USB: Gadget: core: Help prevent panic during UVC unconfigure

In the Linux kernel, the following vulnerability has been resolved: USB: Gadget: core: Help prevent panic during UVC unconfigure Avichal Rakesh reported a kernel panic that occurred when the UVC gadget driver was removed from a gadget's configuration. The panic involves a somewhat complicated interaction between the kernel driver and a userspace component (as described in the Link tag below), but the analysis did make one thing clear: The Gadget core should accomodate gadget drivers calling usb_gadget_deactivate() as part of their unbind procedure. Currently this doesn't work. gadget_unbind_driver() calls driver->unbind() while holding the udc->connect_lock mutex, and usb_gadget_deactivate() attempts to acquire that mutex, which will result in a deadlock. The simple fix is for gadget_unbind_driver() to release the mutex when invoking the ->unbind() callback. There is no particular reason for it to be holding the mutex at that time, and the mutex isn't held while the ->bind() callback is invoked. So we'll drop the mutex before performing the unbind callback and reacquire it afterward. We'll also add a couple of comments to usb_gadget_activate() and usb_gadget_deactivate(). Because they run in process context they must not be called from a gadget driver's ->disconnect() callback, which (according to the kerneldoc for struct usb_gadget_driver in include/linux/usb/gadget.h) may run in interrupt context. This may help prevent similar bugs from arising in the future.

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Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于gadget_unbind_driver在调用unbind回调时持有互斥锁，可能导致死锁。

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