[PATCH 3.2 120/126] dccp: limit sk_filter trim to payload

[Ben Hutchings]

3.2.85-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Willem de Bruijn <willemb@xxxxxxxxxx>

commit 4f0c40d94461cfd23893a17335b2ab78ecb333c8 upstream.

Dccp verifies packet integrity, including length, at initial rcv in
dccp_invalid_packet, later pulls headers in dccp_enqueue_skb.

A call to sk_filter in-between can cause __skb_pull to wrap skb->len.
skb_copy_datagram_msg interprets this as a negative value, so
(correctly) fails with EFAULT. The negative length is reported in
ioctl SIOCINQ or possibly in a DCCP_WARN in dccp_close.

Introduce an sk_receive_skb variant that caps how small a filter
program can trim packets, and call this in dccp with the header
length. Excessively trimmed packets are now processed normally and
queued for reception as 0B payloads.

Fixes: 7c657876b63c ("[DCCP]: Initial implementation")
Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1268,8 +1268,13 @@ static inline void sock_put(struct sock
 		sk_free(sk);
 }
 
-extern int sk_receive_skb(struct sock *sk, struct sk_buff *skb,
-			  const int nested);
+int __sk_receive_skb(struct sock *sk, struct sk_buff *skb, const int nested,
+		     unsigned int trim_cap);
+static inline int sk_receive_skb(struct sock *sk, struct sk_buff *skb,
+				 const int nested)
+{
+	return __sk_receive_skb(sk, skb, nested, 1);
+}
 
 static inline void sk_tx_queue_set(struct sock *sk, int tx_queue)
 {
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -336,11 +336,12 @@ int sock_queue_rcv_skb(struct sock *sk,
 }
 EXPORT_SYMBOL(sock_queue_rcv_skb);
 
-int sk_receive_skb(struct sock *sk, struct sk_buff *skb, const int nested)
+int __sk_receive_skb(struct sock *sk, struct sk_buff *skb,
+		     const int nested, unsigned int trim_cap)
 {
 	int rc = NET_RX_SUCCESS;
 
-	if (sk_filter(sk, skb))
+	if (sk_filter_trim_cap(sk, skb, trim_cap))
 		goto discard_and_relse;
 
 	skb->dev = NULL;
@@ -376,7 +377,7 @@ discard_and_relse:
 	kfree_skb(skb);
 	goto out;
 }
-EXPORT_SYMBOL(sk_receive_skb);
+EXPORT_SYMBOL(__sk_receive_skb);
 
 void sk_reset_txq(struct sock *sk)
 {
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -877,7 +877,7 @@ static int dccp_v4_rcv(struct sk_buff *s
 		goto discard_and_relse;
 	nf_reset(skb);
 
-	return sk_receive_skb(sk, skb, 1);
+	return __sk_receive_skb(sk, skb, 1, dh->dccph_doff * 4);
 
 no_dccp_socket:
 	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -817,7 +817,7 @@ static int dccp_v6_rcv(struct sk_buff *s
 	if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb))
 		goto discard_and_relse;
 
-	return sk_receive_skb(sk, skb, 1) ? -1 : 0;
+	return __sk_receive_skb(sk, skb, 1, dh->dccph_doff * 4) ? -1 : 0;
 
 no_dccp_socket:
 	if (!xfrm6_policy_check(NULL, XFRM_POLICY_IN, skb))