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, 5 insertions, 7 deletions

diff --git a/net/phonet/pep-gprs.c b/net/phonet/pep-gprs.c
index a2fba7e..66dc65e 100644
--- a/net/phonet/pep-gprs.c
+++ b/net/phonet/pep-gprs.c
@@ -37,7 +37,7 @@
 struct gprs_dev {
 	struct sock		*sk;
 	void			(*old_state_change)(struct sock *);
-	void			(*old_data_ready)(struct sock *, int);
+	void			(*old_data_ready)(struct sock *);
 	void			(*old_write_space)(struct sock *);
 
 	struct net_device	*dev;
@@ -146,7 +146,7 @@ drop:
 	return err;
 }
 
-static void gprs_data_ready(struct sock *sk, int len)
+static void gprs_data_ready(struct sock *sk)
 {
 	struct gprs_dev *gp = sk->sk_user_data;
 	struct sk_buff *skb;
diff --git a/net/phonet/pep.c b/net/phonet/pep.c
index e774117..70a547e 100644
--- a/net/phonet/pep.c
+++ b/net/phonet/pep.c
@@ -462,10 +462,9 @@ out:
 queue:
 	skb->dev = NULL;
 	skb_set_owner_r(skb, sk);
-	err = skb->len;
 	skb_queue_tail(queue, skb);
 	if (!sock_flag(sk, SOCK_DEAD))
-		sk->sk_data_ready(sk, err);
+		sk->sk_data_ready(sk);
 	return NET_RX_SUCCESS;
 }
 
@@ -587,10 +586,9 @@ static int pipe_handler_do_rcv(struct sock *sk, struct sk_buff *skb)
 		pn->rx_credits--;
 		skb->dev = NULL;
 		skb_set_owner_r(skb, sk);
-		err = skb->len;
 		skb_queue_tail(&sk->sk_receive_queue, skb);
 		if (!sock_flag(sk, SOCK_DEAD))
-			sk->sk_data_ready(sk, err);
+			sk->sk_data_ready(sk);
 		return NET_RX_SUCCESS;
 
 	case PNS_PEP_CONNECT_RESP:
@@ -698,7 +696,7 @@ static int pep_do_rcv(struct sock *sk, struct sk_buff *skb)
 		skb_queue_head(&sk->sk_receive_queue, skb);
 		sk_acceptq_added(sk);
 		if (!sock_flag(sk, SOCK_DEAD))
-			sk->sk_data_ready(sk, 0);
+			sk->sk_data_ready(sk);
 		return NET_RX_SUCCESS;
 
 	case PNS_PEP_DISCONNECT_REQ: