[PATCH] mac80211: warn when receiving frames with unaligned data

Johannes Berg
2007-12-18T14:11:35Z

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-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
---
net/mac80211/rx.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

--- everything.orig/net/mac80211/rx.c 2007-12-18 14:47:18.433014323 +0100
+++ everything/net/mac80211/rx.c 2007-12-18 14:48:47.113014051 +0100
@@ -1619,6 +1619,7 @@ void __ieee80211_rx(struct ieee80211_hw
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
@@ -1648,6 +1649,18 @@ void __ieee80211_rx(struct ieee80211_hw
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++;