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@google.com>
Cc: Alexander Aring <aahringo@redhat.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Link: https://lore.kernel.org/r/20240531132636.2637995-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv6/rpl_iptunnel.c b/net/ipv6/rpl_iptunnel.c
index a013b92cbb860aa36a23f50d3d5c5963857d601c..2c83b7586422ddd2ae877f98e47698410e47b233 100644 (file)
--- 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))