netdev - [PATCH net v2 2/3] net/sched: cls_fw: No longer copy tcf

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Message-Id: <20230729123202.72406-3-jhs@mojatatu.com>
Date: Sat, 29 Jul 2023 08:32:01 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: davem@...emloft.net,
	kuba@...nel.org,
	edumazet@...gle.com,
	pabeni@...hat.com
Cc: jiri@...nulli.us,
	xiyou.wangcong@...il.com,
	netdev@...r.kernel.org,
	sec@...is.email,
	ramdhan@...rlabs.sg,
	billy@...rlabs.sg,
	Jamal Hadi Salim <jhs@...atatu.com>
Subject: [PATCH net v2 2/3] net/sched: cls_fw: No longer copy tcf_result on update to avoid use-after-free

From: valis <sec@...is.email>

When fw_change() is called on an existing filter, the whole
tcf_result struct is always copied into the new instance of the filter.

This causes a problem when updating a filter bound to a class,
as tcf_unbind_filter() is always called on the old instance in the
success path, decreasing filter_cnt of the still referenced class
and allowing it to be deleted, leading to a use-after-free.

Fix this by no longer copying the tcf_result struct from the old filter.

Fixes: e35a8ee5993b ("net: sched: fw use RCU")
Reported-by: valis <sec@...is.email>
Reported-by: Bing-Jhong Billy Jheng <billy@...rlabs.sg>
Signed-off-by: valis <sec@...is.email>
Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>
---
 net/sched/cls_fw.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c
index 8641f8059317..c49d6af0e048 100644
--- a/net/sched/cls_fw.c
+++ b/net/sched/cls_fw.c
@@ -267,7 +267,6 @@ static int fw_change(struct net *net, struct sk_buff *in_skb,
 			return -ENOBUFS;
 
 		fnew->id = f->id;
-		fnew->res = f->res;
 		fnew->ifindex = f->ifindex;
 		fnew->tp = f->tp;
 
-- 
2.34.1