mac80211: warn when receiving frames with unaligned data

This patch makes mac80211 warn (once) when the driver passes up a
frame in which the payload data is not aligned on a four-byte
boundary, with a long comment for people who run into the condition
and need to know what to do.

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

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 00f908d9275e3e69a92daf1cc4d6741015d051d5..a7263fc476bdd4a0936f983b3acf298a36faafa1 100644 (file)
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1443,6 +1443,7 @@ void __ieee80211_rx(struct ieee80211_hw *hw, struct sk_buff *skb,
        struct ieee80211_sub_if_data *prev = NULL;
        struct sk_buff *skb_new;
        u8 *bssid;
+       int hdrlen;
 
        /*
         * key references and virtual interfaces are protected using RCU
@@ -1472,6 +1473,18 @@ void __ieee80211_rx(struct ieee80211_hw *hw, struct sk_buff *skb,
        rx.fc = le16_to_cpu(hdr->frame_control);
        type = rx.fc & IEEE80211_FCTL_FTYPE;
 
+       /*
+        * Drivers are required to align the payload data to a four-byte
+        * boundary, so the last two bits of the address where it starts
+        * may not be set. The header is required to be directly before
+        * the payload data, padding like atheros hardware adds which is
+        * inbetween the 802.11 header and the payload is not supported,
+        * the driver is required to move the 802.11 header further back
+        * in that case.
+        */
+       hdrlen = ieee80211_get_hdrlen(rx.fc);
+       WARN_ON_ONCE(((unsigned long)(skb->data + hdrlen)) & 3);
+
        if (type == IEEE80211_FTYPE_DATA || type == IEEE80211_FTYPE_MGMT)
                local->dot11ReceivedFragmentCount++;