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    Subject[PATCH 4.4 118/266] USB: core: Fix unterminated string returned by usb_string()
    Date
    From: Alan Stern <stern@rowland.harvard.edu>

    commit c01c348ecdc66085e44912c97368809612231520 upstream.

    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>

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

    --- a/drivers/usb/core/message.c
    +++ b/drivers/usb/core/message.c
    @@ -820,9 +820,11 @@ int usb_string(struct usb_device *dev, i

    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;

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