2 files changed, 79 insertions, 35 deletions

diff --git a/Documentation/DocBook/mac80211.tmpl b/Documentation/DocBook/mac80211.tmpl
index 77c3c202991b..bdf908a6e545 100644
--- a/Documentation/DocBook/mac80211.tmpl
+++ b/Documentation/DocBook/mac80211.tmpl
@@ -165,8 +165,8 @@ usage should require reading the full document.
 !Pinclude/net/mac80211.h Frame format
       </sect1>
       <sect1>
-        <title>Alignment issues</title>
-        <para>TBD</para>
+        <title>Packet alignment</title>
+!Pnet/mac80211/rx.c Packet alignment
       </sect1>
       <sect1>
         <title>Calling into mac80211 from interrupts</title>
diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index ddb966f58882..b68e082e99ce 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -102,7 +102,7 @@ ieee80211_rx_radiotap_len(struct ieee80211_local *local,
         return len;
 }
 
-/**
+/*
  * ieee80211_add_rx_radiotap_header - add radiotap header
  *
  * add a radiotap header containing all the fields which the hardware provided.
@@ -371,39 +371,50 @@ static void ieee80211_parse_qos(struct ieee80211_rx_data *rx)
         rx->skb->priority = (tid > 7) ? 0 : tid;
 }
 
-static void ieee80211_verify_ip_alignment(struct ieee80211_rx_data *rx)
+/**
+ * DOC: Packet alignment
+ *
+ * Drivers always need to pass packets that are aligned to two-byte boundaries
+ * to the stack.
+ *
+ * Additionally, should, if possible, align the payload data in a way that
+ * guarantees that the contained IP header is aligned to a four-byte
+ * boundary. In the case of regular frames, this simply means aligning the
+ * payload to a four-byte boundary (because either the IP header is directly
+ * contained, or IV/RFC1042 headers that have a length divisible by four are
+ * in front of it).
+ *
+ * With A-MSDU frames, however, the payload data address must yield two modulo
+ * four because there are 14-byte 802.3 headers within the A-MSDU frames that
+ * push the IP header further back to a multiple of four again. Thankfully, the
+ * specs were sane enough this time around to require padding each A-MSDU
+ * subframe to a length that is a multiple of four.
+ *
+ * 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 to be directly in front of the payload in that case.
+ */
+static void ieee80211_verify_alignment(struct ieee80211_rx_data *rx)
 {
-#ifdef CONFIG_MAC80211_DEBUG_PACKET_ALIGNMENT
         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
         int hdrlen;
 
+#ifndef CONFIG_MAC80211_DEBUG_PACKET_ALIGNMENT
+        return;
+#endif
+
+        if (WARN_ONCE((unsigned long)rx->skb->data & 1,
+                      "unaligned packet at 0x%p\n", rx->skb->data))
+                return;
+
         if (!ieee80211_is_data_present(hdr->frame_control))
                 return;
 
-        /*
-         * Drivers are required to align the payload data in a way that
-         * guarantees that the contained IP header is aligned to a four-
-         * byte boundary. In the case of regular frames, this simply means
-         * aligning the payload to a four-byte boundary (because either
-         * the IP header is directly contained, or IV/RFC1042 headers that
-         * have a length divisible by four are in front of it.
-         *
-         * With A-MSDU frames, however, the payload data address must
-         * yield two modulo four because there are 14-byte 802.3 headers
-         * within the A-MSDU frames that push the IP header further back
-         * to a multiple of four again. Thankfully, the specs were sane
-         * enough this time around to require padding each A-MSDU subframe
-         * to a length that is a multiple of four.
-         *
-         * 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_hdrlen(hdr->frame_control);
         if (rx->flags & IEEE80211_RX_AMSDU)
                 hdrlen += ETH_HLEN;
-        WARN_ON_ONCE(((unsigned long)(rx->skb->data + hdrlen)) & 3);
-#endif
+        WARN_ONCE(((unsigned long)(rx->skb->data + hdrlen)) & 3,
+                  "unaligned IP payload at 0x%p\n", rx->skb->data + hdrlen);
 }
 
 
@@ -1267,10 +1278,37 @@ ieee80211_deliver_skb(struct ieee80211_rx_data *rx)
         }
 
         if (skb) {
-                /* deliver to local stack */
-                skb->protocol = eth_type_trans(skb, dev);
-                memset(skb->cb, 0, sizeof(skb->cb));
-                netif_rx(skb);
+                int align __maybe_unused;
+
+#if defined(CONFIG_MAC80211_DEBUG_PACKET_ALIGNMENT) || !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
+                /*
+                 * 'align' will only take the values 0 or 2 here
+                 * since all frames are required to be aligned
+                 * to 2-byte boundaries when being passed to
+                 * mac80211. That also explains the __skb_push()
+                 * below.
+                 */
+                align = (unsigned long)skb->data & 4;
+                if (align) {
+                        if (WARN_ON(skb_headroom(skb) < 3)) {
+                                dev_kfree_skb(skb);
+                                skb = NULL;
+                        } else {
+                                u8 *data = skb->data;
+                                size_t len = skb->len;
+                                u8 *new = __skb_push(skb, align);
+                                memmove(new, data, len);
+                                __skb_trim(skb, len);
+                        }
+                }
+#endif
+
+                if (skb) {
+                        /* deliver to local stack */
+                        skb->protocol = eth_type_trans(skb, dev);
+                        memset(skb->cb, 0, sizeof(skb->cb));
+                        netif_rx(skb);
+                }
         }
 
         if (xmit_skb) {
@@ -1339,14 +1377,20 @@ ieee80211_rx_h_amsdu(struct ieee80211_rx_data *rx)
                 if (remaining <= subframe_len + padding)
                         frame = skb;
                 else {
-                        frame = dev_alloc_skb(local->hw.extra_tx_headroom +
-                                              subframe_len);
+                        /*
+                         * Allocate and reserve two bytes more for payload
+                         * alignment since sizeof(struct ethhdr) is 14.
+                         */
+                        frame = dev_alloc_skb(
+                                ALIGN(local->hw.extra_tx_headroom, 4) +
+                                subframe_len + 2);
 
                         if (frame == NULL)
                                 return RX_DROP_UNUSABLE;
 
-                        skb_reserve(frame, local->hw.extra_tx_headroom +
-                                    sizeof(struct ethhdr));
+                        skb_reserve(frame,
+                                    ALIGN(local->hw.extra_tx_headroom, 4) +
+                                    sizeof(struct ethhdr) + 2);
                         memcpy(skb_put(frame, ntohs(len)), skb->data,
                                 ntohs(len));
 
@@ -1976,7 +2020,7 @@ static void __ieee80211_rx_handle_packet(struct ieee80211_hw *hw,
                 rx.flags |= IEEE80211_RX_IN_SCAN;
 
         ieee80211_parse_qos(&rx);
-        ieee80211_verify_ip_alignment(&rx);
+        ieee80211_verify_alignment(&rx);
 
         skb = rx.skb;