can-raw: Fix skb_orphan_try handling

Commit fc6055a5ba31e2c14e36e8939f9bf2b6d586a7f5 (net: Introduce
skb_orphan_try()) allows an early orphan of the skb and takes care on
tx timestamping, which needs the sk-reference in the skb on driver level.
So does the can-raw socket, which has not been taken into account here.

The patch below adds a 'prevent_sk_orphan' bit in the skb tx shared info,
which fixes the problem discovered by Matthias Fuchs here:

      http://marc.info/?t=128030411900003&r=1&w=2

Even if it's not a primary tx timestamp topic it fits well into some skb
shared tx context. Or should be find a different place for the information to
protect the sk reference until it reaches the driver level?

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 7 insertions, 1 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index d89876b806a0..d20d9e7a9bbd 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -169,6 +169,7 @@ struct skb_shared_hwtstamps {
  * @software:           generate software time stamp
  * @in_progress:        device driver is going to provide
  *                      hardware time stamp
+ * @prevent_sk_orphan:  make sk reference available on driver level
  * @flags:              all shared_tx flags
  *
  * These flags are attached to packets as part of the
@@ -178,7 +179,8 @@ union skb_shared_tx {
         struct {
                 __u8    hardware:1,
                         software:1,
-                        in_progress:1;
+                        in_progress:1,
+                        prevent_sk_orphan:1;
         };
         __u8 flags;
 };
diff --git a/net/can/raw.c b/net/can/raw.c
index ccfe633eec8e..a10e3338f084 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -650,6 +650,10 @@ static int raw_sendmsg(struct kiocb *iocb, struct socket *sock,
         err = sock_tx_timestamp(msg, sk, skb_tx(skb));
         if (err < 0)
                 goto free_skb;
+
+        /* to be able to check the received tx sock reference in raw_rcv() */
+        skb_tx(skb)->prevent_sk_orphan = 1;
+
         skb->dev = dev;
         skb->sk  = sk;