[PATCH V1] xfrm: prevent policy_hthresh.work from racing with netns teardown
From: Tahera Fahimi <hidden>
Date: 2026-08-20 21:14:36
Also in:
lkml, stable
Subsystem:
networking [general], networking [ipsec], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Steffen Klassert, Herbert Xu, Linus Torvalds
[ Upstream commit 29fe3a61bcdce398ee3955101c39f89c01a8a77e ]
An XFRM_MSG_NEWSPDINFO request can queue the per-net work item
policy_hthresh.work onto the system workqueue. xfrm_hash_rebuild()
retrieves the enclosing struct net from the work item, so the callback
can dereference freed memory if it runs after net namespace teardown.
Upstream prevents this race with disable_work_sync(), which blocks new
queueing attempts and synchronizes pending or running work. Linux 6.6
does not provide that workqueue API, and cancel_work_sync() alone is not
sufficient because another request could queue the work after it returns.
Provide the same guarantee with an XFRM-local work_disabled flag. Protect
the flag and schedule_work() with the existing policy_hthresh seqlock so
teardown can atomically stop new queueing attempts. Then use
cancel_work_sync() to synchronize work that was queued before the flag was
set. This ensures policy_hthresh.work cannot outlive its struct net.
Fixes: 880a6fab8f6b ("xfrm: configure policy hash table thresholds by netlink")
Assisted-by: GitHub-Copilot:GPT-5.6 Sol
Signed-off-by: Tahera Fahimi <redacted>
Reviewed-by: Allen Pais <redacted>
---
include/net/netns/xfrm.h | 1 +
net/xfrm/xfrm_policy.c | 19 ++++++++++++++++++-
2 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/include/net/netns/xfrm.h b/include/net/netns/xfrm.h
index 423b52eca908d..99eb5c2ff888b 100644
--- a/include/net/netns/xfrm.h
+++ b/include/net/netns/xfrm.h@@ -23,6 +23,7 @@ struct xfrm_policy_hash { struct xfrm_policy_hthresh { struct work_struct work; seqlock_t lock; + bool work_disabled; u8 lbits4; u8 rbits4; u8 lbits6;
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 00d9693c13ae7..cc8f4d4b70875 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c@@ -1384,7 +1384,10 @@ static void xfrm_hash_rebuild(struct work_struct *work) void xfrm_policy_hash_rebuild(struct net *net) { - schedule_work(&net->xfrm.policy_hthresh.work); + write_seqlock(&net->xfrm.policy_hthresh.lock); + if (!net->xfrm.policy_hthresh.work_disabled) + schedule_work(&net->xfrm.policy_hthresh.work); + write_sequnlock(&net->xfrm.policy_hthresh.lock); } EXPORT_SYMBOL(xfrm_policy_hash_rebuild);
@@ -4181,6 +4184,7 @@ static int __net_init xfrm_policy_init(struct net *net) net->xfrm.policy_hthresh.rbits6 = 128; seqlock_init(&net->xfrm.policy_hthresh.lock); + net->xfrm.policy_hthresh.work_disabled = false; INIT_LIST_HEAD(&net->xfrm.policy_all); INIT_LIST_HEAD(&net->xfrm.inexact_bins);
@@ -4206,6 +4210,19 @@ static void xfrm_policy_fini(struct net *net) unsigned int sz; int dir; + /* Prevent new policy hash rebuilds before draining the work item. + * + * The upstream fix uses disable_work_sync(), which is unavailable + * in v6.6. Protecting work_disabled and schedule_work() with the + * same seqlock closes the check-to-queue race, while the subsequent + * cancel_work_sync() drains work that was queued or running before + * teardown disabled it. + */ + write_seqlock(&net->xfrm.policy_hthresh.lock); + net->xfrm.policy_hthresh.work_disabled = true; + write_sequnlock(&net->xfrm.policy_hthresh.lock); + cancel_work_sync(&net->xfrm.policy_hthresh.work); + flush_work(&net->xfrm.policy_hash_work); #ifdef CONFIG_XFRM_SUB_POLICY xfrm_policy_flush(net, XFRM_POLICY_TYPE_SUB, false);
--
2.43.0