mac80211: validate TIM IE length (redux)

The TIM IE must not be shorter than 4 bytes, so verify that
when parsing it and use the proper type. To ease that adjust
struct ieee80211_tim_ie to have a virtual bitmap of size
at least 1.

Also check that the TIM IE is actually present before trying
to parse it!

Because other people may need the function, make it a static
inline in ieee80211.h.

(The original "mac80211: validate TIM IE length" was a minimal fix for
2.6.30.  This purports to be the full, correct fix. -- JWL)

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 31 insertions, 1 deletions

diff --git a/include/linux/ieee80211.h b/include/linux/ieee80211.h
index 53563d53b5ad..c52e7fba4e40 100644
--- a/include/linux/ieee80211.h
+++ b/include/linux/ieee80211.h
@@ -540,7 +540,7 @@ struct ieee80211_tim_ie {
         u8 dtim_period;
         u8 bitmap_ctrl;
         /* variable size: 1 - 251 bytes */
-        u8 virtual_map[0];
+        u8 virtual_map[1];
 } __attribute__ ((packed));
 
 #define WLAN_SA_QUERY_TR_ID_LEN 16
@@ -1392,4 +1392,34 @@ static inline unsigned long ieee80211_tu_to_usec(unsigned long tu)
         return 1024 * tu;
 }
 
+/**
+ * ieee80211_check_tim - check if AID bit is set in TIM
+ * @tim: the TIM IE
+ * @tim_len: length of the TIM IE
+ * @aid: the AID to look for
+ */
+static inline bool ieee80211_check_tim(struct ieee80211_tim_ie *tim,
+                                       u8 tim_len, u16 aid)
+{
+        u8 mask;
+        u8 index, indexn1, indexn2;
+
+        if (unlikely(!tim || tim_len < sizeof(*tim)))
+                return false;
+
+        aid &= 0x3fff;
+        index = aid / 8;
+        mask  = 1 << (aid & 7);
+
+        indexn1 = tim->bitmap_ctrl & 0xfe;
+        indexn2 = tim_len + indexn1 - 4;
+
+        if (index < indexn1 || index > indexn2)
+                return false;
+
+        index -= indexn1;
+
+        return !!(tim->virtual_map[index] & mask);
+}
+
 #endif /* LINUX_IEEE80211_H */