linux-kernel - [PATCH 3.16 10/61] net-sysfs: Call dev_hold always in rx_queue_add

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Message-ID: <lsq.1591725832.42968589@decadent.org.uk>
Date:   Tue, 09 Jun 2020 19:04:01 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Tetsuo Handa" <penguin-kernel@...ove.SAKURA.ne.jp>,
        "Lukas Bulwahn" <lukas.bulwahn@...il.com>,
        "David Miller" <davem@...emloft.net>,
        "Jouni Hogander" <jouni.hogander@...kie.com>,
        "syzbot" <syzbot+30209ea299c09d8785c9@...kaller.appspotmail.com>
Subject: [PATCH 3.16 10/61] net-sysfs: Call dev_hold always in
 rx_queue_add_kobject

3.16.85-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jouni Hogander <jouni.hogander@...kie.com>

commit ddd9b5e3e765d8ed5a35786a6cb00111713fe161 upstream.

Dev_hold has to be called always in rx_queue_add_kobject.
Otherwise usage count drops below 0 in case of failure in
kobject_init_and_add.

Fixes: b8eb718348b8 ("net-sysfs: Fix reference count leak in rx|netdev_queue_add_kobject")
Reported-by: syzbot <syzbot+30209ea299c09d8785c9@...kaller.appspotmail.com>
Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: David Miller <davem@...emloft.net>
Cc: Lukas Bulwahn <lukas.bulwahn@...il.com>
Signed-off-by: Jouni Hogander <jouni.hogander@...kie.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/core/net-sysfs.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -782,14 +782,17 @@ static int rx_queue_add_kobject(struct n
 	struct kobject *kobj = &queue->kobj;
 	int error = 0;
 
+	/* Kobject_put later will trigger rx_queue_release call which
+	 * decreases dev refcount: Take that reference here
+	 */
+	dev_hold(queue->dev);
+
 	kobj->kset = net->queues_kset;
 	error = kobject_init_and_add(kobj, &rx_queue_ktype, NULL,
 	    "rx-%u", index);
 	if (error)
 		goto err;
 
-	dev_hold(queue->dev);
-
 	if (net->sysfs_rx_queue_group) {
 		error = sysfs_create_group(kobj, net->sysfs_rx_queue_group);
 		if (error)