USB: yurex: Fix buffer over-read in yurex_write()

If the written data starts with a digit, yurex_write() tries to parse
it as an integer using simple_strtoull().  This requires a null-
terminator, and currently there's no guarantee that there is one.

(The sample program at
https://github.com/NeoCat/YUREX-driver-for-Linux/blob/master/sample/yurex_clock.pl
writes an integer without a null terminator.  It seems like it must
have worked by chance!)

Always add a null byte after the written data.  Enlarge the buffer
to allow for this.

Cc: stable@vger.kernel.org
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c
index 3be40eaa1ac9..1232dd49556d 100644
--- a/drivers/usb/misc/yurex.c
+++ b/drivers/usb/misc/yurex.c
@@ -421,13 +421,13 @@ static ssize_t yurex_write(struct file *file, const char __user *user_buffer,
 {
         struct usb_yurex *dev;
         int i, set = 0, retval = 0;
-        char buffer[16];
+        char buffer[16 + 1];
         char *data = buffer;
         unsigned long long c, c2 = 0;
         signed long timeout = 0;
         DEFINE_WAIT(wait);
 
-        count = min(sizeof(buffer), count);
+        count = min(sizeof(buffer) - 1, count);
         dev = file->private_data;
 
         /* verify that we actually have some data to write */
@@ -446,6 +446,7 @@ static ssize_t yurex_write(struct file *file, const char __user *user_buffer,
                 retval = -EFAULT;
                 goto error;
         }
+        buffer[count] = 0;
         memset(dev->cntl_buffer, CMD_PADDING, YUREX_BUF_SIZE);
 
         switch (buffer[0]) {