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usb: gadget: f_fs: Prevent race during ffs_ep0_queue_wait

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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: ddf8abd25994 ("USB: f_fs: the FunctionFS driver")
Signed-off-by: Udipto Goswami <quic_ugoswami@quicinc.com>
Tested-by: Krishna Kurapati <quic_kriskura@quicinc.com>
Link: https://lore.kernel.org/r/20221215052906.8993-2-quic_ugoswami@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Udipto Goswami 2022-12-15 10:59:05 +05:30 committed by Greg Kroah-Hartman
parent cde37881e2
commit 6a19da1110
1 changed files with 5 additions and 0 deletions
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5
drivers/usb/gadget/function/f_fs.c
View File

@ -279,6 +279,9 @@ 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);
@ -1892,10 +1895,12 @@ 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);
}
}