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    Subject[PATCH 4.4 079/230] media: uvcvideo: Fix type check leading to overflow
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Alistair Strachan <astrachan@google.com>

    commit 47bb117911b051bbc90764a8bff96543cbd2005f upstream.

    When initially testing the Camera Terminal Descriptor wTerminalType
    field (buffer[4]), no mask is used. Later in the function, the MSB is
    overloaded to store the descriptor subtype, and so a mask of 0x7fff
    is used to check the type.

    If a descriptor is specially crafted to set this overloaded bit in the
    original wTerminalType field, the initial type check will fail (falling
    through, without adjusting the buffer size), but the later type checks
    will pass, assuming the buffer has been made suitably large, causing an
    overflow.

    Avoid this problem by checking for the MSB in the wTerminalType field.
    If the bit is set, assume the descriptor is bad, and abort parsing it.

    Originally reported here:
    https://groups.google.com/forum/#!topic/syzkaller/Ot1fOE6v1d8
    A similar (non-compiling) patch was provided at that time.

    Reported-by: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: Alistair Strachan <astrachan@google.com>
    Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
    Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/media/usb/uvc/uvc_driver.c | 14 +++++++++++---
    1 file changed, 11 insertions(+), 3 deletions(-)

    --- a/drivers/media/usb/uvc/uvc_driver.c
    +++ b/drivers/media/usb/uvc/uvc_driver.c
    @@ -1019,11 +1019,19 @@ static int uvc_parse_standard_control(st
    return -EINVAL;
    }

    - /* Make sure the terminal type MSB is not null, otherwise it
    - * could be confused with a unit.
    + /*
    + * Reject invalid terminal types that would cause issues:
    + *
    + * - The high byte must be non-zero, otherwise it would be
    + * confused with a unit.
    + *
    + * - Bit 15 must be 0, as we use it internally as a terminal
    + * direction flag.
    + *
    + * Other unknown types are accepted.
    */
    type = get_unaligned_le16(&buffer[4]);
    - if ((type & 0xff00) == 0) {
    + if ((type & 0x7f00) == 0 || (type & 0x8000) != 0) {
    uvc_trace(UVC_TRACE_DESCR, "device %d videocontrol "
    "interface %d INPUT_TERMINAL %d has invalid "
    "type 0x%04x, skipping\n", udev->devnum,

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