[PATCH v3 net-next 02/15] ipmr: Annotate access to mrt->mroute_do_{pim,assert,wrvifwhole}.

[Kuniyuki Iwashima <kuniyu@google.com>]

These fields in struct mr_table are updated in ip_mroute_setsockopt()
under RTNL:

  * mroute_do_pim
  * mroute_do_assert
  * mroute_do_wrvifwhole

However, ip_mroute_getsockopt() does not hold RTNL and read the first
two fields locklessly, and ip_mr_forward() reads all the three under
RCU.  pim_rcv_v1() also reads mroute_do_pim locklessly.

Let's use WRITE_ONCE() and READ_ONCE() for them.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
---
v3: Use READ_ONCE() for mrt->mroute_do_pim in ip_mr_forward()
     and pim_rcv_v1()
---
 net/ipv4/ipmr.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 131382c388e9..970f173654c7 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1506,7 +1506,7 @@ int ip_mroute_setsockopt(struct sock *sk, int optname, sockptr_t optval,
 			ret = -EFAULT;
 			break;
 		}
-		mrt->mroute_do_assert = val;
+		WRITE_ONCE(mrt->mroute_do_assert, val);
 		break;
 	case MRT_PIM:
 		if (!ipmr_pimsm_enabled()) {
@@ -1525,9 +1525,9 @@ int ip_mroute_setsockopt(struct sock *sk, int optname, sockptr_t optval,
 		do_wrvifwhole = (val == IGMPMSG_WRVIFWHOLE);
 		val = !!val;
 		if (val != mrt->mroute_do_pim) {
-			mrt->mroute_do_pim = val;
-			mrt->mroute_do_assert = val;
-			mrt->mroute_do_wrvifwhole = do_wrvifwhole;
+			WRITE_ONCE(mrt->mroute_do_pim, val);
+			WRITE_ONCE(mrt->mroute_do_assert, val);
+			WRITE_ONCE(mrt->mroute_do_wrvifwhole, do_wrvifwhole);
 		}
 		break;
 	case MRT_TABLE:
@@ -1610,10 +1610,10 @@ int ip_mroute_getsockopt(struct sock *sk, int optname, sockptr_t optval,
 	case MRT_PIM:
 		if (!ipmr_pimsm_enabled())
 			return -ENOPROTOOPT;
-		val = mrt->mroute_do_pim;
+		val = READ_ONCE(mrt->mroute_do_pim);
 		break;
 	case MRT_ASSERT:
-		val = mrt->mroute_do_assert;
+		val = READ_ONCE(mrt->mroute_do_assert);
 		break;
 	default:
 		return -ENOPROTOOPT;
@@ -2037,20 +2037,20 @@ static void ip_mr_forward(struct net *net, struct mr_table *mrt,
 
 		atomic_long_inc(&c->_c.mfc_un.res.wrong_if);
 
-		if (true_vifi >= 0 && mrt->mroute_do_assert &&
+		if (true_vifi >= 0 && READ_ONCE(mrt->mroute_do_assert) &&
 		    /* pimsm uses asserts, when switching from RPT to SPT,
 		     * so that we cannot check that packet arrived on an oif.
 		     * It is bad, but otherwise we would need to move pretty
 		     * large chunk of pimd to kernel. Ough... --ANK
 		     */
-		    (mrt->mroute_do_pim ||
+		    (READ_ONCE(mrt->mroute_do_pim) ||
 		     c->_c.mfc_un.res.ttls[true_vifi] < 255) &&
 		    time_after(jiffies,
 			       c->_c.mfc_un.res.last_assert +
 			       MFC_ASSERT_THRESH)) {
 			c->_c.mfc_un.res.last_assert = jiffies;
 			ipmr_cache_report(mrt, skb, true_vifi, IGMPMSG_WRONGVIF);
-			if (mrt->mroute_do_wrvifwhole)
+			if (READ_ONCE(mrt->mroute_do_wrvifwhole))
 				ipmr_cache_report(mrt, skb, true_vifi,
 						  IGMPMSG_WRVIFWHOLE);
 		}
@@ -2358,7 +2358,7 @@ int pim_rcv_v1(struct sk_buff *skb)
 	mrt = ipmr_rt_fib_lookup(net, skb);
 	if (IS_ERR(mrt))
 		goto drop;
-	if (!mrt->mroute_do_pim ||
+	if (!READ_ONCE(mrt->mroute_do_pim) ||
 	    pim->group != PIM_V1_VERSION || pim->code != PIM_V1_REGISTER)
 		goto drop;
 
-- 
2.53.0.473.g4a7958ca14-goog