netdev - [PATCH v2 net] net: hso: check for allocation failure in hso_create_bulk_serial

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Message-ID: <YJ6IMH7jI9QFdGIX@mwanda>
Date:   Fri, 14 May 2021 17:24:48 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Johan Hovold <johan@...nel.org>
Cc:     Jakub Kicinski <kuba@...nel.org>, Oliver Neukum <oneukum@...e.com>,
        Anirudh Rayabharam <mail@...rudhrb.com>,
        Johan Hovold <johan@...nel.org>,
        Zheng Yongjun <zhengyongjun3@...wei.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Rustam Kovhaev <rkovhaev@...il.com>, linux-usb@...r.kernel.org,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH v2 net] net: hso: check for allocation failure in
 hso_create_bulk_serial_device()

In current kernels, small allocations never actually fail so this
patch shouldn't affect runtime.

Originally this error handling code written with the idea that if
the "serial->tiocmget" allocation failed, then we would continue
operating instead of bailing out early.  But in later years we added
an unchecked dereference on the next line.

	serial->tiocmget->serial_state_notification = kzalloc();
        ^^^^^^^^^^^^^^^^^^

Since these allocations are never going fail in real life, this is
mostly a philosophical debate, but I think bailing out early is the
correct behavior that the user would want.  And generally it's safer to
bail as soon an error happens.

Fixes: af0de1303c4e ("usb: hso: obey DMA rules in tiocmget")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
v2: Do more extensive clean up.  As Johan pointed out the comments and
later NULL checks can be removed.

 drivers/net/usb/hso.c | 37 ++++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c
index 3ef4b2841402..260f850d69eb 100644
--- a/drivers/net/usb/hso.c
+++ b/drivers/net/usb/hso.c
@@ -2618,29 +2618,28 @@ static struct hso_device *hso_create_bulk_serial_device(
 		num_urbs = 2;
 		serial->tiocmget = kzalloc(sizeof(struct hso_tiocmget),
 					   GFP_KERNEL);
+		if (!serial->tiocmget)
+			goto exit;
 		serial->tiocmget->serial_state_notification
 			= kzalloc(sizeof(struct hso_serial_state_notification),
 					   GFP_KERNEL);
-		/* it isn't going to break our heart if serial->tiocmget
-		 *  allocation fails don't bother checking this.
-		 */
-		if (serial->tiocmget && serial->tiocmget->serial_state_notification) {
-			tiocmget = serial->tiocmget;
-			tiocmget->endp = hso_get_ep(interface,
-						    USB_ENDPOINT_XFER_INT,
-						    USB_DIR_IN);
-			if (!tiocmget->endp) {
-				dev_err(&interface->dev, "Failed to find INT IN ep\n");
-				goto exit;
-			}
-
-			tiocmget->urb = usb_alloc_urb(0, GFP_KERNEL);
-			if (tiocmget->urb) {
-				mutex_init(&tiocmget->mutex);
-				init_waitqueue_head(&tiocmget->waitq);
-			} else
-				hso_free_tiomget(serial);
+		if (!serial->tiocmget->serial_state_notification)
+			goto exit;
+		tiocmget = serial->tiocmget;
+		tiocmget->endp = hso_get_ep(interface,
+					    USB_ENDPOINT_XFER_INT,
+					    USB_DIR_IN);
+		if (!tiocmget->endp) {
+			dev_err(&interface->dev, "Failed to find INT IN ep\n");
+			goto exit;
 		}
+
+		tiocmget->urb = usb_alloc_urb(0, GFP_KERNEL);
+		if (tiocmget->urb) {
+			mutex_init(&tiocmget->mutex);
+			init_waitqueue_head(&tiocmget->waitq);
+		} else
+			hso_free_tiomget(serial);
 	}
 	else
 		num_urbs = 1;
-- 
2.30.2