netdev - [PATCH net 2/5] net: ipv6: rpl_iptunnel: block BH in rpl_output() and rpl

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Message-ID: <20240531132636.2637995-3-edumazet@google.com>
Date: Fri, 31 May 2024 13:26:33 +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: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, Alexander Aring <aahringo@...hat.com>
Subject: [PATCH net 2/5] net: ipv6: rpl_iptunnel: block BH in rpl_output() and rpl_input()

As explained in commit 1378817486d6 ("tipc: block BH
before using dst_cache"), net/core/dst_cache.c
helpers need to be called with BH disabled.

Disabling preemption in rpl_output() is not good enough,
because rpl_output() is called from process context,
lwtunnel_output() only uses rcu_read_lock().

We might be interrupted by a softirq, re-enter rpl_output()
and corrupt dst_cache data structures.

Fix the race by using local_bh_disable() instead of
preempt_disable().

Apply a similar change in rpl_input().

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Alexander Aring <aahringo@...hat.com>
---
 net/ipv6/rpl_iptunnel.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/net/ipv6/rpl_iptunnel.c b/net/ipv6/rpl_iptunnel.c
index a013b92cbb860aa36a23f50d3d5c5963857d601c..2c83b7586422ddd2ae877f98e47698410e47b233 100644
--- a/net/ipv6/rpl_iptunnel.c
+++ b/net/ipv6/rpl_iptunnel.c
@@ -212,9 +212,9 @@ static int rpl_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 	if (unlikely(err))
 		goto drop;
 
-	preempt_disable();
+	local_bh_disable();
 	dst = dst_cache_get(&rlwt->cache);
-	preempt_enable();
+	local_bh_enable();
 
 	if (unlikely(!dst)) {
 		struct ipv6hdr *hdr = ipv6_hdr(skb);
@@ -234,9 +234,9 @@ static int rpl_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 			goto drop;
 		}
 
-		preempt_disable();
+		local_bh_disable();
 		dst_cache_set_ip6(&rlwt->cache, dst, &fl6.saddr);
-		preempt_enable();
+		local_bh_enable();
 	}
 
 	skb_dst_drop(skb);
@@ -268,23 +268,21 @@ static int rpl_input(struct sk_buff *skb)
 		return err;
 	}
 
-	preempt_disable();
+	local_bh_disable();
 	dst = dst_cache_get(&rlwt->cache);
-	preempt_enable();
 
 	if (!dst) {
 		ip6_route_input(skb);
 		dst = skb_dst(skb);
 		if (!dst->error) {
-			preempt_disable();
 			dst_cache_set_ip6(&rlwt->cache, dst,
 					  &ipv6_hdr(skb)->saddr);
-			preempt_enable();
 		}
 	} else {
 		skb_dst_drop(skb);
 		skb_dst_set(skb, dst);
 	}
+	local_bh_enable();
 
 	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
 	if (unlikely(err))
-- 
2.45.1.288.g0e0cd299f1-goog