ipv6: use READ_ONCE() for inet->hdrincl as in ipv4

BugLink: https://bugs.launchpad.net/bugs/1878246

commit 59e3e4b5 upstream.

As it was done in commit 8f659a03 ("net: ipv4: fix for a race
condition in raw_sendmsg") and commit 20b50d79 ("net: ipv4: emulate
READ_ONCE() on ->hdrincl bit-field in raw_sendmsg()") for ipv4, copy the
value of inet->hdrincl in a local variable, to avoid introducing a race
condition in the next commit.
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/ipv6/raw.c

@@ -764,6 +764,7 @@ static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	int hlimit = -1;
 	int tclass = -1;
 	int dontfrag = -1;
+	int hdrincl;
 	u16 proto;
 	int err;
 
@@ -777,6 +778,13 @@ static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	if (msg->msg_flags & MSG_OOB)
 		return -EOPNOTSUPP;
 
+	/* hdrincl should be READ_ONCE(inet->hdrincl)
+	 * but READ_ONCE() doesn't work with bit fields.
+	 * Doing this indirectly yields the same result.
+	 */
+	hdrincl = inet->hdrincl;
+	hdrincl = READ_ONCE(hdrincl);
+
 	/*
 	 *	Get and verify the address.
 	 */
@@ -885,7 +893,7 @@ static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		fl6.flowi6_oif = np->ucast_oif;
 	security_sk_classify_flow(sk, flowi6_to_flowi(&fl6));
 
-	if (inet->hdrincl)
+	if (hdrincl)
 		fl6.flowi6_flags |= FLOWI_FLAG_KNOWN_NH;
 
 	dst = ip6_dst_lookup_flow(sock_net(sk), sk, &fl6, final_p);
@@ -906,7 +914,7 @@ static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		goto do_confirm;
 
 back_from_confirm:
-	if (inet->hdrincl)
+	if (hdrincl)
 		err = rawv6_send_hdrinc(sk, msg, len, &fl6, &dst, msg->msg_flags);
 	else {
 		lock_sock(sk);