batman-adv: fix potential kernel paging errors for unicast transmissions

There are several functions which might reallocate skb data. Currently
some places keep reusing their old ethhdr pointer regardless of whether
they became invalid after such a reallocation or not. This potentially
leads to kernel paging errors.

This patch fixes these by refetching the ethdr pointer after the
potential reallocations.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>

1 files changed, 8 insertions, 1 deletions

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index 700d0b49742d..0f04e1c302b4 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -180,6 +180,9 @@ static int batadv_interface_tx(struct sk_buff *skb,
         if (batadv_bla_tx(bat_priv, skb, vid))
                 goto dropped;
 
+        /* skb->data might have been reallocated by batadv_bla_tx() */
+        ethhdr = (struct ethhdr *)skb->data;
+
         /* Register the client MAC in the transtable */
         if (!is_multicast_ether_addr(ethhdr->h_source))
                 batadv_tt_local_add(soft_iface, ethhdr->h_source, skb->skb_iif);
@@ -220,6 +223,10 @@ static int batadv_interface_tx(struct sk_buff *skb,
                 default:
                         break;
                 }
+
+                /* reminder: ethhdr might have become unusable from here on
+                 * (batadv_gw_is_dhcp_target() might have reallocated skb data)
+                 */
         }
 
         /* ethernet packet should be broadcasted */
@@ -266,7 +273,7 @@ static int batadv_interface_tx(struct sk_buff *skb,
         /* unicast packet */
         } else {
                 if (atomic_read(&bat_priv->gw_mode) != BATADV_GW_MODE_OFF) {
-                        ret = batadv_gw_out_of_range(bat_priv, skb, ethhdr);
+                        ret = batadv_gw_out_of_range(bat_priv, skb);
                         if (ret)
                                 goto dropped;
                 }