[PATCH v3 1/2] usb: gadget: f_fs: change ep->status safe in ffs_epfile_io()

[Linyu Yuan <quic_linyyuan@xxxxxxxxxxx>]

If a task read/write data in blocking mode, it will wait the completion
in ffs_epfile_io(), if function unbind occurs, ffs_func_unbind() will
kfree ffs ep, once the task wake up, it still dereference the ffs ep to
obtain the request status.

Fix it by moving the request status to io_data which is stack-safe.

Reported-by: Michael Wu <michael@xxxxxxxxxxxxxxxxx>
Reviewed-by: John Keeping <john@xxxxxxxxxxxx>
Signed-off-by: Linyu Yuan <quic_linyyuan@xxxxxxxxxxx>
---
v2: correct interrupted assignment
v3: add Reviewed-by and Reported-by

 drivers/usb/gadget/function/f_fs.c | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 4585ee3..d4d8940 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -122,8 +122,6 @@ struct ffs_ep {
 	struct usb_endpoint_descriptor	*descs[3];
 
 	u8				num;
-
-	int				status;	/* P: epfile->mutex */
 };
 
 struct ffs_epfile {
@@ -227,6 +225,9 @@ struct ffs_io_data {
 	bool use_sg;
 
 	struct ffs_data *ffs;
+
+	int status;
+	struct completion done;
 };
 
 struct ffs_desc_helper {
@@ -707,12 +708,12 @@ static const struct file_operations ffs_ep0_operations = {
 
 static void ffs_epfile_io_complete(struct usb_ep *_ep, struct usb_request *req)
 {
+	struct ffs_io_data *io_data = req->context;
+
 	ENTER();
-	if (req->context) {
-		struct ffs_ep *ep = _ep->driver_data;
-		ep->status = req->status ? req->status : req->actual;
-		complete(req->context);
-	}
+
+	io_data->status = req->status ? req->status : req->actual;
+	complete(&io_data->done);
 }
 
 static ssize_t ffs_copy_to_iter(void *data, int data_len, struct iov_iter *iter)
@@ -1050,7 +1051,6 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 		WARN(1, "%s: data_len == -EINVAL\n", __func__);
 		ret = -EINVAL;
 	} else if (!io_data->aio) {
-		DECLARE_COMPLETION_ONSTACK(done);
 		bool interrupted = false;
 
 		req = ep->req;
@@ -1066,7 +1066,8 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 
 		io_data->buf = data;
 
-		req->context  = &done;
+		init_completion(&io_data->done);
+		req->context  = io_data;
 		req->complete = ffs_epfile_io_complete;
 
 		ret = usb_ep_queue(ep->ep, req, GFP_ATOMIC);
@@ -1075,7 +1076,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 
 		spin_unlock_irq(&epfile->ffs->eps_lock);
 
-		if (wait_for_completion_interruptible(&done)) {
+		if (wait_for_completion_interruptible(&io_data->done)) {
 			/*
 			 * To avoid race condition with ffs_epfile_io_complete,
 			 * dequeue the request first then check
@@ -1083,17 +1084,18 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 			 * condition with req->complete callback.
 			 */
 			usb_ep_dequeue(ep->ep, req);
-			wait_for_completion(&done);
-			interrupted = ep->status < 0;
+			wait_for_completion(&io_data->done);
+			interrupted = io_data->status < 0;
 		}
 
 		if (interrupted)
 			ret = -EINTR;
-		else if (io_data->read && ep->status > 0)
-			ret = __ffs_epfile_read_data(epfile, data, ep->status,
+		else if (io_data->read && io_data->status > 0)
+			ret = __ffs_epfile_read_data(epfile, data, io_data->status,
 						     &io_data->data);
 		else
-			ret = ep->status;
+			ret = io_data->status;
+
 		goto error_mutex;
 	} else if (!(req = usb_ep_alloc_request(ep->ep, GFP_ATOMIC))) {
 		ret = -ENOMEM;
-- 
2.7.4