batman-adv: check for more space before accessing the skb

In batadv_check_unicast_ttvn() the code accesses both the unicast header and the
Ethernet header in the payload. For this reason pskb_may_pull() must be invoked
to check for the required space.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index 456a0a9f8831..46dd5b47ed29 100644
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -908,8 +908,12 @@ static int batadv_check_unicast_ttvn(struct batadv_priv *bat_priv,
         bool tt_poss_change;
         int is_old_ttvn;
 
-        /* I could need to modify it */
-        if (skb_cow(skb, sizeof(struct batadv_unicast_packet)) < 0)
+        /* check if there is enough data before accessing it */
+        if (pskb_may_pull(skb, sizeof(*unicast_packet) + ETH_HLEN) < 0)
+                return 0;
+
+        /* create a copy of the skb (in case of for re-routing) to modify it. */
+        if (skb_cow(skb, sizeof(*unicast_packet)) < 0)
                 return 0;
 
         unicast_packet = (struct batadv_unicast_packet *)skb->data;