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.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: syzbot+b75b85111c10b8d680f1@syzkaller.appspotmail.com
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 82239f27c4ccf822daca19fe2e9c6cffb19933c7..e844bb7b5676a4525724d25883231af474cdd8e0 100644 (file)
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -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;