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: [e-mail]
Closes: https://syzkaller.appspot.com/bug?extid=0c85cae3350b7d486aee
Tested-by: [e-mail]
Fixes: 22a5dc0e5e3e ("net: sched: Introduce connmark action")
Signed-off-by: Ranganath V N <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Acked-by: Cong Wang <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

net/sched/act_connmark.c

···
 	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);