netdev - [PATCH net] net/sched: cls_fw: Fix improper refcount update leads to use-after-free

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Message-Id: <20230705161530.52003-1-ramdhan@starlabs.sg>
Date: Wed,  5 Jul 2023 12:15:30 -0400
From: jhs@...atatu.com
To: davem@...emloft.net,
	kuba@...nel.org,
	edumazet@...gle.com,
	pabeni@...hat.com
Cc: xiyou.wangcong@...il.com,
	jiri@...nulli.us,
	netdev@...r.kernel.org,
	ramdhan@...rlabs.sg,
	Jamal Hadi Salim <jhs@...atatu.com>
Subject: [PATCH net] net/sched: cls_fw: Fix improper refcount update leads to  use-after-free

From: M A Ramdhan <ramdhan@...rlabs.sg>

In the event of a failure in tcf_change_indev(), fw_set_parms() will
immediately return an error after incrementing or decrementing
reference counter in tcf_bind_filter().  If attacker can control
reference counter to zero and make reference freed, leading to
use after free.

In order to prevent this, move the point of possible failure above the
point where the TC_FW_CLASSID is handled.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: M A Ramdhan <ramdhan@...rlabs.sg>
Signed-off-by: M A Ramdhan <ramdhan@...rlabs.sg>
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
---
 net/sched/cls_fw.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c
index ae9439a6c56c..8641f8059317 100644
--- a/net/sched/cls_fw.c
+++ b/net/sched/cls_fw.c
@@ -212,11 +212,6 @@ static int fw_set_parms(struct net *net, struct tcf_proto *tp,
 	if (err < 0)
 		return err;
 
-	if (tb[TCA_FW_CLASSID]) {
-		f->res.classid = nla_get_u32(tb[TCA_FW_CLASSID]);
-		tcf_bind_filter(tp, &f->res, base);
-	}
-
 	if (tb[TCA_FW_INDEV]) {
 		int ret;
 		ret = tcf_change_indev(net, tb[TCA_FW_INDEV], extack);
@@ -233,6 +228,11 @@ static int fw_set_parms(struct net *net, struct tcf_proto *tp,
 	} else if (head->mask != 0xFFFFFFFF)
 		return err;
 
+	if (tb[TCA_FW_CLASSID]) {
+		f->res.classid = nla_get_u32(tb[TCA_FW_CLASSID]);
+		tcf_bind_filter(tp, &f->res, base);
+	}
+
 	return 0;
 }
 
-- 
2.34.1