Commit 9a95fba9 authored May 25, 2023 by Uttkarsh Aggarwal Committed by Greg Kroah-Hartman Jun 09, 2023

usb: gadget: f_fs: Add unbind event before functionfs_unbind



commit efb6b535207395a5c7317993602e2503ca8cb4b3 upstream.

While exercising the unbind path, with the current implementation
the functionfs_unbind would be calling which waits for the ffs->mutex
to be available, however within the same time ffs_ep0_read is invoked
& if no setup packets are pending, it will invoke function
wait_event_interruptible_exclusive_locked_irq which by definition waits
for the ev.count to be increased inside the same mutex for which
functionfs_unbind is waiting.
This creates deadlock situation because the functionfs_unbind won't
get the lock until ev.count is increased which can only happen if
the caller ffs_func_unbind can proceed further.

Following is the illustration:

	CPU1				CPU2

ffs_func_unbind()		ffs_ep0_read()
				mutex_lock(ffs->mutex)
				wait_event(ffs->ev.count)
functionfs_unbind()
  mutex_lock(ffs->mutex)
  mutex_unlock(ffs->mutex)

ffs_event_add()

<deadlock>

Fix this by moving the event unbind before functionfs_unbind
to ensure the ev.count is incrased properly.

Fixes: 6a19da111057 ("usb: gadget: f_fs: Prevent race during ffs_ep0_queue_wait")
Cc: stable <stable@kernel.org>
Signed-off-by: Uttkarsh Aggarwal <quic_uaggarwa@quicinc.com>
Link: https://lore.kernel.org/r/20230525092854.7992-1-quic_uaggarwa@quicinc.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 5f99886c

drivers/usb/gadget/function/f_fs.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -3510,6 +3510,7 @@ static void ffs_func_unbind(struct usb_configuration *c,
		/* Drain any pending AIO completions */
		drain_workqueue(ffs->io_completion_wq);

		ffs_event_add(ffs, FUNCTIONFS_UNBIND);
		if (!--opts->refcnt)
		functionfs_unbind(ffs);

		@@ -3534,7 +3535,6 @@ static void ffs_func_unbind(struct usb_configuration *c,
		func->function.ssp_descriptors = NULL;
		func->interfaces_nums = NULL;

		ffs_event_add(ffs, FUNCTIONFS_UNBIND);
		}

		static struct usb_function ffs_alloc(struct usb_function_instance fi)