netdev - [PATCH net 4/4] ipv6: annotate data-races around rt->fib6

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Message-ID: <20250725140725.3626540-5-edumazet@google.com>
Date: Fri, 25 Jul 2025 14:07:25 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, David Ahern <dsahern@...nel.org>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net 4/4] ipv6: annotate data-races around rt->fib6_nsiblings

rt->fib6_nsiblings can be read locklessly, add corresponding
READ_ONCE() and WRITE_ONCE() annotations.

Fixes: 66f5d6ce53e6 ("ipv6: replace rwlock with rcu and spinlock in fib6_table")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv6/ip6_fib.c | 20 +++++++++++++-------
 net/ipv6/route.c   |  5 +++--
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index af7db69d9eac97033fde46c5ee57e0cfb53a36db..4d68bd853dbae92a48a15eeee091bfdde3b5c77d 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -445,15 +445,17 @@ struct fib6_dump_arg {
 static int fib6_rt_dump(struct fib6_info *rt, struct fib6_dump_arg *arg)
 {
 	enum fib_event_type fib_event = FIB_EVENT_ENTRY_REPLACE;
+	unsigned int nsiblings;
 	int err;
 
 	if (!rt || rt == arg->net->ipv6.fib6_null_entry)
 		return 0;
 
-	if (rt->fib6_nsiblings)
+	nsiblings = READ_ONCE(rt->fib6_nsiblings);
+	if (nsiblings)
 		err = call_fib6_multipath_entry_notifier(arg->nb, fib_event,
 							 rt,
-							 rt->fib6_nsiblings,
+							 nsiblings,
 							 arg->extack);
 	else
 		err = call_fib6_entry_notifier(arg->nb, fib_event, rt,
@@ -1138,7 +1140,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,
 
 			if (rt6_duplicate_nexthop(iter, rt)) {
 				if (rt->fib6_nsiblings)
-					rt->fib6_nsiblings = 0;
+					WRITE_ONCE(rt->fib6_nsiblings, 0);
 				if (!(iter->fib6_flags & RTF_EXPIRES))
 					return -EEXIST;
 				if (!(rt->fib6_flags & RTF_EXPIRES)) {
@@ -1167,7 +1169,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,
 			 */
 			if (rt_can_ecmp &&
 			    rt6_qualify_for_ecmp(iter))
-				rt->fib6_nsiblings++;
+				WRITE_ONCE(rt->fib6_nsiblings,
+					   rt->fib6_nsiblings + 1);
 		}
 
 		if (iter->fib6_metric > rt->fib6_metric)
@@ -1217,7 +1220,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,
 		fib6_nsiblings = 0;
 		list_for_each_entry_safe(sibling, temp_sibling,
 					 &rt->fib6_siblings, fib6_siblings) {
-			sibling->fib6_nsiblings++;
+			WRITE_ONCE(sibling->fib6_nsiblings,
+				   sibling->fib6_nsiblings + 1);
 			BUG_ON(sibling->fib6_nsiblings != rt->fib6_nsiblings);
 			fib6_nsiblings++;
 		}
@@ -1264,7 +1268,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,
 				list_for_each_entry_safe(sibling, next_sibling,
 							 &rt->fib6_siblings,
 							 fib6_siblings)
-					sibling->fib6_nsiblings--;
+					WRITE_ONCE(sibling->fib6_nsiblings,
+						   sibling->fib6_nsiblings - 1);
 				WRITE_ONCE(rt->fib6_nsiblings, 0);
 				list_del_rcu(&rt->fib6_siblings);
 				rcu_read_lock();
@@ -2014,7 +2019,8 @@ static void fib6_del_route(struct fib6_table *table, struct fib6_node *fn,
 			notify_del = true;
 		list_for_each_entry_safe(sibling, next_sibling,
 					 &rt->fib6_siblings, fib6_siblings)
-			sibling->fib6_nsiblings--;
+			WRITE_ONCE(sibling->fib6_nsiblings,
+				   sibling->fib6_nsiblings - 1);
 		WRITE_ONCE(rt->fib6_nsiblings, 0);
 		list_del_rcu(&rt->fib6_siblings);
 		rt6_multipath_rebalance(next_sibling);
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 04f2b860ca6156776e0cedd18d96877effd287a4..aaedc08607c01c409276032b3ac213bb1876c726 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -5346,7 +5346,8 @@ static void ip6_route_mpath_notify(struct fib6_info *rt,
 	 */
 	rcu_read_lock();
 
-	if ((nlflags & NLM_F_APPEND) && rt_last && rt_last->fib6_nsiblings) {
+	if ((nlflags & NLM_F_APPEND) && rt_last &&
+	    READ_ONCE(rt_last->fib6_nsiblings)) {
 		rt = list_first_or_null_rcu(&rt_last->fib6_siblings,
 					    struct fib6_info,
 					    fib6_siblings);
@@ -5856,7 +5857,7 @@ static int rt6_fill_node(struct net *net, struct sk_buff *skb,
 		if (dst->lwtstate &&
 		    lwtunnel_fill_encap(skb, dst->lwtstate, RTA_ENCAP, RTA_ENCAP_TYPE) < 0)
 			goto nla_put_failure;
-	} else if (rt->fib6_nsiblings) {
+	} else if (READ_ONCE(rt->fib6_nsiblings)) {
 		struct fib6_info *sibling;
 		struct nlattr *mp;
 
-- 
2.50.1.470.g6ba607880d-goog