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). Also, dequeue the ep0req to ensure that no
other function can use it after the free operation.
Fixes: ddf8abd25994 ("USB: f_fs: the FunctionFS driver")
Signed-off-by: Udipto Goswami <quic_ugoswami@xxxxxxxxxxx>
---
v3: Moved dequeue out of mutex to prevent deadlock
drivers/usb/gadget/function/f_fs.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 73dc10a77cde..523a961b910b 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -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 +1895,14 @@ static void functionfs_unbind(struct ffs_data *ffs)
ENTER();
if (!WARN_ON(!ffs->gadget)) {
+ /* dequeue before freeing ep0req */
+ usb_ep_dequeue(ffs->gadget->ep0, ffs->ep0req);
+ 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);
}
}
--
2.17.1
