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: 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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c
index a32351da968cd7cb6fea11daf491af314093e07b..1212b057b129cbc5aa9f1b410dc5237741b8573d 100644 (file)
--- a/net/sched/cls_fw.c
+++ b/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 (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);
        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;
 
        } 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;
 }
 
        return 0;
 }