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/caif/caif_socket.c b/net/caif/caif_socket.c
index d6be3edb7a43..e8437094d15f 100644
--- a/net/caif/caif_socket.c
+++ b/net/caif/caif_socket.c
@@ -124,7 +124,6 @@ static void caif_flow_ctrl(struct sock *sk, int mode)
 static int caif_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 {
 	int err;
-	int skb_len;
 	unsigned long flags;
 	struct sk_buff_head *list = &sk->sk_receive_queue;
 	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);
@@ -153,14 +152,13 @@ static int caif_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	 * may be freed by other threads of control pulling packets
 	 * from the queue.
 	 */
-	skb_len = skb->len;
 	spin_lock_irqsave(&list->lock, flags);
 	if (!sock_flag(sk, SOCK_DEAD))
 		__skb_queue_tail(list, skb);
 	spin_unlock_irqrestore(&list->lock, flags);
 
 	if (!sock_flag(sk, SOCK_DEAD))
-		sk->sk_data_ready(sk, skb_len);
+		sk->sk_data_ready(sk);
 	else
 		kfree_skb(skb);
 	return 0;