linux-kernel - [PATCH v2] usb: gadget: return the right length in ffs_epfile

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Message-Id: <1393918497-30916-1-git-send-email-chuansheng.liu@intel.com>
Date:	Tue,  4 Mar 2014 15:34:57 +0800
From:	Chuansheng Liu <chuansheng.liu@...el.com>
To:	balbi@...com, gregkh@...uxfoundation.org
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	mina86@...a86.com, david.a.cohen@...ux.intel.com,
	Chuansheng Liu <chuansheng.liu@...el.com>
Subject: [PATCH v2] usb: gadget: return the right length in ffs_epfile_io()

When the request length is aligned to maxpacketsize, sometimes
the return length ret > the user space requested len.

At that time, we will use min_t(size_t, ret, len) to limit the
size in case of user data buffer overflow.

But we need return the min_t(size_t, ret, len) to tell the user
space rightly also.

Acked-by: Michal Nazarewicz <mina86@...a86.com>
Reviewed-by: David Cohen <david.a.cohen@...ux.intel.com>
Signed-off-by: Chuansheng Liu <chuansheng.liu@...el.com>
---
 drivers/usb/gadget/f_fs.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c
index 42f7a0e..780f877 100644
--- a/drivers/usb/gadget/f_fs.c
+++ b/drivers/usb/gadget/f_fs.c
@@ -845,12 +845,14 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 			 * we may end up with more data then user space has
 			 * space for.
 			 */
-			ret = ep->status;
-			if (io_data->read && ret > 0 &&
-			    unlikely(copy_to_user(io_data->buf, data,
-						  min_t(size_t, ret,
-						  io_data->len))))
-				ret = -EFAULT;
+				ret = ep->status;
+				if (io_data->read && ret > 0) {
+					ret = min_t(size_t, ret, io_data->len);
+
+					if (unlikely(copy_to_user(io_data->buf,
+						data, ret)))
+						ret = -EFAULT;
+				}
 			}
 			kfree(data);
 		}
-- 
1.9.rc0

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