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>

2 files changed, 3 insertions, 3 deletions

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 270d5bd97d8..e13519e9df8 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -6745,7 +6745,7 @@ do_nonblock:
 	goto out;
 }
 
-void sctp_data_ready(struct sock *sk, int len)
+void sctp_data_ready(struct sock *sk)
 {
 	struct socket_wq *wq;
 
diff --git a/net/sctp/ulpqueue.c b/net/sctp/ulpqueue.c
index 5dc94117e9d..7144eb6a1b9 100644
--- a/net/sctp/ulpqueue.c
+++ b/net/sctp/ulpqueue.c
@@ -259,7 +259,7 @@ int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
 		sctp_ulpq_clear_pd(ulpq);
 
 	if (queue == &sk->sk_receive_queue)
-		sk->sk_data_ready(sk, 0);
+		sk->sk_data_ready(sk);
 	return 1;
 
 out_free:
@@ -1135,5 +1135,5 @@ void sctp_ulpq_abort_pd(struct sctp_ulpq *ulpq, gfp_t gfp)
 
 	/* If there is data waiting, send it up the socket now. */
 	if (sctp_ulpq_clear_pd(ulpq) || ev)
-		sk->sk_data_ready(sk, 0);
+		sk->sk_data_ready(sk);
 }