sctp: update the netstamp_needed counter when copying sockets

[ Upstream commit 01ce63c9 ]

Dmitry Vyukov reported that SCTP was triggering a WARN on socket destroy
related to disabling sock timestamp.

When SCTP accepts an association or peel one off, it copies sock flags
but forgot to call net_enable_timestamp() if a packet timestamping flag
was copied, leading to extra calls to net_disable_timestamp() whenever
such clones were closed.

The fix is to call net_enable_timestamp() whenever we copy a sock with
that flag on, like tcp does.
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: SK_FLAGS_TIMESTAMP is newly defined]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit d85242d9)
Signed-off-by: Willy Tarreau <w@1wt.eu>

include/net/sock.h

@@ -507,6 +507,8 @@ enum sock_flags {
 	SOCK_TIMESTAMPING_SYS_HARDWARE, /* %SOF_TIMESTAMPING_SYS_HARDWARE */
 };
 
+#define SK_FLAGS_TIMESTAMP ((1UL << SOCK_TIMESTAMP) | (1UL << SOCK_TIMESTAMPING_RX_SOFTWARE))
+
 static inline void sock_copy_flags(struct sock *nsk, struct sock *osk)
 {
 	nsk->sk_flags = osk->sk_flags;

net/sctp/socket.c

@@ -6756,6 +6756,9 @@ void sctp_copy_sock(struct sock *newsk, struct sock *sk,
 	newinet->mc_ttl = 1;
 	newinet->mc_index = 0;
 	newinet->mc_list = NULL;
+
+	if (newsk->sk_flags & SK_FLAGS_TIMESTAMP)
+		net_enable_timestamp();
 }
 
 /* Populate the fields of the newsk from the oldsk and migrate the assoc