[SRU][Focal/Jammy/Lunar][PATCH 2/3] net/sched: cls_fw: No longer copy tcf_result on update to avoid use-after-free

[Yuxuan Luo]

From: valis <sec at valis.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 at valis.email>
Reported-by: Bing-Jhong Billy Jheng <billy at starlabs.sg>
Signed-off-by: valis <sec at valis.email>
Signed-off-by: Jamal Hadi Salim <jhs at mojatatu.com>
Reviewed-by: Victor Nogueira <victor at mojatatu.com>
Reviewed-by: Pedro Tammela <pctammela at mojatatu.com>
Reviewed-by: M A Ramdhan <ramdhan at starlabs.sg>
Link: https://lore.kernel.org/r/20230729123202.72406-3-jhs@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(cherry picked from commit 76e42ae831991c828cffa8c37736ebfb831ad5ec)
CVE-2023-4128
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.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 8641f80593179..c49d6af0e0480 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