netdev - [PATCH net v2] net/sched: clear actions pointer in miss cookie init fail

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Date:   Sat, 15 Apr 2023 12:33:09 -0300
From:   Pedro Tammela <pctammela@...atatu.com>
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, marcelo.leitner@...il.com, paulb@...dia.com,
        simon.horman@...igine.com, Pedro Tammela <pctammela@...atatu.com>,
        Palash Oswal <oswalpalash@...il.com>
Subject: [PATCH net v2] net/sched: clear actions pointer in miss cookie init fail

Palash reports a UAF when using a modified version of syzkaller[1].

When 'tcf_exts_miss_cookie_base_alloc()' fails in 'tcf_exts_init_ex()'
a call to 'tcf_exts_destroy()' is made to free up the tcf_exts
resources.
In flower, a call to '__fl_put()' when 'tcf_exts_init_ex()' fails is made;
Then calling 'tcf_exts_destroy()', which triggers an UAF since the
already freed tcf_exts action pointer is lingering in the struct.

Before the offending patch, this was not an issue since there was no
case where the tcf_exts action pointer could linger. Therefore, restore
the old semantic by clearing the action pointer in case of a failure to
initialize the miss_cookie.

[1] https://github.com/cmu-pasta/linux-kernel-enriched-corpus

v1->v2: Fix compilation on configs without tc actions (kernel test robot)

Fixes: 80cd22c35c90 ("net/sched: cls_api: Support hardware miss to tc action")
Reported-by: Palash Oswal <oswalpalash@...il.com>
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
Signed-off-by: Pedro Tammela <pctammela@...atatu.com>
---
 net/sched/cls_api.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 2a6b6be0811b..35785a36c802 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -3235,6 +3235,9 @@ int tcf_exts_init_ex(struct tcf_exts *exts, struct net *net, int action,

 err_miss_alloc:
 	tcf_exts_destroy(exts);
+#ifdef CONFIG_NET_CLS_ACT
+	exts->actions = NULL;
+#endif
 	return err;
 }
 EXPORT_SYMBOL(tcf_exts_init_ex);
-- 
2.34.1