linux-kernel - Re: [syzbot] [net?] KASAN: slab-use-after-free Write in __xfrm_state

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Message-ID: <20250827004037.5728-1-hdanton@sina.com>
Date: Wed, 27 Aug 2025 08:40:36 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+a25ee9d20d31e483ba7b@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] KASAN: slab-use-after-free Write in __xfrm_state_delete

> 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/include/net/xfrm.h
+++ y/include/net/xfrm.h
@@ -202,6 +202,7 @@ struct xfrm_state {
 
 	refcount_t		refcnt;
 	spinlock_t		lock;
+	int deleted;
 
 	u32			pcpu_num;
 	struct xfrm_id		id;
--- x/net/xfrm/xfrm_state.c
+++ y/net/xfrm/xfrm_state.c
@@ -615,6 +615,7 @@ static void xfrm_state_gc_destroy(struct
 		put_page(x->xfrag.page);
 	xfrm_dev_state_free(x);
 	security_xfrm_state_free(x);
+	xfrm_state_delete(x);
 	xfrm_state_free(x);
 }
 
@@ -812,10 +813,16 @@ int __xfrm_state_delete(struct xfrm_stat
 	struct net *net = xs_net(x);
 	int err = -ESRCH;
 
-	if (x->km.state != XFRM_STATE_DEAD) {
-		x->km.state = XFRM_STATE_DEAD;
+	for (;;) {
+		if (x->km.state != XFRM_STATE_DEAD)
+			x->km.state = XFRM_STATE_DEAD;
 
 		spin_lock(&net->xfrm.xfrm_state_lock);
+		if (x->deleted) {
+			spin_unlock(&net->xfrm.xfrm_state_lock);
+			return 0;
+		}
+		x->deleted++;
 		list_del(&x->km.all);
 		hlist_del_rcu(&x->bydst);
 		hlist_del_rcu(&x->bysrc);
--