linux-kernel - [PATCH 4.18 131/235] USB: yurex: Fix buffer over-read in yurex

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Message-Id: <20180924113118.976640186@linuxfoundation.org>
Date:   Mon, 24 Sep 2018 13:51:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>
Subject: [PATCH 4.18 131/235] USB: yurex: Fix buffer over-read in yurex_write()

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben.hutchings@...ethink.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.

Cc: stable@...r.kernel.org
Signed-off-by: Ben Hutchings <ben.hutchings@...ethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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
@@ -421,13 +421,13 @@ 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 = file->private_data;
 
 	/* verify that we actually have some data to write */
@@ -446,6 +446,7 @@ 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]) {