netdev - [PATCH net v3 2/2] net: ipv6: fix dst ref loop on input in rpl lwt

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Message-Id: <20250225175139.25239-3-justin.iurman@uliege.be>
Date: Tue, 25 Feb 2025 18:51:39 +0100
From: Justin Iurman <justin.iurman@...ege.be>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	dsahern@...nel.org,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	justin.iurman@...ege.be,
	Alexander Aring <alex.aring@...il.com>,
	Ido Schimmel <idosch@...dia.com>
Subject: [PATCH net v3 2/2] net: ipv6: fix dst ref loop on input in rpl lwt

Prevent a dst ref loop on input in rpl_iptunnel.

Fixes: a7a29f9c361f ("net: ipv6: add rpl sr tunnel")
Cc: Alexander Aring <alex.aring@...il.com>
Cc: Ido Schimmel <idosch@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
Signed-off-by: Justin Iurman <justin.iurman@...ege.be>
---
 net/ipv6/rpl_iptunnel.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/rpl_iptunnel.c b/net/ipv6/rpl_iptunnel.c
index 0ac4283acdf2..7c05ac846646 100644
--- a/net/ipv6/rpl_iptunnel.c
+++ b/net/ipv6/rpl_iptunnel.c
@@ -262,10 +262,18 @@ static int rpl_input(struct sk_buff *skb)
 {
 	struct dst_entry *orig_dst = skb_dst(skb);
 	struct dst_entry *dst = NULL;
+	struct lwtunnel_state *lwtst;
 	struct rpl_lwt *rlwt;
 	int err;
 
-	rlwt = rpl_lwt_lwtunnel(orig_dst->lwtstate);
+	/* We cannot dereference "orig_dst" once ip6_route_input() or
+	 * skb_dst_drop() is called. However, in order to detect a dst loop, we
+	 * need the address of its lwtstate. So, save the address of lwtstate
+	 * now and use it later as a comparison.
+	 */
+	lwtst = orig_dst->lwtstate;
+
+	rlwt = rpl_lwt_lwtunnel(lwtst);
 
 	local_bh_disable();
 	dst = dst_cache_get(&rlwt->cache);
@@ -280,7 +288,9 @@ static int rpl_input(struct sk_buff *skb)
 	if (!dst) {
 		ip6_route_input(skb);
 		dst = skb_dst(skb);
-		if (!dst->error) {
+
+		/* cache only if we don't create a dst reference loop */
+		if (!dst->error && lwtst != dst->lwtstate) {
 			local_bh_disable();
 			dst_cache_set_ip6(&rlwt->cache, dst,
 					  &ipv6_hdr(skb)->saddr);
-- 
2.34.1