Re: possible deadlock in usb_deregister_dev

[Oliver Neukum <oneukum@suse.de>]

Am Montag, den 05.08.2019, 04:58 -0700 schrieb syzbot:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    e96407b4 usb-fuzzer: main usb gadget fuzzer driver
> git tree:       https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=13b5bc8a600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=792eb47789f57810
> dashboard link: https://syzkaller.appspot.com/bug?extid=a64a382964bf6c71a9c0
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+a64a382964bf6c71a9c0@syzkaller.appspotmail.com

#syz test: https://github.com/google/kasan.git e96407b4

From 973e82b3f583113e4d7fe5cd2f918a16022c4e38 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@suse.com>
Date: Tue, 6 Aug 2019 16:17:54 +0200
Subject: [PATCH] usb: iowarrior: fix deadlock on disconnect

We have to drop the mutex before we close() upon disconnect()
as close() needs the lock. This is safe to do by dropping the
mutex as intfdata is already set to NULL, so open() will fail.

Fixes: 03f36e885fc26 ("USB: open disconnect race in iowarrior")
Reported-by: syzbot+a64a382964bf6c71a9c0@syzkaller.appspotmail.com
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/misc/iowarrior.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c
index ba05dd80a020..f5bed9f29e56 100644
--- a/drivers/usb/misc/iowarrior.c
+++ b/drivers/usb/misc/iowarrior.c
@@ -866,19 +866,20 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 	dev = usb_get_intfdata(interface);
 	mutex_lock(&iowarrior_open_disc_lock);
 	usb_set_intfdata(interface, NULL);
+	/* prevent device read, write and ioctl */
+	dev->present = 0;
 
 	minor = dev->minor;
+	mutex_unlock(&iowarrior_open_disc_lock);
+	/* give back our minor - this will call close() locks need to be dropped at this point*/
 
-	/* give back our minor */
 	usb_deregister_dev(interface, &iowarrior_class);
 
 	mutex_lock(&dev->mutex);
 
 	/* prevent device read, write and ioctl */
-	dev->present = 0;
 
 	mutex_unlock(&dev->mutex);
-	mutex_unlock(&iowarrior_open_disc_lock);
 
 	if (dev->opened) {
 		/* There is a process that holds a filedescriptor to the device ,
-- 
2.16.4