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

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Message-ID: <tencent_CFCFAA0DC325818D879200DDE3DD86193E07@qq.com>
Date: Wed, 27 Aug 2025 13:49:37 +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/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 78fcbb89cf32..137b5b660683 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -929,10 +929,10 @@ int xfrm_state_flush(struct net *net, u8 proto, bool task_valid)
 	err = -ESRCH;
 	for (i = 0; i <= net->xfrm.state_hmask; i++) {
 		struct xfrm_state *x;
-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->km.state != XFRM_STATE_DEAD) {
 				xfrm_state_hold(x);
 				spin_unlock_bh(&net->xfrm.xfrm_state_lock);
 
@@ -940,11 +940,9 @@ int xfrm_state_flush(struct net *net, u8 proto, bool task_valid)
 				xfrm_audit_state_delete(x, err ? 0 : 1,
 							task_valid);
 				xfrm_state_put(x);
-				if (!err)
-					cnt++;
+				cnt++;
 
 				spin_lock_bh(&net->xfrm.xfrm_state_lock);
-				goto restart;
 			}
 		}
 	}
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 78fcbb89cf32..3de1ac70019f 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -929,10 +929,10 @@ int xfrm_state_flush(struct net *net, u8 proto, bool task_valid)
 	err = -ESRCH;
 	for (i = 0; i <= net->xfrm.state_hmask; i++) {
 		struct xfrm_state *x;
-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->km.state != XFRM_STATE_DEAD) {
 				xfrm_state_hold(x);
 				spin_unlock_bh(&net->xfrm.xfrm_state_lock);
 
@@ -940,11 +940,9 @@ int xfrm_state_flush(struct net *net, u8 proto, bool task_valid)
 				xfrm_audit_state_delete(x, err ? 0 : 1,
 							task_valid);
 				xfrm_state_put(x);
-				if (!err)
-					cnt++;
+				cnt++;
 
 				spin_lock_bh(&net->xfrm.xfrm_state_lock);
-				goto restart;
 			}
 		}
 	}
@@ -1557,6 +1555,7 @@ xfrm_state_find(const xfrm_address_t *daddr, const xfrm_address_t *saddr,
 #endif
 		if (km_query(x, tmpl, pol) == 0) {
 			spin_lock_bh(&net->xfrm.xfrm_state_lock);
+			BUG_ON(x->km.state == XFRM_STATE_DEAD);
 			x->km.state = XFRM_STATE_ACQ;
 			x->dir = XFRM_SA_DIR_OUT;
 			list_add(&x->km.all, &net->xfrm.state_all);
@@ -1722,6 +1721,7 @@ static void __xfrm_state_insert(struct xfrm_state *x)
 	struct net *net = xs_net(x);
 	unsigned int h;
 
+	BUG_ON(x->km.state == XFRM_STATE_DEAD);
 	list_add(&x->km.all, &net->xfrm.state_all);
 
 	/* Sanitize mark before store */