netdev - [PATCH net 1/3] net/sched: cls_u32: No longer copy tcf

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Date: Fri, 21 Jul 2023 17:48:54 +0000
From: valis <sec@...is.email>
To: netdev@...r.kernel.org
Cc: jhs@...atatu.com,
	xiyou.wangcong@...il.com,
	jiri@...nulli.us,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	pctammela@...atatu.com,
	victor@...atatu.com,
	ramdhan@...rlabs.sg,
	billy@...rlabs.sg
Subject: [PATCH net 1/3] net/sched: cls_u32: No longer copy tcf_result on update to avoid use-after-free

When u32_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: de5df63228fc ("net: sched: cls_u32 changes to knode must appear atomic to readers")
Reported-by: valis <sec@...is.email>
Reported-by: M A Ramdhan <ramdhan@...rlabs.sg>
Signed-off-by: valis <sec@...is.email>
Cc: stable@...r.kernel.org
---
 net/sched/cls_u32.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 5abf31e432ca..19aa60d1eea7 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -826,7 +826,6 @@ static struct tc_u_knode *u32_init_knode(struct net *net, struct tcf_proto *tp,
 
 	new->ifindex = n->ifindex;
 	new->fshift = n->fshift;
-	new->res = n->res;
 	new->flags = n->flags;
 	RCU_INIT_POINTER(new->ht_down, ht);
 
-- 
2.30.2