net: Fix use after free by removing length arg from sk_data_ready callbacks.

Several spots in the kernel perform a sequence like:

	skb_queue_tail(&sk->s_receive_queue, skb);
	sk->sk_data_ready(sk, skb->len);

But at the moment we place the SKB onto the socket receive queue it
can be consumed and freed up.  So this skb->len access is potentially
to freed up memory.

Furthermore, the skb->len can be modified by the consumer so it is
possible that the value isn't accurate.

And finally, no actual implementation of this callback actually uses
the length argument.  And since nobody actually cared about it's
value, lots of call sites pass arbitrary values in such as '0' and
even '1'.

So just remove the length argument from the callback, that way there
is no confusion whatsoever and all of these use-after-free cases get
fixed as a side effect.

Based upon a patch by Eric Dumazet and his suggestion to audit this
issue tree-wide.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 3 deletions

diff --git a/net/decnet/dn_nsp_in.c b/net/decnet/dn_nsp_in.c
index c344163e6ac0..fe5f01485d33 100644
--- a/net/decnet/dn_nsp_in.c
+++ b/net/decnet/dn_nsp_in.c
@@ -585,7 +585,6 @@ out:
 static __inline__ int dn_queue_skb(struct sock *sk, struct sk_buff *skb, int sig, struct sk_buff_head *queue)
 {
         int err;
-        int skb_len;
 
         /* Cast skb->rcvbuf to unsigned... It's pointless, but reduces
            number of warnings when compiling with -W --ANK
@@ -600,12 +599,11 @@ static __inline__ int dn_queue_skb(struct sock *sk, struct sk_buff *skb, int sig
         if (err)
                 goto out;
 
-        skb_len = skb->len;
         skb_set_owner_r(skb, sk);
         skb_queue_tail(queue, skb);
 
         if (!sock_flag(sk, SOCK_DEAD))
-                sk->sk_data_ready(sk, skb_len);
+                sk->sk_data_ready(sk);
 out:
         return err;
 }