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

[ Upstream commit 0323bce598eea038714f941ce2b22541c46d488f ]

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: 1da177e ("Linux-2.6.12-rc2")
Reported-by: M A Ramdhan <[email protected]>
Signed-off-by: M A Ramdhan <[email protected]>
Acked-by: Jamal Hadi Salim <[email protected]>
Reviewed-by: Pedro Tammela <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: M A Ramdhan

net/sched/cls_fw.c

@@ -210,11 +210,6 @@ 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);
@@ -231,6 +226,11 @@ 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;
 }