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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        "Ben Hutchings" <ben.hutchings@codethink.co.uk>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
Message-ID: <lsq.1544392233.415106178@decadent.org.uk>
Subject: [PATCH 3.16 197/328] USB: yurex: Fix buffer over-read in
 yurex_write()
In-Reply-To: <lsq.1544392232.713909046@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

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

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]) {