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

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Message-Id: <1393483771-24623-1-git-send-email-chuansheng.liu@intel.com>
Date:	Thu, 27 Feb 2014 14:49:31 +0800
From:	Chuansheng Liu <chuansheng.liu@...el.com>
To:	balbi@...com, gregkh@...uxfoundation.org, mina86@...a86.com
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	david.a.cohen@...el.com, jin.can.zhuang@...el.com,
	yu.y.wang@...el.com, Chuansheng Liu <chuansheng.liu@...el.com>
Subject: [PATCH] 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.

Signed-off-by: Chuansheng Liu <chuansheng.liu@...el.com>
---
 drivers/usb/gadget/f_fs.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c
index 2b43343..31ee7af 100644
--- a/drivers/usb/gadget/f_fs.c
+++ b/drivers/usb/gadget/f_fs.c
@@ -687,10 +687,12 @@ static ssize_t ffs_epfile_io(struct file *file,
 			 * space for.
 			 */
 			ret = ep->status;
-			if (read && ret > 0 &&
-			    unlikely(copy_to_user(buf, data,
-						  min_t(size_t, ret, len))))
-				ret = -EFAULT;
+			if (read && ret > 0) {
+				ret = min_t(size_t, ret, len);
+
+				if (unlikely(copy_to_user(buf, data, ret)))
+					ret = -EFAULT;
+			}
 		}
 	}
 
-- 
1.9.rc0

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