netdev - [PATCH net 3/4] ipv6: fix possible infinite loop in fib6_info_uses

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Message-ID: <20250725140725.3626540-4-edumazet@google.com>
Date: Fri, 25 Jul 2025 14:07:24 +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 3/4] ipv6: fix possible infinite loop in fib6_info_uses_dev()

fib6_info_uses_dev() seems to rely on RCU without an explicit
protection.

Like the prior fix in rt6_nlmsg_size(),
we need to make sure fib6_del_route() or fib6_add_rt2node()
have not removed the anchor from the list, or we risk an infinite loop.

Fixes: d9ccb18f83ea ("ipv6: Fix soft lockups in fib6_select_path under high next hop churn")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv6/route.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 6d4e147ae46bc245ccd195e5fb0e254f34ec65a4..04f2b860ca6156776e0cedd18d96877effd287a4 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -5958,16 +5958,21 @@ static bool fib6_info_uses_dev(const struct fib6_info *f6i,
 	if (f6i->fib6_nh->fib_nh_dev == dev)
 		return true;
 
-	if (f6i->fib6_nsiblings) {
-		struct fib6_info *sibling, *next_sibling;
+	if (READ_ONCE(f6i->fib6_nsiblings)) {
+		const struct fib6_info *sibling;
 
-		list_for_each_entry_safe(sibling, next_sibling,
-					 &f6i->fib6_siblings, fib6_siblings) {
-			if (sibling->fib6_nh->fib_nh_dev == dev)
+		rcu_read_lock();
+		list_for_each_entry_rcu(sibling, &f6i->fib6_siblings,
+					fib6_siblings) {
+			if (sibling->fib6_nh->fib_nh_dev == dev) {
+				rcu_read_unlock();
 				return true;
+			}
+			if (!READ_ONCE(f6i->fib6_nsiblings))
+				break;
 		}
+		rcu_read_unlock();
 	}
-
 	return false;
 }
 
-- 
2.50.1.470.g6ba607880d-goog