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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Olivier Matz <olivier.matz@6wind.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.4 17/18] ipv6: use READ_ONCE() for inet->hdrincl as in ipv4
Date:   Mon,  4 May 2020 19:57:15 +0200
Message-Id: <20200504165445.162621760@linuxfoundation.org>
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From: Olivier Matz <olivier.matz@6wind.com>

commit 59e3e4b52663a9d97efbce7307f62e4bc5c9ce91 upstream.

As it was done in commit 8f659a03a0ba ("net: ipv4: fix for a race
condition in raw_sendmsg") and commit 20b50d79974e ("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>

---
 net/ipv6/raw.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -757,6 +757,7 @@ static int rawv6_sendmsg(struct sock *sk
 	int hlimit = -1;
 	int tclass = -1;
 	int dontfrag = -1;
+	int hdrincl;
 	u16 proto;
 	int err;
 
@@ -770,6 +771,13 @@ static int rawv6_sendmsg(struct sock *sk
 	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.
 	 */
@@ -878,7 +886,7 @@ static int rawv6_sendmsg(struct sock *sk
 		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(sk, &fl6, final_p);
@@ -899,7 +907,7 @@ static int rawv6_sendmsg(struct sock *sk
 		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);