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When used function put_cmsg() to copy kernel information to user 
application memory, if the memory length given by user application is 
not enough, by the bad length calculate of msg.msg_controllen, 
put_cmsg() function may cause the msg.msg_controllen to be a large 
value, such as 0xFFFFFFF0, so the following put_cmsg() can also write 
data to usr application memory even usr has no valid memory to store 
this. This may cause usr application memory overflow.

int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
{
    struct cmsghdr __user *cm
        = (__force struct cmsghdr __user *)msg->msg_control;
    struct cmsghdr cmhdr;
    int cmlen = CMSG_LEN(len);
    ~~~~~~~~~~~~~~~~~~~~~
    int err;

    if (MSG_CMSG_COMPAT & msg->msg_flags)
        return put_cmsg_compat(msg, level, type, len, data);

    if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
        msg->msg_flags |= MSG_CTRUNC;
        ret...