Bluetooth: 6lowpan: Fix memory corruption of ipv6 destination address

The memcpy of ipv6 header destination address to the skb control block
(sbk->cb) in header_create() results in currupted memory when bt_xmit()
is issued. The skb->cb is "released" in the return of header_create()
making room for lower layer to minipulate the skb->cb.

The value retrieved in bt_xmit is not persistent across header creation
and sending, and the lower layer will overwrite portions of skb->cb,
making the copied destination address wrong.

The memory corruption will lead to non-working multicast as the first 4
bytes of the copied destination address is replaced by a value that
resolves into a non-multicast prefix.

This fix removes the dependency on the skb control block between header
creation and send, by moving the destination address memcpy to the send
function path (setup_create, which is called from bt_xmit).

Signed-off-by: Glenn Ruben Bakke <glenn.ruben.bakke@nordicsemi.no>
Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Cc: stable@vger.kernel.org # 4.5+

1 files changed, 4 insertions, 7 deletions

diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index 38e82ddd7ccd..780089d75915 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -434,15 +434,18 @@ static int setup_header(struct sk_buff *skb, struct net_device *netdev,
                         bdaddr_t *peer_addr, u8 *peer_addr_type)
 {
         struct in6_addr ipv6_daddr;
+        struct ipv6hdr *hdr;
         struct lowpan_btle_dev *dev;
         struct lowpan_peer *peer;
         bdaddr_t addr, *any = BDADDR_ANY;
         u8 *daddr = any->b;
         int err, status = 0;
 
+        hdr = ipv6_hdr(skb);
+
         dev = lowpan_btle_dev(netdev);
 
-        memcpy(&ipv6_daddr, &lowpan_cb(skb)->addr, sizeof(ipv6_daddr));
+        memcpy(&ipv6_daddr, &hdr->daddr, sizeof(ipv6_daddr));
 
         if (ipv6_addr_is_multicast(&ipv6_daddr)) {
                 lowpan_cb(skb)->chan = NULL;
@@ -492,15 +495,9 @@ static int header_create(struct sk_buff *skb, struct net_device *netdev,
                          unsigned short type, const void *_daddr,
                          const void *_saddr, unsigned int len)
 {
-        struct ipv6hdr *hdr;
-
         if (type != ETH_P_IPV6)
                 return -EINVAL;
 
-        hdr = ipv6_hdr(skb);
-
-        memcpy(&lowpan_cb(skb)->addr, &hdr->daddr, sizeof(struct in6_addr));
-
         return 0;
 }