From d5d4a7b538b52db63927773a8905fcd9f78a42e2 Mon Sep 17 00:00:00 2001 From: Kyle Zeng Date: Mon, 10 Aug 2026 14:41:14 +0000 Subject: [PATCH] vxlan: keep the last remote linked during FDB flush A non-nexthop FDB entry is expected to have at least one remote while it remains reachable through the FDB hash table. A filtered bulk flush violates this invariant when every remote matches: It unlinks the last remote in vxlan_fdb_dst_destroy() and only afterwards tells vxlan_flush() to destroy the parent FDB entry. An RCU reader can find the parent during this interval. first_remote_rcu() then applies list_entry_rcu() to the empty list head, producing an invalid remote pointer that the receive learning path can read from and write to. When a matching remote is the sole remaining remote, leave it linked and ask the caller to destroy the entire FDB entry. vxlan_fdb_destroy() keeps the remote attached while sending the deletion notification and removing the parent from the lookup structures. Fixes: c499fccb71cb ("vxlan: vxlan_core: Support FDB flushing by destination VNI") Cc: stable@vger.kernel.org Signed-off-by: Kyle Zeng Co-developed-by: David Lee Signed-off-by: David Lee Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260810144115.821654-1-david.lee@trailofbits.com Signed-off-by: Jakub Kicinski --- drivers/net/vxlan/vxlan_core.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c index 824144bb7774..fbb6ddbb7f89 100644 --- a/drivers/net/vxlan/vxlan_core.c +++ b/drivers/net/vxlan/vxlan_core.c @@ -3058,18 +3058,19 @@ vxlan_fdb_flush_match_remotes(struct vxlan_fdb *f, struct vxlan_dev *vxlan, const struct vxlan_fdb_flush_desc *desc, bool *p_destroy_fdb) { - bool remotes_flushed = false; struct vxlan_rdst *rd, *tmp; list_for_each_entry_safe(rd, tmp, &f->remotes, list) { if (!vxlan_fdb_flush_remote_matches(desc, rd)) continue; - vxlan_fdb_dst_destroy(vxlan, f, rd, true); - remotes_flushed = true; - } + if (list_is_singular(&f->remotes)) { + *p_destroy_fdb = true; + return; + } - *p_destroy_fdb = remotes_flushed && list_empty(&f->remotes); + vxlan_fdb_dst_destroy(vxlan, f, rd, true); + } } /* Purge the forwarding table */