[PATCH AUTOSEL 5.10 08/13] net: ipv6: rpl_iptunnel: block BH in rpl_output() and rpl_input()

[Sasha Levin]

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit db0090c6eb12c31246438b7fe2a8f1b833e7a653 ]

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@xxxxxxxxxx>
Cc: Alexander Aring <aahringo@xxxxxxxxxx>
Acked-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240531132636.2637995-3-edumazet@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 5fdf3ebb953fb..2ba605db69769 100644
--- a/net/ipv6/rpl_iptunnel.c
+++ b/net/ipv6/rpl_iptunnel.c
@@ -217,9 +217,9 @@ 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);
@@ -239,9 +239,9 @@ 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);
@@ -273,9 +273,8 @@ static int rpl_input(struct sk_buff *skb)
 		return err;
 	}
 
-	preempt_disable();
+	local_bh_disable();
 	dst = dst_cache_get(&rlwt->cache);
-	preempt_enable();
 
 	skb_dst_drop(skb);
 
@@ -283,14 +282,13 @@ static int rpl_input(struct sk_buff *skb)
 		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_set(skb, dst);
 	}
+	local_bh_enable();
 
 	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
 	if (unlikely(err))
-- 
2.43.0