For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: [PATCH] HID: roccat: fix use-after-free and uninitialized-mutex races
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


roccat_disconnect() dropped devices_lock between reading device->exist
and later checking device->open to decide whether to free the device,
letting a concurrent roccat_release() free it first and turning the
later check into a use-after-free. Fix by keeping the whole lookup,
state update, and free-or-keep decision inside one devices_lock
critical section.

roccat_connect() also published the device via devices[minor] and
device_create() before initializing device->readers_lock and
device->cbuf_lock, letting a racing open() on the newly created node
take an uninitialized mutex. Fix by completing all initialization
before publishing the device.

Reported-by: syzbot+c492a9e154f81127551f@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c492a9e154f81127551f
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 drivers/hid/hid-roccat.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/drivers/hid/hid-roccat.c b/drivers/hid/hid-roccat.c
index 4f15eb951039..00499d6fa748 100644
--- a/drivers/hid/hid-roccat.c
+++ b/drivers/hid/hid-roccat.c
@@ -316,6 +316,14 @@ int roccat_connect(const struct class *klass, struct hid_device *hid, int report
 	if (!device)
 		return -ENOMEM;
 
+	init_waitqueue_head(&device->wait);
+	INIT_LIST_HEAD(&device->readers);
+	mutex_init(&device->readers_lock);
+	mutex_init(&device->cbuf_lock);
+	device->hid = hid;
+	device->exist = 1;
+	device->cbuf_end = 0;
+	device->report_size = report_size;
 	mutex_lock(&devices_lock);
 
 	for (minor = 0; minor < ROCCAT_MAX_DEVICES; ++minor) {
@@ -324,37 +332,30 @@ int roccat_connect(const struct class *klass, struct hid_device *hid, int report
 		break;
 	}
 
-	if (minor < ROCCAT_MAX_DEVICES) {
-		devices[minor] = device;
-	} else {
+	if (minor >= ROCCAT_MAX_DEVICES) {
 		mutex_unlock(&devices_lock);
 		kfree(device);
 		return -EINVAL;
 	}
 
+	device->minor = minor;
+
 	device->dev = device_create(klass, &hid->dev,
 			MKDEV(roccat_major, minor), NULL,
 			"%s%s%d", "roccat", hid->driver->name, minor);
 
 	if (IS_ERR(device->dev)) {
-		devices[minor] = NULL;
 		mutex_unlock(&devices_lock);
 		temp = PTR_ERR(device->dev);
 		kfree(device);
 		return temp;
 	}
 
-	mutex_unlock(&devices_lock);
+	/* Only publish once fully initialized, so roccat_open()/
+	* roccat_disconnect() never see a half-built device. */
+	devices[minor] = device;
 
-	init_waitqueue_head(&device->wait);
-	INIT_LIST_HEAD(&device->readers);
-	mutex_init(&device->readers_lock);
-	mutex_init(&device->cbuf_lock);
-	device->minor = minor;
-	device->hid = hid;
-	device->exist = 1;
-	device->cbuf_end = 0;
-	device->report_size = report_size;
+	mutex_unlock(&devices_lock);
 
 	return minor;
 }
@@ -369,15 +370,12 @@ void roccat_disconnect(int minor)
 
 	mutex_lock(&devices_lock);
 	device = devices[minor];
-	mutex_unlock(&devices_lock);
 
 	device->exist = 0; /* TODO exist maybe not needed */
 
 	device_destroy(device->dev->class, MKDEV(roccat_major, minor));
 
-	mutex_lock(&devices_lock);
 	devices[minor] = NULL;
-	mutex_unlock(&devices_lock);
 
 	if (device->open) {
 		hid_hw_close(device->hid);
@@ -385,6 +383,8 @@ void roccat_disconnect(int minor)
 	} else {
 		roccat_free_device(device);
 	}
+
+	mutex_unlock(&devices_lock);
 }
 EXPORT_SYMBOL_GPL(roccat_disconnect);
 
-- 
2.43.0