/*      $NetBSD: panic_string.c,v 1.3 2021/10/21 13:21:55 andvar Exp $  */

/*-
 * Copyright (c) 2018 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */


#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: panic_string.c,v 1.3 2021/10/21 13:21:55 andvar Exp $");

#include <sys/param.h>
#include <sys/types.h>
#include <sys/conf.h>
#include <sys/device.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/kmem.h>
#include <sys/lwp.h>
#include <sys/module.h>
#include <sys/vfs_syscalls.h>

/*
 * Create a device /dev/panic from which you can read sequential
 * user input.
 *
 * To use this device you need to do:
 *      mknod /dev/panic c 351 0
 *
 * To write to the device you might need:
 *      chmod 666 /dev/panic
 *
 * Commentary:
 * This module manages the device /dev/panic,
 * transfers a string from userspace to kernel space
 * and calls kernel panic with the passed string.
 *
 *  echo 'string' > /dev/panic
 * will do the trick after loading the module.
 */

dev_type_open(panic_string_open);
dev_type_close(panic_string_close);
dev_type_write(panic_string_write);

static struct cdevsw panic_string_cdevsw = {
        .d_open = panic_string_open,
        .d_close = panic_string_close,
        .d_read = noread,
        .d_write = panic_string_write,
        .d_ioctl = noioctl,
        .d_stop = nostop,
        .d_tty = notty,
        .d_poll = nopoll,
        .d_mmap = nommap,
        .d_kqfilter = nokqfilter,
        .d_discard = nodiscard,
        .d_flag = D_OTHER
};

static struct panic_string_softc {
        int refcnt;
} sc;

/*
 * A function similar to strnlen + isprint
 *
 * Detect length of the printable and non-whitespace string in the buffer.
 * A string is accepted if it contains any non-space character.
 */

static size_t
printable_length(const char *str, size_t len)
{
        size_t n;       
        bool accepted;

        n = 0;
        accepted = false;

        while (len > n) {
                if (str[n] >= 0x20 && str[n] <= 0x7e) {
                        if (str[n] != 0x20 /* space */)
                                accepted = true;
                        n++;
                } else
                        break;
        }

        if (accepted)
                return n;
        else
                return 0;
}

int
panic_string_open(dev_t self __unused, int flag __unused, int mod __unused, struct lwp *l)
{

        /* Make sure the device is opened once at a time */
        if (sc.refcnt > 0)
                return EBUSY;

        ++sc.refcnt;

        return 0;
}

int
panic_string_close(dev_t self __unused, int flag __unused, int mod __unused, struct lwp *l __unused)
{

        --sc.refcnt;
        return 0;
}

int
panic_string_write(dev_t self, struct uio *uio, int flags)
{
        size_t len, printlen;
        char *buffer;

        /* Buffer length */
        len = uio->uio_iov->iov_len;

        /* Allocate a local buffer to store the string */
        buffer = (char *)kmem_alloc(len, KM_SLEEP);

        /* Move the string from user to kernel space and store it locally */
        uiomove(buffer, len, uio);

        printlen = printable_length(buffer, len);

        if (printlen > 0) {
                /* Flushing disk changes */
                do_sys_sync(curlwp);

                panic("panic string: %.*s\n", (int)printlen, buffer);
//              printf("panic string: %.*s\n", (int)printlen, buffer);

                /* NOTREACHED */
        }

        kmem_free(buffer, len);
        return 0;
}

MODULE(MODULE_CLASS_MISC, panic_string, NULL);

static int
panic_string_modcmd(modcmd_t cmd, void *arg __unused)
{
        /* The major should be verified and changed if needed to avoid
         * conflicts with other devices. */
        int cmajor = 351, bmajor = -1;

        switch (cmd) {
        case MODULE_CMD_INIT:
                printf("Panic String module loaded.\n");
                if (devsw_attach("panic", NULL, &bmajor, &panic_string_cdevsw,
                                                 &cmajor))
                        return ENXIO;
                return 0;

        case MODULE_CMD_FINI:
                printf("Panic String module unloaded.\n");
                if (sc.refcnt > 0)
                        return EBUSY;

                devsw_detach(NULL, &panic_string_cdevsw);
                return 0;
        default:
                return ENOTTY;
        }
}