linux-kernel - [PATCH 4.19 15/53] net/sched: cls_u32: fix possible leak in u32_init

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Date:   Tue, 26 Apr 2022 10:20:55 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 15/53] net/sched: cls_u32: fix possible leak in u32_init_knode()

From: Eric Dumazet <edumazet@...gle.com>

[ Upstream commit ec5b0f605b105457f257f2870acad4a5d463984b ]

While investigating a related syzbot report,
I found that whenever call to tcf_exts_init()
from u32_init_knode() is failing, we end up
with an elevated refcount on ht->refcnt

To avoid that, only increase the refcount after
all possible errors have been evaluated.

Fixes: b9a24bb76bf6 ("net_sched: properly handle failure case of tcf_exts_init()")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
Cc: Jiri Pirko <jiri@...nulli.us>
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/sched/cls_u32.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index fe246e03fcd9..5eee26cf9011 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -873,10 +873,6 @@ static struct tc_u_knode *u32_init_knode(struct tcf_proto *tp,
 	new->flags = n->flags;
 	RCU_INIT_POINTER(new->ht_down, ht);
 
-	/* bump reference count as long as we hold pointer to structure */
-	if (ht)
-		ht->refcnt++;
-
 #ifdef CONFIG_CLS_U32_PERF
 	/* Statistics may be incremented by readers during update
 	 * so we must keep them in tact. When the node is later destroyed
@@ -899,6 +895,10 @@ static struct tc_u_knode *u32_init_knode(struct tcf_proto *tp,
 		return NULL;
 	}
 
+	/* bump reference count as long as we hold pointer to structure */
+	if (ht)
+		ht->refcnt++;
+
 	return new;
 }
 
-- 
2.35.1