Re: [syzbot] [net?] KASAN: slab-use-after-free Write in __xfrm_state_delete

[Hillf Danton <hdanton@sina.com>]

> Date: Sun, 24 Aug 2025 12:21:23 -0700	[thread overview]
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    b1c92cdf5af3 Merge branch 'net-wangxun-complete-ethtool-co..
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1411b062580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=67b99ceb67d33475
> dashboard link: https://syzkaller.appspot.com/bug?extid=a25ee9d20d31e483ba7b
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14221862580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=159fba34580000

#syz test

--- x/net/xfrm/xfrm_state.c
+++ y/net/xfrm/xfrm_state.c
@@ -618,6 +618,8 @@ static void xfrm_state_gc_destroy(struct
 	xfrm_state_free(x);
 }
 
+static DEFINE_MUTEX(notify_mutex);
+
 static void xfrm_state_gc_task(struct work_struct *work)
 {
 	struct xfrm_state *x;
@@ -630,8 +632,10 @@ static void xfrm_state_gc_task(struct wo
 
 	synchronize_rcu();
 
+	mutex_lock(&notify_mutex);
 	hlist_for_each_entry_safe(x, tmp, &gc_list, gclist)
 		xfrm_state_gc_destroy(x);
+	mutex_unlock(&notify_mutex);
 }
 
 static enum hrtimer_restart xfrm_timer_handler(struct hrtimer *me)
@@ -921,6 +925,7 @@ int xfrm_state_flush(struct net *net, u8
 {
 	int i, err = 0, cnt = 0;
 
+	mutex_lock(&notify_mutex);
 	spin_lock_bh(&net->xfrm.xfrm_state_lock);
 	err = xfrm_state_flush_secctx_check(net, proto, task_valid);
 	if (err)
@@ -950,6 +955,7 @@ restart:
 	}
 out:
 	spin_unlock_bh(&net->xfrm.xfrm_state_lock);
+	mutex_unlock(&notify_mutex);
 	if (cnt)
 		err = 0;
 
--