[PATCH 3.16 298/306] dccp: limit sk_filter trim to payload

Ben Hutchings
2017-02-15T23:13:55Z

From: Willem de Bruijn <willemb@google.com>

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@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
include/net/sock.h | 8 +++++++-
net/core/sock.c | 7 ++++---
net/dccp/ipv4.c | 2 +-
net/dccp/ipv6.c | 2 +-
4 files changed, 13 insertions(+), 6 deletions(-)

--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1669,7 +1669,13 @@ static inline void sock_put(struct sock
*/
void sock_gen_put(struct sock *sk);

-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
@@ -487,11 +487,12 @@ 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;
@@ -527,7 +528,7 @@ discard_and_relse:
kfree_skb(skb);
goto out;
}
-EXPORT_SYMBOL(sk_receive_skb);
+EXPORT_SYMBOL(__sk_receive_skb);

struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie)
{
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -890,7 +890,7 @@ 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
@@ -804,7 +804,7 @@ 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))