[PATCH 5/8] xfrm: avoid lock inversion in nat keepalive work
From: Steffen Klassert <steffen.klassert@secunet.com>
Date: 2026-07-29 06:50:42
Subsystem:
networking [general], networking [ipsec], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Steffen Klassert, Herbert Xu, Linus Torvalds
From: Zihan Xi <redacted>
nat_keepalive_work() walks the state table while xfrm_state_walk()
holds net->xfrm.xfrm_state_lock. Its callback then acquires x->lock,
which conflicts with the delete path taking the same locks in reverse
order via xfrm_state_delete() and __xfrm_state_delete(). This creates
an AB-BA deadlock that is reported by lockdep when a NAT keepalive
worker races with SA deletion.
Fix this by splitting the keepalive walk into two phases. First,
collect the candidate states while the walk holds xfrm_state_lock and
take a reference on each state. Then, after the walk completes, process
each collected state and acquire x->lock without nesting it under
xfrm_state_lock.
Fixes: f531d13bdfe3 ("xfrm: support sending NAT keepalives in ESP in UDP states")
Cc: stable@vger.kernel.org
Reported-by: Vega <redacted>
Assisted-by: Codex:gpt-5.4
Signed-off-by: Zihan Xi <redacted>
Signed-off-by: Ren Wei <redacted>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
net/xfrm/xfrm_nat_keepalive.c | 57 +++++++++++++++++++++++++++++------
1 file changed, 48 insertions(+), 9 deletions(-)
diff --git a/net/xfrm/xfrm_nat_keepalive.c b/net/xfrm/xfrm_nat_keepalive.c
index eb1b6f67739e..8679c68c10a1 100644
--- a/net/xfrm/xfrm_nat_keepalive.c
+++ b/net/xfrm/xfrm_nat_keepalive.c@@ -156,24 +156,51 @@ static void nat_keepalive_send(struct nat_keepalive *ka) } struct nat_keepalive_work_ctx { + struct list_head states; time64_t next_run; time64_t now; }; -static int nat_keepalive_work_single(struct xfrm_state *x, int count, void *ptr) +struct nat_keepalive_state { + struct list_head list; + struct xfrm_state *x; +}; + +static int nat_keepalive_work_collect(struct xfrm_state *x, int count, void *ptr) { struct nat_keepalive_work_ctx *ctx = ptr; + struct nat_keepalive_state *state; + + if (!READ_ONCE(x->nat_keepalive_interval)) + return 0; + + state = kmalloc_obj(*state, GFP_ATOMIC); + if (!state) + return -ENOMEM; + + xfrm_state_hold(x); + state->x = x; + list_add_tail(&state->list, &ctx->states); + return 0; +} + +static void nat_keepalive_work_single(struct xfrm_state *x, + struct nat_keepalive_work_ctx *ctx) +{ bool send_keepalive = false; struct nat_keepalive ka; - time64_t next_run; + time64_t next_run = 0; u32 interval; int delta; + spin_lock_bh(&x->lock); + + if (x->km.state == XFRM_STATE_DEAD) + goto out; + interval = x->nat_keepalive_interval; if (!interval) - return 0; - - spin_lock(&x->lock); + goto out; delta = (int)(ctx->now - x->lastused); if (delta < interval) {
@@ -187,29 +214,41 @@ static int nat_keepalive_work_single(struct xfrm_state *x, int count, void *ptr) send_keepalive = true; } - spin_unlock(&x->lock); +out: + spin_unlock_bh(&x->lock); if (send_keepalive) nat_keepalive_send(&ka); - if (!ctx->next_run || next_run < ctx->next_run) + if (next_run && (!ctx->next_run || next_run < ctx->next_run)) ctx->next_run = next_run; - return 0; } static void nat_keepalive_work(struct work_struct *work) { + struct nat_keepalive_state *state, *tmp; struct nat_keepalive_work_ctx ctx; struct xfrm_state_walk walk; struct net *net; + int err; + INIT_LIST_HEAD(&ctx.states); ctx.next_run = 0; ctx.now = ktime_get_real_seconds(); net = container_of(work, struct net, xfrm.nat_keepalive_work.work); xfrm_state_walk_init(&walk, IPPROTO_ESP, NULL); - xfrm_state_walk(net, &walk, nat_keepalive_work_single, &ctx); + err = xfrm_state_walk(net, &walk, nat_keepalive_work_collect, &ctx); xfrm_state_walk_done(&walk, net); + list_for_each_entry_safe(state, tmp, &ctx.states, list) { + nat_keepalive_work_single(state->x, &ctx); + xfrm_state_put(state->x); + kfree(state); + } + if (err == -ENOMEM) { + schedule_delayed_work(&net->xfrm.nat_keepalive_work, 0); + return; + } if (ctx.next_run) schedule_delayed_work(&net->xfrm.nat_keepalive_work, (ctx.next_run - ctx.now) * HZ);
--
2.43.0