieee80211/ieee80211_rx.c b/net/ieee80211/ieee80211_rx.c
index f2de2e48b021..6284c99b456e 100644
--- a/net/ieee80211/ieee80211_rx.c
+++ b/net/ieee80211/ieee80211_rx.c
@@ -366,6 +366,12 @@ int ieee80211_rx(struct ieee80211_device *ieee, struct sk_buff *skb,
         frag = WLAN_GET_SEQ_FRAG(sc);
         hdrlen = ieee80211_get_hdrlen(fc);
 
+        if (skb->len < hdrlen) {
+                printk(KERN_INFO "%s: invalid SKB length %d\n",
+                        dev->name, skb->len);
+                goto rx_dropped;
+        }
+
         /* Put this code here so that we avoid duplicating it in all
          * Rx paths. - Jean II */
 #ifdef CONFIG_WIRELESS_EXT