[PATCH 6.6 244/567] netfilter: xt_IDLETIMER: reject rev0 reuse of ALARM timer labels

Greg Kroah-Hartman
2026-03-23T15:03:54Z

6.6-stable review patch. If anyone has any objections, please let me know.

------------------

From: Yuan Tan <tanyuan98@outlook.com>

[ Upstream commit 329f0b9b48ee6ab59d1ab72fef55fe8c6463a6cf ]

IDLETIMER revision 0 rules reuse existing timers by label and always call
mod_timer() on timer->timer.

If the label was created first by revision 1 with XT_IDLETIMER_ALARM,
the object uses alarm timer semantics and timer->timer is never initialized.
Reusing that object from revision 0 causes mod_timer() on an uninitialized
timer_list, triggering debugobjects warnings and possible panic when
panic_on_warn=1.

Fix this by rejecting revision 0 rule insertion when an existing timer with
the same label is of ALARM type.

Fixes: 68983a354a65 ("netfilter: xtables: Add snapshot of hardidletimer target")
Co-developed-by: Yifan Wu <yifanwucs@gmail.com>
Signed-off-by: Yifan Wu <yifanwucs@gmail.com>
Co-developed-by: Juefei Pu <tomapufckgml@gmail.com>
Signed-off-by: Juefei Pu <tomapufckgml@gmail.com>
Signed-off-by: Yuan Tan <tanyuan98@outlook.com>
Signed-off-by: Xin Liu <dstsmallbird@foxmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/xt_IDLETIMER.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/net/netfilter/xt_IDLETIMER.c b/net/netfilter/xt_IDLETIMER.c
index 9869ef3c2ab37..92a8289b1cb35 100644
--- a/net/netfilter/xt_IDLETIMER.c
+++ b/net/netfilter/xt_IDLETIMER.c
@@ -320,6 +320,12 @@ static int idletimer_tg_checkentry(const struct xt_tgchk_param *par)

info->timer = __idletimer_tg_find_by_label(info->label);
if (info->timer) {
+ if (info->timer->timer_type & XT_IDLETIMER_ALARM) {
+ pr_debug("Adding/Replacing rule with same label and different timer type is not allowed\n");
+ mutex_unlock(&list_mutex);
+ return -EINVAL;
+ }
+
info->timer->refcnt++;
mod_timer(&info->timer->timer,
msecs_to_jiffies(info->timeout * 1000) + jiffies);
--
2.51.0