[SRU][J][PATCH 1/1] net: decrease cached dst counters in dst_release

[Cengiz Can]

From: Antoine Tenart <atenart at kernel.org>

Upstream fix ac888d58869b ("net: do not delay dst_entries_add() in
dst_release()") moved decrementing the dst count from dst_destroy to
dst_release to avoid accessing already freed data in case of netns
dismantle. However in case CONFIG_DST_CACHE is enabled and OvS+tunnels
are used, this fix is incomplete as the same issue will be seen for
cached dsts:

  Unable to handle kernel paging request at virtual address ffff5aabf6b5c000
  Call trace:
   percpu_counter_add_batch+0x3c/0x160 (P)
   dst_release+0xec/0x108
   dst_cache_destroy+0x68/0xd8
   dst_destroy+0x13c/0x168
   dst_destroy_rcu+0x1c/0xb0
   rcu_do_batch+0x18c/0x7d0
   rcu_core+0x174/0x378
   rcu_core_si+0x18/0x30

Fix this by invalidating the cache, and thus decrementing cached dst
counters, in dst_release too.

Fixes: d71785ffc7e7 ("net: add dst_cache to ovs vxlan lwtunnel")
Signed-off-by: Antoine Tenart <atenart at kernel.org>
Link: https://patch.msgid.link/20250326173634.31096-1-atenart@kernel.org
Signed-off-by: Paolo Abeni <pabeni at redhat.com>
(backported from commit 3a0a3ff6593d670af2451ec363ccb7b18aec0c0a)
[bot_kybele: Inserted the CONFIG_DST_CACHE reset block into this tree's older
 atomic_dec_return-based dst_release (inside the `if (!newrefcnt)` branch using
 call_rcu), since this tree predates the rcuref_put/call_rcu_hurry rewrite.]
CVE-2025-22057
Assisted-by: kybele:claude-opus-4.8
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 net/core/dst.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/core/dst.c b/net/core/dst.c
index 6d74b4663085..c1ea331c4bfd 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -173,6 +173,14 @@ void dst_release(struct dst_entry *dst)
 			net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
 					     __func__, dst, newrefcnt);
 		if (!newrefcnt){
+#ifdef CONFIG_DST_CACHE
+			if (dst->flags & DST_METADATA) {
+				struct metadata_dst *md_dst = (struct metadata_dst *)dst;
+
+				if (md_dst->type == METADATA_IP_TUNNEL)
+					dst_cache_reset_now(&md_dst->u.tun_info.dst_cache);
+			}
+#endif
 			dst_count_dec(dst);
 			call_rcu(&dst->rcu_head, dst_destroy_rcu);
 		}
-- 
2.53.0