[SRU Focal/Jammy/OEM-5.17/Kinetic/OEM-6.0/Lunar] net/sched: cls_fw: Fix improper refcount update leads to use-after-free

Cengiz Can cengiz.can at canonical.com
Fri Jul 28 06:57:39 UTC 2023


From: M A Ramdhan <ramdhan at starlabs.sg>

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 at starlabs.sg>
Signed-off-by: M A Ramdhan <ramdhan at starlabs.sg>
Acked-by: Jamal Hadi Salim <jhs at mojatatu.com>
Reviewed-by: Pedro Tammela <pctammela at mojatatu.com>
Message-ID: <20230705161530.52003-1-ramdhan at starlabs.sg>
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
CVE-2023-3776
(cherry picked from commit 0323bce598eea038714f941ce2b22541c46d488f)
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 net/sched/cls_fw.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c
index ae9439a6c56c..8641f8059317 100644
--- 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;
 }
 
-- 
2.39.2




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