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

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Message-ID: <tencent_85C67489962ECA2EE44C9D67DE46C912F006@qq.com>
Date: Wed, 27 Aug 2025 17:35:09 +0800
From: Edward Adam Davis <eadavis@...com>
To: 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

#syz test

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index f3014e4f54fc..a1d5acd1f2ad 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -229,6 +229,7 @@ struct xfrm_state {
 		int		trailer_len;
 		u32		extra_flags;
 		struct xfrm_mark	smark;
+		u8		alive;
 	} props;
 
 	struct xfrm_lifetime_cfg lft;
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 78fcbb89cf32..d66adf7ee6a2 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -755,6 +755,7 @@ struct xfrm_state *xfrm_state_alloc(struct net *net)
 		x->pcpu_num = UINT_MAX;
 		spin_lock_init(&x->lock);
 		x->mode_data = NULL;
+		x->props.alive = 1;
 	}
 	return x;
 }
@@ -830,6 +831,7 @@ int __xfrm_state_delete(struct xfrm_state *x)
 			hlist_del_rcu(&x->byspi);
 		net->xfrm.state_num--;
 		xfrm_nat_keepalive_state_updated(x);
+		x->props.alive = 0;
 		spin_unlock(&net->xfrm.xfrm_state_lock);
 
 		xfrm_dev_state_delete(x);
@@ -932,7 +934,8 @@ int xfrm_state_flush(struct net *net, u8 proto, bool task_valid)
 restart:
 		hlist_for_each_entry(x, net->xfrm.state_bydst+i, bydst) {
 			if (!xfrm_state_kern(x) &&
-			    xfrm_id_proto_match(x->id.proto, proto)) {
+			    xfrm_id_proto_match(x->id.proto, proto) &&
+			    x->props.alive) {
 				xfrm_state_hold(x);
 				spin_unlock_bh(&net->xfrm.xfrm_state_lock);