Patch "usb: gadget: f_fs: Fix EFAULT generation for async read operations" has been added to the 4.5-stable tree

This is a note to let you know that I've just added the patch titled

usb: gadget: f_fs: Fix EFAULT generation for async read operations

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-gadget-f_fs-fix-efault-generation-for-async-read-operations.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Lars-Peter Clausen <[email protected]>
Date: Wed, 30 Mar 2016 13:49:14 +0200
Subject: usb: gadget: f_fs: Fix EFAULT generation for async read operations

From: Lars-Peter Clausen <[email protected]>

commit 332a5b446b7916d272c2a659a3b20909ce34d2c1 upstream.

In the current implementation functionfs generates a EFAULT for async read operations if the read buffer size is larger than the URB data size. Since a application does not necessarily know how much data the host side is going to send it typically supplies a buffer larger than the actual data, which will then result in a EFAULT error.

This behaviour was introduced while refactoring the code to use iov_iter interface in commit c993c39b8639 ("gadget/function/f_fs.c: use put iov_iter into io_data"). The original code took the minimum over the URB size and the user buffer size and then attempted to copy that many bytes using copy_to_user(). If copy_to_user() could not copy all data a EFAULT error was generated. Restore the original behaviour by only generating a EFAULT error when the number of bytes copied is not the size of the URB and the target buffer has not been fully filled.

Commit 342f39a6c8d3 ("usb: gadget: f_fs: fix check in read operation") already fixed the same problem for the synchronous read path.

---
 drivers/usb/gadget/function/f_fs.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -651,7 +651,7 @@ static void ffs_user_copy_worker(struct
 	if (io_data->read && ret > 0) {
 		use_mm(io_data->mm);
 		ret = copy_to_iter(io_data->buf, ret, &io_data->data);
-		if (iov_iter_count(&io_data->data))
+		if (ret != io_data->req->actual && iov_iter_count(&io_data->data))
 			ret = -EFAULT;
 		unuse_mm(io_data->mm);
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/usb-gadget-f_fs-fix-efault-generation-for-async-read-operations.patch