net-timestamp: only report sw timestamp if reporting bit is set

The timestamping API has separate bits for generating and reporting
timestamps. A software timestamp should only be reported for a packet
when the packet has the relevant generation flag (SKBTX_..) set
and the socket has reporting bit SOF_TIMESTAMPING_SOFTWARE set.

The second check was accidentally removed. Reinstitute the original
behavior.

Tested:
  Without this patch, Documentation/networking/txtimestamp reports
  timestamps regardless of whether SOF_TIMESTAMPING_SOFTWARE is set.
  After the patch, it only reports them when the flag is set.

Fixes: f24b9be ("net-timestamp: extend SCM_TIMESTAMPING ancillary data struct")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -2165,9 +2165,7 @@ sock_recv_timestamp(struct msghdr *msg, struct sock *sk, struct sk_buff *skb)
 	 */
 	if (sock_flag(sk, SOCK_RCVTSTAMP) ||
 	    (sk->sk_tsflags & SOF_TIMESTAMPING_RX_SOFTWARE) ||
-	    (kt.tv64 &&
-	     (sk->sk_tsflags & SOF_TIMESTAMPING_SOFTWARE ||
-	      skb_shinfo(skb)->tx_flags & SKBTX_ANY_SW_TSTAMP)) ||
+	    (kt.tv64 && sk->sk_tsflags & SOF_TIMESTAMPING_SOFTWARE) ||
 	    (hwtstamps->hwtstamp.tv64 &&
 	     (sk->sk_tsflags & SOF_TIMESTAMPING_RAW_HARDWARE)))
 		__sock_recv_timestamp(msg, sk, skb);

net/socket.c

@@ -734,8 +734,7 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
 	}
 
 	memset(&tss, 0, sizeof(tss));
-	if ((sk->sk_tsflags & SOF_TIMESTAMPING_SOFTWARE ||
-	     skb_shinfo(skb)->tx_flags & SKBTX_ANY_SW_TSTAMP) &&
+	if ((sk->sk_tsflags & SOF_TIMESTAMPING_SOFTWARE) &&
 	    ktime_to_timespec_cond(skb->tstamp, tss.ts + 0))
 		empty = 0;
 	if (shhwtstamps &&