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: 1da177e4c3f4 ("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>

diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c
index ae9439a6c56c90f8f1711c8cde33cd967f1ef7e5..8641f805931793a468abb01b7fcd95c8cf9891f4 100644 (file)
--- a/net/sched/cls_fw.c
+++ b/net/sched/cls_fw.c
@@ -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;
 }