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

batadv_send_skb_prepare_unicast(_4addr) might reallocate the
skb's data. If it does then our ethhdr pointer is not valid
anymore in batadv_send_skb_unicast(), resulting in a kernel
paging error.

Fixing this by refetching the ethhdr pointer after the
potential reallocation.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/net/batman-adv/send.c b/net/batman-adv/send.c
index 579f5f00a385..843febd1e519 100644
--- a/net/batman-adv/send.c
+++ b/net/batman-adv/send.c
@@ -254,9 +254,9 @@ static int batadv_send_skb_unicast(struct batadv_priv *bat_priv,
                                    struct batadv_orig_node *orig_node,
                                    unsigned short vid)
 {
-        struct ethhdr *ethhdr = (struct ethhdr *)skb->data;
+        struct ethhdr *ethhdr;
         struct batadv_unicast_packet *unicast_packet;
-        int ret = NET_XMIT_DROP;
+        int ret = NET_XMIT_DROP, hdr_size;
 
         if (!orig_node)
                 goto out;
@@ -265,12 +265,16 @@ static int batadv_send_skb_unicast(struct batadv_priv *bat_priv,
         case BATADV_UNICAST:
                 if (!batadv_send_skb_prepare_unicast(skb, orig_node))
                         goto out;
+
+                hdr_size = sizeof(*unicast_packet);
                 break;
         case BATADV_UNICAST_4ADDR:
                 if (!batadv_send_skb_prepare_unicast_4addr(bat_priv, skb,
                                                            orig_node,
                                                            packet_subtype))
                         goto out;
+
+                hdr_size = sizeof(struct batadv_unicast_4addr_packet);
                 break;
         default:
                 /* this function supports UNICAST and UNICAST_4ADDR only. It
@@ -279,6 +283,7 @@ static int batadv_send_skb_unicast(struct batadv_priv *bat_priv,
                 goto out;
         }
 
+        ethhdr = (struct ethhdr *)(skb->data + hdr_size);
         unicast_packet = (struct batadv_unicast_packet *)skb->data;
 
         /* inform the destination node that we are still missing a correct route