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Date: Tue, 17 Sep 2019 14:24:04 +0200
From: Johan Hovold <johan@...nel.org>
To: syzbot <syzbot+f9549f5ee8a5416f0b95@...kaller.appspotmail.com>
Cc: andreyknvl@...gle.com, gregkh@...uxfoundation.org,
linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
stern@...land.harvard.edu, syzkaller-bugs@...glegroups.com,
Oliver Neukum <oneukum@...e.com>
Subject: Re: possible deadlock in usb_deregister_dev (2)
On Mon, Sep 16, 2019 at 02:42:06PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
>
> HEAD commit: f0df5c1b 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=175cdb95600000
> kernel config: https://syzkaller.appspot.com/x/.config?x=5c6633fa4ed00be5
> dashboard link: https://syzkaller.appspot.com/bug?extid=f9549f5ee8a5416f0b95
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13961369600000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=139c811d600000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+f9549f5ee8a5416f0b95@...kaller.appspotmail.com
>
> usb 1-1: config 0 descriptor??
> legousbtower 1-1:0.219: LEGO USB Tower firmware version is 129.136 build
> 65535
> legousbtower 1-1:0.219: LEGO USB Tower #-160 now attached to major 180
> minor 0
> usb 1-1: USB disconnect, device number 2
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.3.0-rc7+ #0 Not tainted
> ------------------------------------------------------
> kworker/0:1/12 is trying to acquire lock:
> 0000000098630ee4 (minor_rwsem){++++}, at: usb_deregister_dev+0x95/0x230
> drivers/usb/core/file.c:239
>
> but task is already holding lock:
> 00000000d9ad5b6f (open_disc_mutex){+.+.}, at: tower_disconnect+0x45/0x300
> drivers/usb/misc/legousbtower.c:945
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (open_disc_mutex){+.+.}:
> __mutex_lock_common kernel/locking/mutex.c:930 [inline]
> __mutex_lock+0x158/0x1360 kernel/locking/mutex.c:1077
> tower_open+0xce/0x9b0 drivers/usb/misc/legousbtower.c:335
> usb_open+0x1df/0x270 drivers/usb/core/file.c:48
> chrdev_open+0x219/0x5c0 fs/char_dev.c:414
> do_dentry_open+0x494/0x1120 fs/open.c:797
> do_last fs/namei.c:3416 [inline]
> path_openat+0x1430/0x3f50 fs/namei.c:3533
> do_filp_open+0x1a1/0x280 fs/namei.c:3563
> do_sys_open+0x3c0/0x580 fs/open.c:1089
> do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:296
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> -> #0 (minor_rwsem){++++}:
> check_prev_add kernel/locking/lockdep.c:2405 [inline]
> check_prevs_add kernel/locking/lockdep.c:2507 [inline]
> validate_chain kernel/locking/lockdep.c:2897 [inline]
> __lock_acquire+0x1f7c/0x3b50 kernel/locking/lockdep.c:3880
> lock_acquire+0x127/0x320 kernel/locking/lockdep.c:4412
> down_write+0x92/0x150 kernel/locking/rwsem.c:1500
> usb_deregister_dev+0x95/0x230 drivers/usb/core/file.c:239
> tower_disconnect+0xa8/0x300 drivers/usb/misc/legousbtower.c:951
> usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:423
> __device_release_driver drivers/base/dd.c:1134 [inline]
> device_release_driver_internal+0x42f/0x500 drivers/base/dd.c:1165
> bus_remove_device+0x2dc/0x4a0 drivers/base/bus.c:556
> device_del+0x420/0xb10 drivers/base/core.c:2339
> usb_disable_device+0x211/0x690 drivers/usb/core/message.c:1237
> usb_disconnect+0x284/0x8d0 drivers/usb/core/hub.c:2199
> hub_port_connect drivers/usb/core/hub.c:4949 [inline]
> hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
> port_event drivers/usb/core/hub.c:5359 [inline]
> hub_event+0x1454/0x3640 drivers/usb/core/hub.c:5441
> process_one_work+0x92b/0x1530 kernel/workqueue.c:2269
> worker_thread+0x96/0xe20 kernel/workqueue.c:2415
> kthread+0x318/0x420 kernel/kthread.c:255
> ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(open_disc_mutex);
> lock(minor_rwsem);
> lock(open_disc_mutex);
> lock(minor_rwsem);
>
> *** DEADLOCK ***
This should be fixed by the below patch. Looks like we may have a
similar issue in a few more drivers. Fixing them up next.
Johan
#syz test: https://github.com/google/kasan.git f0df5c1b
>From c2c2800f2687be963acc222045c8fd89f3877642 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@...nel.org>
Date: Tue, 17 Sep 2019 12:32:22 +0200
Subject: [PATCH] USB: legousbtower: fix deadlock on disconnect
Fix a potential deadlock if disconnect races with open.
Since commit d4ead16f50f9 ("USB: prevent char device open/deregister
race") core holds an rw-semaphore while open is called and when
releasing the minor number during deregistration. This can lead to an
ABBA deadlock if a driver takes a lock in open which it also holds
during deregistration.
This effectively reverts commit 78663ecc344b ("USB: disconnect open race
in legousbtower") which needlessly introduced this issue after a generic
fix for this race had been added to core by commit d4ead16f50f9 ("USB:
prevent char device open/deregister race").
Fixes: 78663ecc344b ("USB: disconnect open race in legousbtower")
Cc: stable <stable@...r.kernel.org> # 2.6.24
Cc: Alan Stern <stern@...land.harvard.edu>
Cc: Oliver Neukum <oneukum@...e.com>
Reported-by: syzbot+f9549f5ee8a5416f0b95@...kaller.appspotmail.com
Signed-off-by: Johan Hovold <johan@...nel.org>
---
drivers/usb/misc/legousbtower.c | 19 ++-----------------
1 file changed, 2 insertions(+), 17 deletions(-)
diff --git a/drivers/usb/misc/legousbtower.c b/drivers/usb/misc/legousbtower.c
index 006cf13b2199..c125f03436a1 100644
--- a/drivers/usb/misc/legousbtower.c
+++ b/drivers/usb/misc/legousbtower.c
@@ -179,7 +179,6 @@ static const struct usb_device_id tower_table[] = {
};
MODULE_DEVICE_TABLE (usb, tower_table);
-static DEFINE_MUTEX(open_disc_mutex);
#define LEGO_USB_TOWER_MINOR_BASE 160
@@ -332,18 +331,14 @@ static int tower_open (struct inode *inode, struct file *file)
goto exit;
}
- mutex_lock(&open_disc_mutex);
dev = usb_get_intfdata(interface);
-
if (!dev) {
- mutex_unlock(&open_disc_mutex);
retval = -ENODEV;
goto exit;
}
/* lock this device */
if (mutex_lock_interruptible(&dev->lock)) {
- mutex_unlock(&open_disc_mutex);
retval = -ERESTARTSYS;
goto exit;
}
@@ -351,12 +346,10 @@ static int tower_open (struct inode *inode, struct file *file)
/* allow opening only once */
if (dev->open_count) {
- mutex_unlock(&open_disc_mutex);
retval = -EBUSY;
goto unlock_exit;
}
dev->open_count = 1;
- mutex_unlock(&open_disc_mutex);
/* reset the tower */
result = usb_control_msg (dev->udev,
@@ -423,10 +416,9 @@ static int tower_release (struct inode *inode, struct file *file)
if (dev == NULL) {
retval = -ENODEV;
- goto exit_nolock;
+ goto exit;
}
- mutex_lock(&open_disc_mutex);
if (mutex_lock_interruptible(&dev->lock)) {
retval = -ERESTARTSYS;
goto exit;
@@ -456,10 +448,7 @@ static int tower_release (struct inode *inode, struct file *file)
unlock_exit:
mutex_unlock(&dev->lock);
-
exit:
- mutex_unlock(&open_disc_mutex);
-exit_nolock:
return retval;
}
@@ -910,7 +899,6 @@ static int tower_probe (struct usb_interface *interface, const struct usb_device
if (retval) {
/* something prevented us from registering this driver */
dev_err(idev, "Not able to get a minor for this device.\n");
- usb_set_intfdata (interface, NULL);
goto error;
}
dev->minor = interface->minor;
@@ -942,16 +930,13 @@ static void tower_disconnect (struct usb_interface *interface)
int minor;
dev = usb_get_intfdata (interface);
- mutex_lock(&open_disc_mutex);
- usb_set_intfdata (interface, NULL);
minor = dev->minor;
- /* give back our minor */
+ /* give back our minor and prevent further open() */
usb_deregister_dev (interface, &tower_class);
mutex_lock(&dev->lock);
- mutex_unlock(&open_disc_mutex);
/* if the device is not opened, then we clean up right now */
if (!dev->open_count) {
--
2.23.0
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