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    Subject[PATCH 4.14 014/178] USB: core: prevent malicious bNumInterfaces overflow
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Alan Stern <stern@rowland.harvard.edu>

    commit 48a4ff1c7bb5a32d2e396b03132d20d552c0eca7 upstream.

    A malicious USB device with crafted descriptors can cause the kernel
    to access unallocated memory by setting the bNumInterfaces value too
    high in a configuration descriptor. Although the value is adjusted
    during parsing, this adjustment is skipped in one of the error return
    paths.

    This patch prevents the problem by setting bNumInterfaces to 0
    initially. The existing code already sets it to the proper value
    after parsing is complete.

    Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
    Reported-by: Andrey Konovalov <andreyknvl@google.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

    --- a/drivers/usb/core/config.c
    +++ b/drivers/usb/core/config.c
    @@ -555,6 +555,9 @@ static int usb_parse_configuration(struc
    unsigned iad_num = 0;

    memcpy(&config->desc, buffer, USB_DT_CONFIG_SIZE);
    + nintf = nintf_orig = config->desc.bNumInterfaces;
    + config->desc.bNumInterfaces = 0; // Adjusted later
    +
    if (config->desc.bDescriptorType != USB_DT_CONFIG ||
    config->desc.bLength < USB_DT_CONFIG_SIZE ||
    config->desc.bLength > size) {
    @@ -568,7 +571,6 @@ static int usb_parse_configuration(struc
    buffer += config->desc.bLength;
    size -= config->desc.bLength;

    - nintf = nintf_orig = config->desc.bNumInterfaces;
    if (nintf > USB_MAXINTERFACES) {
    dev_warn(ddev, "config %d has too many interfaces: %d, "
    "using maximum allowed: %d\n",

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