[PATCH 3.2 041/140] net: ipv4: fix for a race condition in raw_sendmsg

[Ben Hutchings]

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

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

From: Mohamed Ghannam <simo.ghannam@xxxxxxxxx>

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@xxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.2:
 - flowi4 flags don't depend on hdrincl
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -484,11 +484,16 @@ 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.
 	 */
@@ -564,7 +569,7 @@ 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)
@@ -585,11 +590,11 @@ 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) | FLOWI_FLAG_CAN_SLEEP,
 			   daddr, saddr, 0, 0);
 
-	if (!inet->hdrincl) {
+	if (!hdrincl) {
 		rfv.iov = msg->msg_iov;
 		rfv.hlen = 0;
 
@@ -614,7 +619,7 @@ 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);