[PATCH] char: xillybus: Don't return -EFAULT on user-triggered flush

From: Eli Billauer <eli.billauer@gmail.com>
To: arnd@arndb.de, gregkh@linuxfoundation.org
Cc: linux-kernel@vger.kernel.org, Eli Billauer <eli.billauer@gmail.com>
Subject: [PATCH] char: xillybus: Don't return -EFAULT on user-triggered flush
Date: Fri, 27 Mar 2015 11:56:06 +0300	[thread overview]
Message-ID: <1427446566-17606-1-git-send-email-eli.billauer@gmail.com> (raw)

The API allows the application to flush a host-to-FPGA stream by calling
write() with the data count set to zero. Before this patch, copy_from_user()
was called with a non-zero byte count, which possibly made it attempt to read
from unmapped user memory. Such attempts caused the driver to return -EFAULT
instead of 0, even though the desired operation went through fine.

This patch ensures the driver returns 0 on a successful flush.

Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
---
 drivers/char/xillybus/xillybus_core.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/char/xillybus/xillybus_core.c b/drivers/char/xillybus/xillybus_core.c
index b827fa0..77d6c12 100644
--- a/drivers/char/xillybus/xillybus_core.c
+++ b/drivers/char/xillybus/xillybus_core.c
@@ -1237,6 +1237,8 @@ static ssize_t xillybus_write(struct file *filp, const char __user *userbuf,
 					unsigned char *tail;
 					int i;
 
+					howmany = 0;
+
 					end_offset_plus1 = bufpos >>
 						channel->log2_element_size;
 
-- 
1.7.2.3

