linux-kernel - [PATCH 3.16 088/254] net: ipv4: fix for a race condition in raw

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Message-ID: <lsq.1519831218.973234790@decadent.org.uk>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Mohamed Ghannam" <simo.ghannam@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>
Subject: [PATCH 3.16 088/254] net: ipv4: fix for a race condition in
 raw_sendmsg

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mohamed Ghannam <simo.ghannam@...il.com>

commit 8f659a03a0ba9289b9aeb9b4470e6fb263d6f483 upstream.

inet->hdrincl is racy, and could lead to uninitialized stack pointer
usage, so its value should be read only once.

Fixes: c008ba5bdc9f ("ipv4: Avoid reading user iov twice after raw_probe_proto_opt")
Signed-off-by: Mohamed Ghannam <simo.ghannam@...il.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/ipv4/raw.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -490,11 +490,16 @@ static int raw_sendmsg(struct kiocb *ioc
 	int err;
 	struct ip_options_data opt_copy;
 	struct raw_frag_vec rfv;
+	int hdrincl;
 
 	err = -EMSGSIZE;
 	if (len > 0xFFFF)
 		goto out;
 
+	/* hdrincl should be READ_ONCE(inet->hdrincl)
+	 * but READ_ONCE() doesn't work with bit fields
+	 */
+	hdrincl = inet->hdrincl;
 	/*
 	 *	Check the flags.
 	 */
@@ -569,7 +574,7 @@ static int raw_sendmsg(struct kiocb *ioc
 		/* Linux does not mangle headers on raw sockets,
 		 * so that IP options + IP_HDRINCL is non-sense.
 		 */
-		if (inet->hdrincl)
+		if (hdrincl)
 			goto done;
 		if (ipc.opt->opt.srr) {
 			if (!daddr)
@@ -591,12 +596,12 @@ static int raw_sendmsg(struct kiocb *ioc
 
 	flowi4_init_output(&fl4, ipc.oif, sk->sk_mark, tos,
 			   RT_SCOPE_UNIVERSE,
-			   inet->hdrincl ? IPPROTO_RAW : sk->sk_protocol,
+			   hdrincl ? IPPROTO_RAW : sk->sk_protocol,
 			   inet_sk_flowi_flags(sk) |
-			    (inet->hdrincl ? FLOWI_FLAG_KNOWN_NH : 0),
+			    (hdrincl ? FLOWI_FLAG_KNOWN_NH : 0),
 			   daddr, saddr, 0, 0);
 
-	if (!inet->hdrincl) {
+	if (!hdrincl) {
 		rfv.iov = msg->msg_iov;
 		rfv.hlen = 0;
 
@@ -621,7 +626,7 @@ static int raw_sendmsg(struct kiocb *ioc
 		goto do_confirm;
 back_from_confirm:
 
-	if (inet->hdrincl)
+	if (hdrincl)
 		err = raw_send_hdrinc(sk, &fl4, msg->msg_iov, len,
 				      &rt, msg->msg_flags);