From: Alan Stern stern@rowland.harvard.edu
commit 1016fc0c096c92dd0e6e0541daac7a7868169903 upstream.
A recent commit expanding the scope of the udc_lock mutex in the gadget core managed to cause an obscure and slightly bizarre lockdep violation. In abbreviated form:
====================================================== WARNING: possible circular locking dependency detected 5.19.0-rc7+ #12510 Not tainted ------------------------------------------------------ udevadm/312 is trying to acquire lock: ffff80000aae1058 (udc_lock){+.+.}-{3:3}, at: usb_udc_uevent+0x54/0xe0
but task is already holding lock: ffff000002277548 (kn->active#4){++++}-{0:0}, at: kernfs_seq_start+0x34/0xe0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (kn->active#4){++++}-{0:0}: lock_acquire+0x68/0x84 __kernfs_remove+0x268/0x380 kernfs_remove_by_name_ns+0x58/0xac sysfs_remove_file_ns+0x18/0x24 device_del+0x15c/0x440
-> #2 (device_links_lock){+.+.}-{3:3}: lock_acquire+0x68/0x84 __mutex_lock+0x9c/0x430 mutex_lock_nested+0x38/0x64 device_link_remove+0x3c/0xa0 _regulator_put.part.0+0x168/0x190 regulator_put+0x3c/0x54 devm_regulator_release+0x14/0x20
-> #1 (regulator_list_mutex){+.+.}-{3:3}: lock_acquire+0x68/0x84 __mutex_lock+0x9c/0x430 mutex_lock_nested+0x38/0x64 regulator_lock_dependent+0x54/0x284 regulator_enable+0x34/0x80 phy_power_on+0x24/0x130 __dwc2_lowlevel_hw_enable+0x100/0x130 dwc2_lowlevel_hw_enable+0x18/0x40 dwc2_hsotg_udc_start+0x6c/0x2f0 gadget_bind_driver+0x124/0x1f4
-> #0 (udc_lock){+.+.}-{3:3}: __lock_acquire+0x1298/0x20cc lock_acquire.part.0+0xe0/0x230 lock_acquire+0x68/0x84 __mutex_lock+0x9c/0x430 mutex_lock_nested+0x38/0x64 usb_udc_uevent+0x54/0xe0
Evidently this was caused by the scope of udc_mutex being too large. The mutex is only meant to protect udc->driver along with a few other things. As far as I can tell, there's no reason for the mutex to be held while the gadget core calls a gadget driver's ->bind or ->unbind routine, or while a UDC is being started or stopped. (This accounts for link #1 in the chain above, where the mutex is held while the dwc2_hsotg_udc is started as part of driver probing.)
Gadget drivers' ->disconnect callbacks are problematic. Even though usb_gadget_disconnect() will now acquire the udc_mutex, there's a window in usb_gadget_bind_driver() between the times when the mutex is released and the ->bind callback is invoked. If a disconnect occurred during that window, we could call the driver's ->disconnect routine before its ->bind routine. To prevent this from happening, it will be necessary to prevent a UDC from connecting while it has no gadget driver. This should be done already but it doesn't seem to be; currently usb_gadget_connect() has no check for this. Such a check will have to be added later.
Some degree of mutual exclusion is required in soft_connect_store(), which can dereference udc->driver at arbitrary times since it is a sysfs callback. The solution here is to acquire the gadget's device lock rather than the udc_mutex. Since the driver core guarantees that the device lock is always held during driver binding and unbinding, this will make the accesses in soft_connect_store() mutually exclusive with any changes to udc->driver.
Lastly, it turns out there is one place which should hold the udc_mutex but currently does not: The function_show() routine needs protection while it dereferences udc->driver. The missing lock and unlock calls are added.
Link: https://lore.kernel.org/all/b2ba4245-9917-e399-94c8-03a383e7070e@samsung.com... Fixes: 2191c00855b0 ("USB: gadget: Fix use-after-free Read in usb_udc_uevent()") Cc: Felipe Balbi balbi@kernel.org Cc: stable@vger.kernel.org Reported-by: Marek Szyprowski m.szyprowski@samsung.com Tested-by: Marek Szyprowski m.szyprowski@samsung.com Signed-off-by: Alan Stern stern@rowland.harvard.edu Link: https://lore.kernel.org/r/YwkfhdxA/I2nOcK7@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/gadget/udc/core.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-)
--- a/drivers/usb/gadget/udc/core.c +++ b/drivers/usb/gadget/udc/core.c @@ -736,7 +736,10 @@ int usb_gadget_disconnect(struct usb_gad ret = gadget->ops->pullup(gadget, 0); if (!ret) { gadget->connected = 0; - gadget->udc->driver->disconnect(gadget); + mutex_lock(&udc_lock); + if (gadget->udc->driver) + gadget->udc->driver->disconnect(gadget); + mutex_unlock(&udc_lock); }
out: @@ -1489,7 +1492,6 @@ static int gadget_bind_driver(struct dev
usb_gadget_udc_set_speed(udc, driver->max_speed);
- mutex_lock(&udc_lock); ret = driver->bind(udc->gadget, driver); if (ret) goto err_bind; @@ -1499,7 +1501,6 @@ static int gadget_bind_driver(struct dev goto err_start; usb_gadget_enable_async_callbacks(udc); usb_udc_connect_control(udc); - mutex_unlock(&udc_lock);
kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE); return 0; @@ -1512,6 +1513,7 @@ static int gadget_bind_driver(struct dev dev_err(&udc->dev, "failed to start %s: %d\n", driver->function, ret);
+ mutex_lock(&udc_lock); udc->driver = NULL; driver->is_bound = false; mutex_unlock(&udc_lock); @@ -1529,7 +1531,6 @@ static void gadget_unbind_driver(struct
kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE);
- mutex_lock(&udc_lock); usb_gadget_disconnect(gadget); usb_gadget_disable_async_callbacks(udc); if (gadget->irq) @@ -1537,6 +1538,7 @@ static void gadget_unbind_driver(struct udc->driver->unbind(gadget); usb_gadget_udc_stop(udc);
+ mutex_lock(&udc_lock); driver->is_bound = false; udc->driver = NULL; mutex_unlock(&udc_lock); @@ -1612,7 +1614,7 @@ static ssize_t soft_connect_store(struct struct usb_udc *udc = container_of(dev, struct usb_udc, dev); ssize_t ret;
- mutex_lock(&udc_lock); + device_lock(&udc->gadget->dev); if (!udc->driver) { dev_err(dev, "soft-connect without a gadget driver\n"); ret = -EOPNOTSUPP; @@ -1633,7 +1635,7 @@ static ssize_t soft_connect_store(struct
ret = n; out: - mutex_unlock(&udc_lock); + device_unlock(&udc->gadget->dev); return ret; } static DEVICE_ATTR_WO(soft_connect); @@ -1652,11 +1654,15 @@ static ssize_t function_show(struct devi char *buf) { struct usb_udc *udc = container_of(dev, struct usb_udc, dev); - struct usb_gadget_driver *drv = udc->driver; + struct usb_gadget_driver *drv; + int rc = 0;
- if (!drv || !drv->function) - return 0; - return scnprintf(buf, PAGE_SIZE, "%s\n", drv->function); + mutex_lock(&udc_lock); + drv = udc->driver; + if (drv && drv->function) + rc = scnprintf(buf, PAGE_SIZE, "%s\n", drv->function); + mutex_unlock(&udc_lock); + return rc; } static DEVICE_ATTR_RO(function);