[PATCH v2] usb: ffs: fix regression when quirk_ep_out_aligned_size flag is set

[David Cohen <david.a.cohen@linux.intel.com>]

The commit '2e4c7553cd usb: gadget: f_fs: add aio support' broke the
quirk implemented to align buffer size to maxpacketsize on out endpoint.
As result, functionfs does not work on Intel platforms using dwc3 driver
(i.e. Bay Trail and Merrifield). This patch fixes the issue.

This code is based on a previous Qiuxu's patch.

Fixes: 2e4c7553cd (usb: gadget: f_fs: add aio support)
Cc: <stable@vger.kernel.org> # v3.16+
Signed-off-by: David Cohen <david.a.cohen@linux.intel.com>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
---

Hi,

Since this is a feature that worked in past, this is meant for stable
versions >= 3.16 too.

v1 to v2: just added Fixes, Cc and Acked-by lines on patch description.

Br, David Cohen

---
 drivers/usb/gadget/function/f_fs.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 0dc3552d1360..6e2b8063b170 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -648,15 +648,26 @@ static void ffs_user_copy_worker(struct work_struct *work)
 	if (io_data->read && ret > 0) {
 		int i;
 		size_t pos = 0;
+
+		/*
+		 * Since req->length may be bigger than io_data->len (after
+		 * being rounded up to maxpacketsize), we may end up with more
+		 * data then user space has space for.
+		 */
+		ret = min_t(int, ret, io_data->len);
+
 		use_mm(io_data->mm);
 		for (i = 0; i < io_data->nr_segs; i++) {
+			size_t len = min_t(size_t, ret - pos,
+					io_data->iovec[i].iov_len);
+			if (!len)
+				break;
 			if (unlikely(copy_to_user(io_data->iovec[i].iov_base,
-						 &io_data->buf[pos],
-						 io_data->iovec[i].iov_len))) {
+						 &io_data->buf[pos], len))) {
 				ret = -EFAULT;
 				break;
 			}
-			pos += io_data->iovec[i].iov_len;
+			pos += len;
 		}
 		unuse_mm(io_data->mm);
 	}
@@ -794,7 +805,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 				goto error_lock;
 
 			req->buf      = data;
-			req->length   = io_data->len;
+			req->length   = data_len;
 
 			io_data->buf = data;
 			io_data->ep = ep->ep;
@@ -816,7 +827,7 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 
 			req = ep->req;
 			req->buf      = data;
-			req->length   = io_data->len;
+			req->length   = data_len;
 
 			req->context  = &done;
 			req->complete = ffs_epfile_io_complete;
-- 
2.1.0