mac80211: avoid kernel panic when building AMSDU from non-linear SKB

When building building AMSDU from non-linear SKB, we hit a
kernel panic when trying to push the padding to the tail.
Instead, put the padding at the head of the next subframe.
This also fixes the A-MSDU subframes to not have the padding
accounted in the length field and not have pad at all for
the last subframe, both required by the spec.

Fixes: 6e0456b54545 ("mac80211: add A-MSDU tx support")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Reviewed-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index fa1f1e63a2640fd405e42e5aeae9718b4ef12d2a..667a73d6eb5cf2689b5874f47facc79deba99f86 100644 (file)
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3073,27 +3073,18 @@ void ieee80211_clear_fast_xmit(struct sta_info *sta)
 }
 
 static bool ieee80211_amsdu_realloc_pad(struct ieee80211_local *local,
-                                       struct sk_buff *skb, int headroom,
-                                       int *subframe_len)
+                                       struct sk_buff *skb, int headroom)
 {
-       int amsdu_len = *subframe_len + sizeof(struct ethhdr);
-       int padding = (4 - amsdu_len) & 3;
-
-       if (skb_headroom(skb) < headroom || skb_tailroom(skb) < padding) {
+       if (skb_headroom(skb) < headroom) {
                I802_DEBUG_INC(local->tx_expand_skb_head);
 
-               if (pskb_expand_head(skb, headroom, padding, GFP_ATOMIC)) {
+               if (pskb_expand_head(skb, headroom, 0, GFP_ATOMIC)) {
                        wiphy_debug(local->hw.wiphy,
                                    "failed to reallocate TX buffer\n");
                        return false;
                }
        }
 
-       if (padding) {
-               *subframe_len += padding;
-               skb_put_zero(skb, padding);
-       }
-
        return true;
 }
 
@@ -3117,8 +3108,7 @@ static bool ieee80211_amsdu_prepare_head(struct ieee80211_sub_if_data *sdata,
        if (info->control.flags & IEEE80211_TX_CTRL_AMSDU)
                return true;
 
-       if (!ieee80211_amsdu_realloc_pad(local, skb, sizeof(*amsdu_hdr),
-                                        &subframe_len))
+       if (!ieee80211_amsdu_realloc_pad(local, skb, sizeof(*amsdu_hdr)))
                return false;
 
        data = skb_push(skb, sizeof(*amsdu_hdr));
@@ -3184,7 +3174,8 @@ static bool ieee80211_amsdu_aggregate(struct ieee80211_sub_if_data *sdata,
        void *data;
        bool ret = false;
        unsigned int orig_len;
-       int n = 1, nfrags;
+       int n = 1, nfrags, pad = 0;
+       u16 hdrlen;
 
        if (!ieee80211_hw_check(&local->hw, TX_AMSDU))
                return false;
@@ -3235,8 +3226,19 @@ static bool ieee80211_amsdu_aggregate(struct ieee80211_sub_if_data *sdata,
        if (max_frags && nfrags > max_frags)
                goto out;
 
-       if (!ieee80211_amsdu_realloc_pad(local, skb, sizeof(rfc1042_header) + 2,
-                                        &subframe_len))
+       /*
+        * Pad out the previous subframe to a multiple of 4 by adding the
+        * padding to the next one, that's being added. Note that head->len
+        * is the length of the full A-MSDU, but that works since each time
+        * we add a new subframe we pad out the previous one to a multiple
+        * of 4 and thus it no longer matters in the next round.
+        */
+       hdrlen = fast_tx->hdr_len - sizeof(rfc1042_header);
+       if ((head->len - hdrlen) & 3)
+               pad = 4 - ((head->len - hdrlen) & 3);
+
+       if (!ieee80211_amsdu_realloc_pad(local, skb, sizeof(rfc1042_header) +
+                                                    2 + pad))
                goto out;
 
        ret = true;
@@ -3248,6 +3250,8 @@ static bool ieee80211_amsdu_aggregate(struct ieee80211_sub_if_data *sdata,
        memcpy(data, &len, 2);
        memcpy(data + 2, rfc1042_header, sizeof(rfc1042_header));
 
+       memset(skb_push(skb, pad), 0, pad);
+
        head->len += skb->len;
        head->data_len += skb->len;
        *frag_tail = skb;