linux-kernel - [PATCH net v4 1/2] net: sched: act_connmark: initialize struct tc

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Message-ID: <20251109091336.9277-2-vnranganath.20@gmail.com>
Date: Sun,  9 Nov 2025 14:43:35 +0530
From: Ranganath V N <vnranganath.20@...il.com>
To: edumazet@...gle.com,
	davem@...emloft.net,
	david.hunter.linux@...il.com,
	horms@...nel.org,
	jhs@...atatu.com,
	jiri@...nulli.us,
	khalid@...nel.org,
	kuba@...nel.org,
	pabeni@...hat.com,
	vnranganath.20@...il.com,
	xiyou.wangcong@...il.com
Cc: linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	skhan@...uxfoundation.org,
	syzbot+0c85cae3350b7d486aee@...kaller.appspotmail.com
Subject: [PATCH net v4 1/2] net: sched: act_connmark: initialize struct tc_ife to fix kernel leak

In tcf_connmark_dump(), the variable 'opt' was partially initialized using a
designatied initializer. While the padding bytes are reamined
uninitialized. nla_put() copies the entire structure into a
netlink message, these uninitialized bytes leaked to userspace.

Initialize the structure with memset before assigning its fields
to ensure all members and padding are cleared prior to beign copied.

Reported-by: syzbot+0c85cae3350b7d486aee@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=0c85cae3350b7d486aee
Tested-by: syzbot+0c85cae3350b7d486aee@...kaller.appspotmail.com
Fixes: 22a5dc0e5e3e ("net: sched: Introduce connmark action")
Signed-off-by: Ranganath V N <vnranganath.20@...il.com>
---
 net/sched/act_connmark.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/sched/act_connmark.c b/net/sched/act_connmark.c
index 3e89927d7116..26ba8c2d20ab 100644
--- a/net/sched/act_connmark.c
+++ b/net/sched/act_connmark.c
@@ -195,13 +195,15 @@ static inline int tcf_connmark_dump(struct sk_buff *skb, struct tc_action *a,
 	const struct tcf_connmark_info *ci = to_connmark(a);
 	unsigned char *b = skb_tail_pointer(skb);
 	const struct tcf_connmark_parms *parms;
-	struct tc_connmark opt = {
-		.index   = ci->tcf_index,
-		.refcnt  = refcount_read(&ci->tcf_refcnt) - ref,
-		.bindcnt = atomic_read(&ci->tcf_bindcnt) - bind,
-	};
+	struct tc_connmark opt;
 	struct tcf_t t;
 
+	memset(&opt, 0, sizeof(opt));
+
+	opt.index   = ci->tcf_index;
+	opt.refcnt  = refcount_read(&ci->tcf_refcnt) - ref;
+	opt.bindcnt = atomic_read(&ci->tcf_bindcnt) - bind;
+
 	rcu_read_lock();
 	parms = rcu_dereference(ci->parms);
 
-- 
2.43.0