queue-6.19/seg6-separate-dst_cache-for-input-and-output-paths-in-seg6-lwtunnel.patch

From c3812651b522fe8437ebb7063b75ddb95b571643 Mon Sep 17 00:00:00 2001
From: Andrea Mayer <andrea.mayer@uniroma2.it>
Date: Sat, 4 Apr 2026 02:44:04 +0200
Subject: seg6: separate dst_cache for input and output paths in seg6 lwtunnel

From: Andrea Mayer <andrea.mayer@uniroma2.it>

commit c3812651b522fe8437ebb7063b75ddb95b571643 upstream.

The seg6 lwtunnel uses a single dst_cache per encap route, shared
between seg6_input_core() and seg6_output_core(). These two paths
can perform the post-encap SID lookup in different routing contexts
(e.g., ip rules matching on the ingress interface, or VRF table
separation). Whichever path runs first populates the cache, and the
other reuses it blindly, bypassing its own lookup.

Fix this by splitting the cache into cache_input and cache_output,
so each path maintains its own cached dst independently.

Fixes: 6c8702c60b88 ("ipv6: sr: add support for SRH encapsulation and injection with lwtunnels")
Cc: stable@vger.kernel.org
Signed-off-by: Andrea Mayer <andrea.mayer@uniroma2.it>
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: Justin Iurman <justin.iurman@gmail.com>
Link: https://patch.msgid.link/20260404004405.4057-2-andrea.mayer@uniroma2.it
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/seg6_iptunnel.c |   34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

--- a/net/ipv6/seg6_iptunnel.c
+++ b/net/ipv6/seg6_iptunnel.c
@@ -48,7 +48,8 @@ static size_t seg6_lwt_headroom(struct s
 }
 
 struct seg6_lwt {
-	struct dst_cache cache;
+	struct dst_cache cache_input;
+	struct dst_cache cache_output;
 	struct seg6_iptunnel_encap tuninfo[];
 };
 
@@ -488,7 +489,7 @@ static int seg6_input_core(struct net *n
 	slwt = seg6_lwt_lwtunnel(lwtst);
 
 	local_bh_disable();
-	dst = dst_cache_get(&slwt->cache);
+	dst = dst_cache_get(&slwt->cache_input);
 	local_bh_enable();
 
 	err = seg6_do_srh(skb, dst);
@@ -504,7 +505,7 @@ static int seg6_input_core(struct net *n
 		/* cache only if we don't create a dst reference loop */
 		if (!dst->error && lwtst != dst->lwtstate) {
 			local_bh_disable();
-			dst_cache_set_ip6(&slwt->cache, dst,
+			dst_cache_set_ip6(&slwt->cache_input, dst,
 					  &ipv6_hdr(skb)->saddr);
 			local_bh_enable();
 		}
@@ -564,7 +565,7 @@ static int seg6_output_core(struct net *
 	slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);
 
 	local_bh_disable();
-	dst = dst_cache_get(&slwt->cache);
+	dst = dst_cache_get(&slwt->cache_output);
 	local_bh_enable();
 
 	err = seg6_do_srh(skb, dst);
@@ -591,7 +592,7 @@ static int seg6_output_core(struct net *
 		/* cache only if we don't create a dst reference loop */
 		if (orig_dst->lwtstate != dst->lwtstate) {
 			local_bh_disable();
-			dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
+			dst_cache_set_ip6(&slwt->cache_output, dst, &fl6.saddr);
 			local_bh_enable();
 		}
 
@@ -701,11 +702,13 @@ static int seg6_build_state(struct net *
 
 	slwt = seg6_lwt_lwtunnel(newts);
 
-	err = dst_cache_init(&slwt->cache, GFP_ATOMIC);
-	if (err) {
-		kfree(newts);
-		return err;
-	}
+	err = dst_cache_init(&slwt->cache_input, GFP_ATOMIC);
+	if (err)
+		goto err_free_newts;
+
+	err = dst_cache_init(&slwt->cache_output, GFP_ATOMIC);
+	if (err)
+		goto err_destroy_input;
 
 	memcpy(&slwt->tuninfo, tuninfo, tuninfo_len);
 
@@ -720,11 +723,20 @@ static int seg6_build_state(struct net *
 	*ts = newts;
 
 	return 0;
+
+err_destroy_input:
+	dst_cache_destroy(&slwt->cache_input);
+err_free_newts:
+	kfree(newts);
+	return err;
 }
 
 static void seg6_destroy_state(struct lwtunnel_state *lwt)
 {
-	dst_cache_destroy(&seg6_lwt_lwtunnel(lwt)->cache);
+	struct seg6_lwt *slwt = seg6_lwt_lwtunnel(lwt);
+
+	dst_cache_destroy(&slwt->cache_input);
+	dst_cache_destroy(&slwt->cache_output);
 }
 
 static int seg6_fill_encap_info(struct sk_buff *skb,