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Commit a8d40942 authored by Udipto Goswami's avatar Udipto Goswami Committed by Greg Kroah-Hartman
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usb: gadget: f_fs: Prevent race during ffs_ep0_queue_wait 



[ Upstream commit 6a19da111057f69214b97c62fb0ac59023970850 ]

While performing fast composition switch, there is a possibility that the
process of ffs_ep0_write/ffs_ep0_read get into a race condition
due to ep0req being freed up from functionfs_unbind.

Consider the scenario that the ffs_ep0_write calls the ffs_ep0_queue_wait
by taking a lock &ffs->ev.waitq.lock. However, the functionfs_unbind isn't
bounded so it can go ahead and mark the ep0req to NULL, and since there
is no NULL check in ffs_ep0_queue_wait we will end up in use-after-free.

Fix this by making a serialized execution between the two functions using
a mutex_lock(ffs->mutex).

Fixes: ddf8abd2 ("USB: f_fs: the FunctionFS driver")
Signed-off-by: default avatarUdipto Goswami <quic_ugoswami@quicinc.com>
Tested-by: default avatarKrishna Kurapati <quic_kriskura@quicinc.com>
Link: https://lore.kernel.org/r/20221215052906.8993-2-quic_ugoswami@quicinc.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent edec5067

drivers/usb/gadget/function/f_fs.c

+5 −0
Original line number Diff line number Diff line
@@ -278,6 +278,9 @@ static int __ffs_ep0_queue_wait(struct ffs_data *ffs, char *data, size_t len) 
	struct usb_request *req = ffs->ep0req;

	int ret;



	if (!req)

		return -EINVAL;



	req->zero     = len < le16_to_cpu(ffs->ev.setup.wLength);



	spin_unlock_irq(&ffs->ev.waitq.lock);
@@ -1900,10 +1903,12 @@ static void functionfs_unbind(struct ffs_data *ffs) 
	ENTER();



	if (!WARN_ON(!ffs->gadget)) {

		mutex_lock(&ffs->mutex);

		usb_ep_free_request(ffs->gadget->ep0, ffs->ep0req);

		ffs->ep0req = NULL;

		ffs->gadget = NULL;

		clear_bit(FFS_FL_BOUND, &ffs->flags);

		mutex_unlock(&ffs->mutex);

		ffs_data_put(ffs);

	}

}