/**
 * BSD Secure Levels LSM
 *
 * Maintainers:
 *      Michael A. Halcrow <mike@halcrow.us>
 *      Serge Hallyn <hallyn@cs.wm.edu>
 *
 * Copyright (c) 2001 WireX Communications, Inc <chris@wirex.com>
 * Copyright (c) 2001 Greg Kroah-Hartman <greg@kroah.com>
 * Copyright (c) 2002 International Business Machines <robb@austin.ibm.com>
 * Copyright (c) 2006 Davi E. M. Arnaut <davi.arnaut@gmail.com>
 *
 *      This program is free software; you can redistribute it and/or modify
 *      it under the terms of the GNU General Public License as published by
 *      the Free Software Foundation; either version 2 of the License, or
 *      (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/security.h>
#include <linux/netlink.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/capability.h>
#include <linux/time.h>
#include <linux/proc_fs.h>
#include <linux/kobject.h>
#include <linux/crypto.h>
#include <asm/scatterlist.h>
#include <linux/scatterlist.h>
#include <linux/gfp.h>
#include <linux/sysfs.h>

#define SHA1_DIGEST_SIZE 20

/**
 * Module parameter that defines the initial secure level.
 *
 * When built as a module, it defaults to seclvl 1, which is the
 * behavior of BSD secure levels.  Note that this default behavior
 * wrecks havoc on a machine when the seclvl module is compiled into
 * the kernel.  In that case, we default to seclvl 0.
 */
#ifdef CONFIG_SECURITY_SECLVL_MODULE
static int initlvl = 1;
#else
static int initlvl;
#endif
module_param(initlvl, int, 0);
MODULE_PARM_DESC(initlvl, "Initial secure level (defaults to 1)");

/* Module parameter that defines the verbosity level */
static int verbosity;
module_param(verbosity, int, 0);
MODULE_PARM_DESC(verbosity, "Initial verbosity level (0 or 1; defaults to "
                 "0, which is Quiet)");

/**
 * Optional password which can be passed in to bring seclvl to 0
 * (i.e., for halt/reboot).  Defaults to NULL (the passwd attribute
 * file will not be registered in sysfs).
 *
 * This gets converted to its SHA1 hash when stored.  It's probably
 * not a good idea to use this parameter when loading seclvl from a
 * script; use sha1_passwd instead.
 */

#define MAX_PASSWD_SIZE 32
static char passwd[MAX_PASSWD_SIZE];
module_param_string(passwd, passwd, sizeof(passwd), 0);
MODULE_PARM_DESC(passwd,
                 "Plaintext of password that sets seclvl=0 when written to "
                 "(sysfs mount point)/seclvl/passwd\n");

/**
 * SHA1 hashed version of the optional password which can be passed in
 * to bring seclvl to 0 (i.e., for halt/reboot).  Must be in
 * hexadecimal format (40 characters).  Defaults to NULL (the passwd
 * attribute file will not be registered in sysfs).
 *
 * Use the sha1sum utility to generate the SHA1 hash of a password:
 *
 * echo -n "secret" | sha1sum
 */
#define MAX_SHA1_PASSWD 41
static char sha1_passwd[MAX_SHA1_PASSWD];
module_param_string(sha1_passwd, sha1_passwd, sizeof(sha1_passwd), 0);
MODULE_PARM_DESC(sha1_passwd,
                 "SHA1 hash (40 hexadecimal characters) of password that "
                 "sets seclvl=0 when plaintext password is written to "
                 "(sysfs mount point)/seclvl/passwd\n");

static int hideHash = 1;
module_param(hideHash, int, 0);
MODULE_PARM_DESC(hideHash, "When set to 0, reading seclvl/passwd from sysfs "
                 "will return the SHA1-hashed value of the password that "
                 "lowers the secure level to 0.\n");

#define MY_NAME "seclvl"

/**
 * This time-limits log writes to one per second.
 */
#define seclvl_printk(verb, type, fmt, arg...)                  \
        do {                                                    \
                if (verbosity >= verb) {                        \
                        static unsigned long _prior;            \
                        unsigned long _now = jiffies;           \
                        if ((_now - _prior) > HZ) {             \
                                printk(type "%s: %s: " fmt,     \
                                        MY_NAME, __FUNCTION__ , \
                                        ## arg);                \
                                _prior = _now;                  \
                        }                                       \
                }                                               \
        } while (0)

/**
 * The actual security level.  Ranges between -1 and 2 inclusive.
 */
static int seclvl;

/**
 * flag to keep track of how we were registered
 */
static int secondary;

/**
 * Verifies that the requested secure level is valid, given the current
 * secure level.
 */
static int seclvl_sanity(int reqlvl)
{
        if ((reqlvl < -1) || (reqlvl > 2)) {
                seclvl_printk(1, KERN_WARNING, "Attempt to set seclvl out of "
                              "range: [%d]\n", reqlvl);
                return -EINVAL;
        }
        if ((seclvl == 0) && (reqlvl == -1))
                return 0;
        if (reqlvl < seclvl) {
                seclvl_printk(1, KERN_WARNING, "Attempt to lower seclvl to "
                              "[%d]\n", reqlvl);
                return -EPERM;
        }
        return 0;
}

/**
 * security level advancement rules:
 *   Valid levels are -1 through 2, inclusive.
 *   From -1, stuck.  [ in case compiled into kernel ]
 *   From 0 or above, can only increment.
 */
static void do_seclvl_advance(void *data, u64 val)
{
        int ret;
        int newlvl = (int)val;

        ret = seclvl_sanity(newlvl);
        if (ret)
                return;

        if (newlvl > 2) {
                seclvl_printk(1, KERN_WARNING, "Cannot advance to seclvl "
                              "[%d]\n", newlvl);
                return;
        }
        if (seclvl == -1) {
                seclvl_printk(1, KERN_WARNING, "Not allowed to advance to "
                              "seclvl [%d]\n", seclvl);
                return;
        }
        seclvl = newlvl;  /* would it be more "correct" to set *data? */
        return;
}

static u64 seclvl_int_get(void *data)
{
        return *(int *)data;
}

DEFINE_SIMPLE_ATTRIBUTE(seclvl_file_ops, seclvl_int_get, do_seclvl_advance, "%lld\n");

static unsigned char hashedPassword[SHA1_DIGEST_SIZE];

/**
 * Converts a block of plaintext of into its SHA1 hashed value.
 *
 * It would be nice if crypto had a wrapper to do this for us linear
 * people...
 */
static int
plaintext_to_sha1(unsigned char *hash, const char *plaintext, unsigned int len)
{
        struct crypto_tfm *tfm;
        struct scatterlist sg;
        if (len > PAGE_SIZE) {
                seclvl_printk(0, KERN_ERR, "Plaintext password too large (%d "
                              "characters).  Largest possible is %lu "
                              "bytes.\n", len, PAGE_SIZE);
                return -EINVAL;
        }
        tfm = crypto_alloc_tfm("sha1", CRYPTO_TFM_REQ_MAY_SLEEP);
        if (tfm == NULL) {
                seclvl_printk(0, KERN_ERR,
                              "Failed to load transform for SHA1\n");
                return -EINVAL;
        }
        sg_init_one(&sg, (u8 *)plaintext, len);
        crypto_digest_init(tfm);
        crypto_digest_update(tfm, &sg, 1);
        crypto_digest_final(tfm, hash);
        crypto_free_tfm(tfm);
        return 0;
}

/**
 * Called whenever the user writes to the sysfs passwd handle to this kernel
 * object.  It hashes the password and compares the hashed results.
 */
static ssize_t
passwd_write_file(struct file * file, const char __user * buf,
                                size_t count, loff_t *ppos)
{
        char *p;
        int len;
        unsigned char tmp[SHA1_DIGEST_SIZE];

        if (!*passwd && !*sha1_passwd) {
                seclvl_printk(0, KERN_ERR, "Attempt to password-unlock the "
                              "seclvl module, but neither a plain text "
                              "password nor a SHA1 hashed password was "
                              "passed in as a module parameter!  This is a "
                              "bug, since it should not be possible to be in "
                              "this part of the module; please tell a "
                              "maintainer about this event.\n");
                return -EINVAL;
        }

        if (count >= PAGE_SIZE)
                return -EINVAL;
        if (*ppos != 0)
                return -EINVAL;
        p = kmalloc(count, GFP_KERNEL);
        if (!p)
                return -ENOMEM;
        len = -EFAULT;
        if (copy_from_user(p, buf, count))
                goto out;
        
        len = count;
        /* ``echo "secret" > seclvl/passwd'' includes a newline */
        if (p[len - 1] == '\n')
                len--;
        /* Hash the password, then compare the hashed values */
        if ((len = plaintext_to_sha1(tmp, p, len))) {
                seclvl_printk(0, KERN_ERR, "Error hashing password: rc = "
                              "[%d]\n", len);
                goto out;
        }

        len = -EPERM;
        if (memcmp(hashedPassword, tmp, SHA1_DIGEST_SIZE))
                goto out;

        seclvl_printk(0, KERN_INFO,
                      "Password accepted; seclvl reduced to 0.\n");
        seclvl = 0;
        len = count;

out:
        kfree (p);
        return len;
}

static struct file_operations passwd_file_ops = {
        .write = passwd_write_file,
};

/**
 * Explicitely disallow ptrace'ing the init process.
 */
static int seclvl_ptrace(struct task_struct *parent, struct task_struct *child)
{
        if (seclvl >= 0 && child->pid == 1) {
                seclvl_printk(1, KERN_WARNING, "Attempt to ptrace "
                              "the init process dissallowed in "
                              "secure level %d\n", seclvl);
                return -EPERM;
        }
        return 0;
}

/**
 * Capability checks for seclvl.  The majority of the policy
 * enforcement for seclvl takes place here.
 */
static int seclvl_capable(struct task_struct *tsk, int cap)
{
        int rc = 0;

        /* init can do anything it wants */
        if (tsk->pid == 1)
                return 0;

        if (seclvl > 0) {
                rc = -EPERM;

                if (cap == CAP_LINUX_IMMUTABLE)
                        seclvl_printk(1, KERN_WARNING, "Attempt to modify "
                                      "the IMMUTABLE and/or APPEND extended "
                                      "attribute on a file with the IMMUTABLE "
                                      "and/or APPEND extended attribute set "
                                      "denied in seclvl [%d]\n", seclvl);
                else if (cap == CAP_SYS_RAWIO)
                        seclvl_printk(1, KERN_WARNING, "Attempt to perform "
                                      "raw I/O while in secure level [%d] "
                                      "denied\n", seclvl);
                else if (cap == CAP_NET_ADMIN)
                        seclvl_printk(1, KERN_WARNING, "Attempt to perform "
                                      "network administrative task while "
                                      "in secure level [%d] denied\n", seclvl);
                else if (cap == CAP_SETUID)
                        seclvl_printk(1, KERN_WARNING, "Attempt to setuid "
                                      "while in secure level [%d] denied\n",
                                      seclvl);
                else if (cap == CAP_SETGID)
                        seclvl_printk(1, KERN_WARNING, "Attempt to setgid "
                                      "while in secure level [%d] denied\n",
                                      seclvl);
                else if (cap == CAP_SYS_MODULE)
                        seclvl_printk(1, KERN_WARNING, "Attempt to perform "
                                      "a module operation while in secure "
                                      "level [%d] denied\n", seclvl);
                else
                        rc = 0;
        }

        if (!rc) {
                if (!(cap_is_fs_cap(cap) ? tsk->fsuid == 0 : tsk->euid == 0))
                        rc = -EPERM;
        }

        if (rc)
                seclvl_printk(1, KERN_WARNING, "Capability denied\n");

        return rc;
}

/**
 * Disallow reversing the clock in seclvl > 1
 */
static int seclvl_settime(struct timespec *tv, struct timezone *tz)
{
        if (tv && seclvl > 1) {
                struct timespec now;
                now = current_kernel_time();
                if (tv->tv_sec < now.tv_sec ||
                    (tv->tv_sec == now.tv_sec && tv->tv_nsec < now.tv_nsec)) {
                        seclvl_printk(1, KERN_WARNING, "Attempt to decrement "
                                      "time in secure level %d denied: "
                                      "current->pid = [%d], "
                                      "current->group_leader->pid = [%d]\n",
                                      seclvl, current->pid,
                                      current->group_leader->pid);
                        return -EPERM;
                }               /* if attempt to decrement time */
        }                       /* if seclvl > 1 */
        return 0;
}

/* claim the blockdev to exclude mounters, release on file close */
static int seclvl_bd_claim(struct inode *inode)
{
        int holder;
        struct block_device *bdev = NULL;
        dev_t dev = inode->i_rdev;
        bdev = open_by_devnum(dev, FMODE_WRITE);
        if (bdev) {
                if (bd_claim(bdev, &holder)) {
                        blkdev_put(bdev);
                        return -EPERM;
                }
                /* claimed, mark it to release on close */
                inode->i_security = current;
        }
        return 0;
}

/* release the blockdev if you claimed it */
static void seclvl_bd_release(struct inode *inode)
{
        if (inode && S_ISBLK(inode->i_mode) && inode->i_security == current) {
                struct block_device *bdev = inode->i_bdev;
                if (bdev) {
                        bd_release(bdev);
                        blkdev_put(bdev);
                        inode->i_security = NULL;
                }
        }
}

/**
 * Security for writes to block devices is regulated by this seclvl
 * function.  Deny all writes to block devices in seclvl 2.  In
 * seclvl 1, we only deny writes to *mounted* block devices.
 */
static int
seclvl_inode_permission(struct inode *inode, int mask, struct nameidata *nd)
{
        if (current->pid != 1 && S_ISBLK(inode->i_mode) && (mask & MAY_WRITE)) {
                switch (seclvl) {
                case 2:
                        seclvl_printk(1, KERN_WARNING, "Write to block device "
                                      "denied in secure level [%d]\n", seclvl);
                        return -EPERM;
                case 1:
                        if (seclvl_bd_claim(inode)) {
                                seclvl_printk(1, KERN_WARNING,
                                              "Write to mounted block device "
                                              "denied in secure level [%d]\n",
                                              seclvl);
                                return -EPERM;
                        }
                }
        }
        return 0;
}

/**
 * The SUID and SGID bits cannot be set in seclvl >= 1
 */
static int seclvl_inode_setattr(struct dentry *dentry, struct iattr *iattr)
{
        if (seclvl > 0) {
                if (iattr->ia_valid & ATTR_MODE)
                        if (iattr->ia_mode & S_ISUID ||
                            iattr->ia_mode & S_ISGID) {
                                seclvl_printk(1, KERN_WARNING, "Attempt to "
                                              "modify SUID or SGID bit "
                                              "denied in seclvl [%d]\n",
                                              seclvl);
                                return -EPERM;
                        }
        }
        return 0;
}

/* release busied block devices */
static void seclvl_file_free_security(struct file *filp)
{
        struct dentry *dentry = filp->f_dentry;

        if (dentry)
                seclvl_bd_release(dentry->d_inode);
}

/**
 * Cannot unmount in secure level 2
 */
static int seclvl_umount(struct vfsmount *mnt, int flags)
{
        if (current->pid != 1 && seclvl == 2) {
                seclvl_printk(1, KERN_WARNING, "Attempt to unmount in secure "
                              "level %d\n", seclvl);
                return -EPERM;
        }
        return 0;
}

static struct security_operations seclvl_ops = {
        .ptrace = seclvl_ptrace,
        .capable = seclvl_capable,
        .inode_permission = seclvl_inode_permission,
        .inode_setattr = seclvl_inode_setattr,
        .file_free_security = seclvl_file_free_security,
        .settime = seclvl_settime,
        .sb_umount = seclvl_umount,
};

/**
 * Process the password-related module parameters
 */
static int processPassword(void)
{
        int rc = 0;
        if (*passwd) {
                char *p;

                if (*sha1_passwd) {
                        seclvl_printk(0, KERN_ERR, "Error: Both "
                                      "passwd and sha1_passwd "
                                      "were set, but they are mutually "
                                      "exclusive.\n");
                        return -EINVAL;
                }

                p = kstrdup(passwd, GFP_KERNEL);
                if (p == NULL)
                        return -ENOMEM;

                if ((rc = plaintext_to_sha1(hashedPassword, p, strlen(p))))
                        seclvl_printk(0, KERN_ERR, "Error: SHA1 support not "
                                      "in kernel\n");

                kfree (p);
                /* All static data goes to the BSS, which zero's the
                 * plaintext password out for us. */
        } else if (*sha1_passwd) {      // Base 16
                int i;
                i = strlen(sha1_passwd);
                if (i != (SHA1_DIGEST_SIZE * 2)) {
                        seclvl_printk(0, KERN_ERR, "Received [%d] bytes; "
                                      "expected [%d] for the hexadecimal "
                                      "representation of the SHA1 hash of "
                                      "the password.\n",
                                      i, (SHA1_DIGEST_SIZE * 2));
                        return -EINVAL;
                }
                while ((i -= 2) + 2) {
                        unsigned char tmp;
                        tmp = sha1_passwd[i + 2];
                        sha1_passwd[i + 2] = '\0';
                        hashedPassword[i / 2] = (unsigned char)
                            simple_strtol(&sha1_passwd[i], NULL, 16);
                        sha1_passwd[i + 2] = tmp;
                }
        }
        return rc;
}

/**
 * securityfs registrations
 */
struct dentry *dir_ino, *seclvl_ino, *passwd_ino;

static int seclvlfs_register(void)
{
        int rc = 0;

        dir_ino = securityfs_create_dir("seclvl", NULL);

        if (IS_ERR(dir_ino))
                return PTR_ERR(dir_ino);

        seclvl_ino = securityfs_create_file("seclvl", S_IRUGO | S_IWUSR,
                                dir_ino, &seclvl, &seclvl_file_ops);
        if (IS_ERR(seclvl_ino)) {
                rc = PTR_ERR(seclvl_ino);
                goto out_deldir;
        }
        if (*passwd || *sha1_passwd) {
                passwd_ino = securityfs_create_file("passwd", S_IRUGO | S_IWUSR,
                                dir_ino, NULL, &passwd_file_ops);
                if (IS_ERR(passwd_ino)) {
                        rc = PTR_ERR(passwd_ino);
                        goto out_delf;
                }
        }
        return rc;

out_delf:
        securityfs_remove(seclvl_ino);

out_deldir:
        securityfs_remove(dir_ino);

        return rc;
}

static void seclvlfs_unregister(void)
{
        securityfs_remove(seclvl_ino);

        if (*passwd || *sha1_passwd)
                securityfs_remove(passwd_ino);

        securityfs_remove(dir_ino);
}

/**
 * Initialize the seclvl module.
 */
static int __init seclvl_init(void)
{
        int rc = 0;
        static char once;

        if (verbosity < 0 || verbosity > 1) {
                printk(KERN_ERR "Error: bad verbosity [%d]; only 0 or 1 "
                       "are valid values\n", verbosity);
                rc = -EINVAL;
                goto exit;
        }
        if (initlvl < -1 || initlvl > 2) {
                seclvl_printk(0, KERN_ERR, "Error: bad initial securelevel "
                              "[%d].\n", initlvl);
                rc = -EINVAL;
                goto exit;
        }
        seclvl = initlvl;
        if ((rc = processPassword())) {
                seclvl_printk(0, KERN_ERR, "Error processing the password "
                              "module parameter(s): rc = [%d]\n", rc);
                goto exit;
        }

        if ((rc = seclvlfs_register())) {
                seclvl_printk(0, KERN_ERR, "Error registering with sysfs\n");
                goto exit;
        }
        /* register ourselves with the security framework */
        if (register_security(&seclvl_ops)) {
                seclvl_printk(0, KERN_ERR,
                              "seclvl: Failure registering with the "
                              "kernel.\n");
                /* try registering with primary module */
                rc = mod_reg_security(MY_NAME, &seclvl_ops);
                if (rc) {
                        seclvl_printk(0, KERN_ERR, "seclvl: Failure "
                                      "registering with primary security "
                                      "module.\n");
                        seclvlfs_unregister();
                        goto exit;
                }               /* if primary module registered */
                secondary = 1;
        }                       /* if we registered ourselves with the security framework */

        seclvl_printk(0, KERN_INFO, "seclvl: Successfully initialized.\n");

        if (once) {
                once = 1;
                seclvl_printk(0, KERN_INFO, "seclvl is going away. It has been "
                                "buggy for ages. Also, be warned that "
                                "Securelevels are useless.");
        }
 exit:
        if (rc)
                printk(KERN_ERR "seclvl: Error during initialization: rc = "
                       "[%d]\n", rc);
        return rc;
}

/**
 * Remove the seclvl module.
 */
static void __exit seclvl_exit(void)
{
        seclvlfs_unregister();

        if (secondary)
                mod_unreg_security(MY_NAME, &seclvl_ops);
        else if (unregister_security(&seclvl_ops))
                seclvl_printk(0, KERN_INFO,
                              "seclvl: Failure unregistering with the "
                              "kernel\n");
}

module_init(seclvl_init);
module_exit(seclvl_exit);

MODULE_AUTHOR("Michael A. Halcrow <mike@halcrow.us>");
MODULE_DESCRIPTION("LSM implementation of the BSD Secure Levels");
MODULE_LICENSE("GPL");