patch "USB: core: Fix unterminated string returned by usb_string()" added to usb-linus

This is a note to let you know that I've just added the patch titled

USB: core: Fix unterminated string returned by usb_string()

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From c01c348ecdc66085e44912c97368809612231520 Mon Sep 17 00:00:00 2001
From: Alan Stern <[email protected]>
Date: Mon, 15 Apr 2019 11:51:38 -0400
Subject: USB: core: Fix unterminated string returned by usb_string()

Some drivers (such as the vub300 MMC driver) expect usb_string() to return a properly NUL-terminated string, even when an error occurs. (In fact, vub300's probe routine doesn't bother to check the return code from usb_string().) When the driver goes on to use an unterminated string, it leads to kernel errors such as stack-out-of-bounds, as found by the syzkaller USB fuzzer.

An out-of-range string index argument is not at all unlikely, given that some devices don't provide string descriptors and therefore list 0 as the value for their string indexes. This patch makes usb_string() return a properly terminated empty string along with the -EINVAL error code when an out-of-range index is encountered.

And since a USB string index is a single-byte value, indexes >= 256 are just as invalid as values of 0 or below.

---
 drivers/usb/core/message.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

index 82239f27c4cc..e844bb7b5676 100644
@@ -820,9 +820,11 @@ int usb_string(struct usb_device *dev, int index, char *buf, size_t size)
 
 	if (dev->state == USB_STATE_SUSPENDED)
 		return -EHOSTUNREACH;
-	if (size <= 0 || !buf || !index)
+	if (size <= 0 || !buf)
 		return -EINVAL;
 	buf[0] = 0;
+	if (index <= 0 || index >= 256)
+		return -EINVAL;
 	tbuf = kmalloc(256, GFP_NOIO);
 	if (!tbuf)
 		return -ENOMEM;

2.21.0