linux-kernel - [PATCH 2/2] media: dvb-usb: Fix use-after-free access

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Date:   Wed, 20 Jan 2021 11:20:57 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stefan Seyfried <seife+kernel@...systems.com>
Subject: [PATCH 2/2] media: dvb-usb: Fix use-after-free access

dvb_usb_device_init() copies the properties to the own data, so that
the callers can release the original properties later (as done in the
commit 299c7007e936 "media: dw2102: Fix memleak on sequence of
probes").  However, it also stores dev->desc pointer that is a
reference to the original properties data.  Since dev->desc is
referred later, it may result in use-after-free, in the worst case,
leading to a kernel Oops as reported.

This patch addresses the problem by allocating and copying the
properties at first, then get the desc from the copied properties.

Reported-and-tested-by: Stefan Seyfried <seife+kernel@...systems.com>
BugLink: http://bugzilla.opensuse.org/show_bug.cgi?id=1181104
Cc: <stable@...r.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
---
 drivers/media/usb/dvb-usb/dvb-usb-init.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c
index 5befec87f26a..07ff9b4d2f34 100644
--- a/drivers/media/usb/dvb-usb/dvb-usb-init.c
+++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c
@@ -255,27 +255,30 @@ int dvb_usb_device_init(struct usb_interface *intf,
 	if (du != NULL)
 		*du = NULL;
 
-	if ((desc = dvb_usb_find_device(udev, props, &cold)) == NULL) {
+	d = kzalloc(sizeof(struct dvb_usb_device), GFP_KERNEL);
+	if (!d) {
+		err("no memory for 'struct dvb_usb_device'");
+		return -ENOMEM;
+	}
+
+	memcpy(&d->props, props, sizeof(struct dvb_usb_device_properties));
+
+	desc = dvb_usb_find_device(udev, &d->props, &cold);
+	if (!desc) {
 		deb_err("something went very wrong, device was not found in current device list - let's see what comes next.\n");
-		return -ENODEV;
+		ret = -ENODEV;
+		goto error;
 	}
 
 	if (cold) {
 		info("found a '%s' in cold state, will try to load a firmware", desc->name);
 		ret = dvb_usb_download_firmware(udev, props);
 		if (!props->no_reconnect || ret != 0)
-			return ret;
+			goto error;
 	}
 
 	info("found a '%s' in warm state.", desc->name);
-	d = kzalloc(sizeof(struct dvb_usb_device), GFP_KERNEL);
-	if (d == NULL) {
-		err("no memory for 'struct dvb_usb_device'");
-		return -ENOMEM;
-	}
-
 	d->udev = udev;
-	memcpy(&d->props, props, sizeof(struct dvb_usb_device_properties));
 	d->desc = desc;
 	d->owner = owner;
 
-- 
2.26.2