[MAC80211]: Improve sanity checks on injected packets

Michael Wu noticed that the skb length checking is not taken care of enough when
a packet is presented on the Monitor interface for injection.

This patch improves the sanity checking and removes fake offsets placed
into the skb network and transport header.

Signed-off-by: Andy Green <andy@warmcat.com>
Signed-off-by: Jiri Benc <jbenc@suse.cz>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 36761c7139bc9bcc0ed9fd12a90c05dbf6be417b..457166889cc75ef31c645a72ab23c632e111501a 100644 (file)
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1270,46 +1270,54 @@ int ieee80211_monitor_start_xmit(struct sk_buff *skb,
        struct ieee80211_tx_packet_data *pkt_data;
        struct ieee80211_radiotap_header *prthdr =
                (struct ieee80211_radiotap_header *)skb->data;
-       u16 len;
+       u16 len_rthdr;
 
-       /*
-        * there must be a radiotap header at the
-        * start in this case
-        */
-       if (unlikely(prthdr->it_version)) {
-               /* only version 0 is supported */
-               dev_kfree_skb(skb);
-               return NETDEV_TX_OK;
-       }
+       /* check for not even having the fixed radiotap header part */
+       if (unlikely(skb->len < sizeof(struct ieee80211_radiotap_header)))
+               goto fail; /* too short to be possibly valid */
+
+       /* is it a header version we can trust to find length from? */
+       if (unlikely(prthdr->it_version))
+               goto fail; /* only version 0 is supported */
+
+       /* then there must be a radiotap header with a length we can use */
+       len_rthdr = ieee80211_get_radiotap_len(skb->data);
+
+       /* does the skb contain enough to deliver on the alleged length? */
+       if (unlikely(skb->len < len_rthdr))
+               goto fail; /* skb too short for claimed rt header extent */
 
        skb->dev = local->mdev;
 
        pkt_data = (struct ieee80211_tx_packet_data *)skb->cb;
        memset(pkt_data, 0, sizeof(*pkt_data));
+       /* needed because we set skb device to master */
        pkt_data->ifindex = dev->ifindex;
+
        pkt_data->mgmt_iface = 0;
        pkt_data->do_not_encrypt = 1;
 
-       /* above needed because we set skb device to master */
-
        /*
         * fix up the pointers accounting for the radiotap
         * header still being in there.  We are being given
         * a precooked IEEE80211 header so no need for
         * normal processing
         */
-       len = le16_to_cpu(get_unaligned(&prthdr->it_len));
-       skb_set_mac_header(skb, len);
-       skb_set_network_header(skb, len + sizeof(struct ieee80211_hdr));
-       skb_set_transport_header(skb, len + sizeof(struct ieee80211_hdr));
-
+       skb_set_mac_header(skb, len_rthdr);
        /*
-        * pass the radiotap header up to
-        * the next stage intact
+        * these are just fixed to the end of the rt area since we
+        * don't have any better information and at this point, nobody cares
         */
-       dev_queue_xmit(skb);
+       skb_set_network_header(skb, len_rthdr);
+       skb_set_transport_header(skb, len_rthdr);
 
+       /* pass the radiotap header up to the next stage intact */
+       dev_queue_xmit(skb);
        return NETDEV_TX_OK;
+
+fail:
+       dev_kfree_skb(skb);
+       return NETDEV_TX_OK; /* meaning, we dealt with the skb */
 }
 
 /**