Commit 0323bce5 authored Jul 05, 2023 by M A Ramdhan Committed by Jakub Kicinski Jul 06, 2023

net/sched: cls_fw: Fix improper refcount update leads to use-after-free



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: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by: M A Ramdhan <ramdhan@starlabs.sg>
Signed-off-by: M A Ramdhan <ramdhan@starlabs.sg>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Pedro Tammela <pctammela@mojatatu.com>
Message-ID: <20230705161530.52003-1-ramdhan@starlabs.sg>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

parent 525c469e

net/sched/cls_fw.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -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;
		}