[PATCH 3.16 197/328] USB: yurex: Fix buffer over-read in yurex_write()

Ben Hutchings
2018-12-09T22:04:41Z

From: Ben Hutchings <ben.hutchings@codethink.co.uk>

commit 7e10f14ebface44a48275c8d6dc1caae3668d5a9 upstream.

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.

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/usb/misc/yurex.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/usb/misc/yurex.c
+++ b/drivers/usb/misc/yurex.c
@@ -437,13 +437,13 @@ static ssize_t yurex_write(struct file *
{
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 = (struct usb_yurex *)file->private_data;

/* verify that we actually have some data to write */
@@ -462,6 +462,7 @@ static ssize_t yurex_write(struct file *
retval = -EFAULT;
goto error;
}
+ buffer[count] = 0;
memset(dev->cntl_buffer, CMD_PADDING, YUREX_BUF_SIZE);

switch (buffer[0]) {