diff options
Diffstat (limited to 'security/seclvl.c')
-rw-r--r-- | security/seclvl.c | 747 |
1 files changed, 747 insertions, 0 deletions
diff --git a/security/seclvl.c b/security/seclvl.c new file mode 100644 index 00000000000..8a0ab0d7949 --- /dev/null +++ b/security/seclvl.c @@ -0,0 +1,747 @@ +/** + * 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> + * + * 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/config.h> +#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/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) + +/** + * kobject stuff + */ + +struct subsystem seclvl_subsys; + +struct seclvl_obj { + char *name; + struct list_head slot_list; + struct kobject kobj; +}; + +/** + * There is a seclvl_attribute struct for each file in sysfs. + * + * In our case, we have one of these structs for "passwd" and another + * for "seclvl". + */ +struct seclvl_attribute { + struct attribute attr; + ssize_t(*show) (struct seclvl_obj *, char *); + ssize_t(*store) (struct seclvl_obj *, const char *, size_t); +}; + +/** + * When this function is called, one of the files in sysfs is being + * written to. attribute->store is a function pointer to whatever the + * struct seclvl_attribute store function pointer points to. It is + * unique for "passwd" and "seclvl". + */ +static ssize_t +seclvl_attr_store(struct kobject *kobj, + struct attribute *attr, const char *buf, size_t len) +{ + struct seclvl_obj *obj = container_of(kobj, struct seclvl_obj, kobj); + struct seclvl_attribute *attribute = + container_of(attr, struct seclvl_attribute, attr); + return (attribute->store ? attribute->store(obj, buf, len) : 0); +} + +static ssize_t +seclvl_attr_show(struct kobject *kobj, struct attribute *attr, char *buf) +{ + struct seclvl_obj *obj = container_of(kobj, struct seclvl_obj, kobj); + struct seclvl_attribute *attribute = + container_of(attr, struct seclvl_attribute, attr); + return (attribute->show ? attribute->show(obj, buf) : 0); +} + +/** + * Callback function pointers for show and store + */ +static struct sysfs_ops seclvlfs_sysfs_ops = { + .show = seclvl_attr_show, + .store = seclvl_attr_store, +}; + +static struct kobj_type seclvl_ktype = { + .sysfs_ops = &seclvlfs_sysfs_ops +}; + +decl_subsys(seclvl, &seclvl_ktype, NULL); + +/** + * 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; +} + +/** + * Called whenever the user reads the sysfs handle to this kernel + * object + */ +static ssize_t seclvl_read_file(struct seclvl_obj *obj, char *buff) +{ + return snprintf(buff, PAGE_SIZE, "%d\n", seclvl); +} + +/** + * 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 int do_seclvl_advance(int newlvl) +{ + if (newlvl <= seclvl) { + seclvl_printk(1, KERN_WARNING, "Cannot advance to seclvl " + "[%d]\n", newlvl); + return -EINVAL; + } + if (newlvl > 2) { + seclvl_printk(1, KERN_WARNING, "Cannot advance to seclvl " + "[%d]\n", newlvl); + return -EINVAL; + } + if (seclvl == -1) { + seclvl_printk(1, KERN_WARNING, "Not allowed to advance to " + "seclvl [%d]\n", seclvl); + return -EPERM; + } + seclvl = newlvl; + return 0; +} + +/** + * Called whenever the user writes to the sysfs handle to this kernel + * object (seclvl/seclvl). It expects a single-digit number. + */ +static ssize_t +seclvl_write_file(struct seclvl_obj *obj, const char *buff, size_t count) +{ + unsigned long val; + if (count > 2 || (count == 2 && buff[1] != '\n')) { + seclvl_printk(1, KERN_WARNING, "Invalid value passed to " + "seclvl: [%s]\n", buff); + return -EINVAL; + } + val = buff[0] - 48; + if (seclvl_sanity(val)) { + seclvl_printk(1, KERN_WARNING, "Illegal secure level " + "requested: [%d]\n", (int)val); + return -EPERM; + } + if (do_seclvl_advance(val)) { + seclvl_printk(0, KERN_ERR, "Failure advancing security level " + "to %lu\n", val); + } + return count; +} + +/* Generate sysfs_attr_seclvl */ +static struct seclvl_attribute sysfs_attr_seclvl = +__ATTR(seclvl, (S_IFREG | S_IRUGO | S_IWUSR), seclvl_read_file, + seclvl_write_file); + +static unsigned char hashedPassword[SHA1_DIGEST_SIZE]; + +/** + * Called whenever the user reads the sysfs passwd handle. + */ +static ssize_t seclvl_read_passwd(struct seclvl_obj *obj, char *buff) +{ + /* So just how good *is* your password? :-) */ + char tmp[3]; + int i = 0; + buff[0] = '\0'; + if (hideHash) { + /* Security through obscurity */ + return 0; + } + while (i < SHA1_DIGEST_SIZE) { + snprintf(tmp, 3, "%02x", hashedPassword[i]); + strncat(buff, tmp, 2); + i++; + } + strcat(buff, "\n"); + return ((SHA1_DIGEST_SIZE * 2) + 1); +} + +/** + * 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, int len) +{ + char *pgVirtAddr; + struct crypto_tfm *tfm; + struct scatterlist sg[1]; + 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 -ENOMEM; + } + tfm = crypto_alloc_tfm("sha1", 0); + if (tfm == NULL) { + seclvl_printk(0, KERN_ERR, + "Failed to load transform for SHA1\n"); + return -ENOSYS; + } + // Just get a new page; don't play around with page boundaries + // and scatterlists. + pgVirtAddr = (char *)__get_free_page(GFP_KERNEL); + sg[0].page = virt_to_page(pgVirtAddr); + sg[0].offset = 0; + sg[0].length = len; + strncpy(pgVirtAddr, plaintext, len); + crypto_digest_init(tfm); + crypto_digest_update(tfm, sg, 1); + crypto_digest_final(tfm, hash); + crypto_free_tfm(tfm); + free_page((unsigned long)pgVirtAddr); + 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 +seclvl_write_passwd(struct seclvl_obj *obj, const char *buff, size_t count) +{ + int i; + unsigned char tmp[SHA1_DIGEST_SIZE]; + int rc; + int len; + 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; + } + len = strlen(buff); + /* ``echo "secret" > seclvl/passwd'' includes a newline */ + if (buff[len - 1] == '\n') { + len--; + } + /* Hash the password, then compare the hashed values */ + if ((rc = plaintext_to_sha1(tmp, buff, len))) { + seclvl_printk(0, KERN_ERR, "Error hashing password: rc = " + "[%d]\n", rc); + return rc; + } + for (i = 0; i < SHA1_DIGEST_SIZE; i++) { + if (hashedPassword[i] != tmp[i]) { + return -EPERM; + } + } + seclvl_printk(0, KERN_INFO, + "Password accepted; seclvl reduced to 0.\n"); + seclvl = 0; + return count; +} + +/* Generate sysfs_attr_passwd */ +static struct seclvl_attribute sysfs_attr_passwd = +__ATTR(passwd, (S_IFREG | S_IRUGO | S_IWUSR), seclvl_read_passwd, + seclvl_write_passwd); + +/** + * Explicitely disallow ptrace'ing the init process. + */ +static int seclvl_ptrace(struct task_struct *parent, struct task_struct *child) +{ + if (seclvl >= 0) { + if (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) +{ + /* init can do anything it wants */ + if (tsk->pid == 1) + return 0; + + switch (seclvl) { + case 2: + /* fall through */ + case 1: + 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); + return -EPERM; + } else if (cap == CAP_SYS_RAWIO) { // Somewhat broad... + seclvl_printk(1, KERN_WARNING, "Attempt to perform " + "raw I/O while in secure level [%d] " + "denied\n", seclvl); + return -EPERM; + } 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); + return -EPERM; + } else if (cap == CAP_SETUID) { + seclvl_printk(1, KERN_WARNING, "Attempt to setuid " + "while in secure level [%d] denied\n", + seclvl); + return -EPERM; + } 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); + return -EPERM; + } + break; + default: + break; + } + /* from dummy.c */ + if (cap_is_fs_cap(cap) ? tsk->fsuid == 0 : tsk->euid == 0) + return 0; /* capability granted */ + seclvl_printk(1, KERN_WARNING, "Capability denied\n"); + return -EPERM; /* capability denied */ +} + +/** + * Disallow reversing the clock in seclvl > 1 + */ +static int seclvl_settime(struct timespec *tv, struct timezone *tz) +{ + struct timespec now; + if (seclvl > 1) { + 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; + struct inode *inode = NULL; + + if (dentry) { + inode = dentry->d_inode; + seclvl_bd_release(inode); + } +} + +/** + * Cannot unmount in secure level 2 + */ +static int seclvl_umount(struct vfsmount *mnt, int flags) +{ + if (current->pid == 1) { + return 0; + } + if (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; + hashedPassword[0] = '\0'; + if (*passwd) { + if (*sha1_passwd) { + seclvl_printk(0, KERN_ERR, "Error: Both " + "passwd and sha1_passwd " + "were set, but they are mutually " + "exclusive.\n"); + return -EINVAL; + } + if ((rc = plaintext_to_sha1(hashedPassword, passwd, + strlen(passwd)))) { + seclvl_printk(0, KERN_ERR, "Error: SHA1 support not " + "in kernel\n"); + return rc; + } + /* 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 0; +} + +/** + * Sysfs registrations + */ +static int doSysfsRegistrations(void) +{ + int rc = 0; + if ((rc = subsystem_register(&seclvl_subsys))) { + seclvl_printk(0, KERN_WARNING, + "Error [%d] registering seclvl subsystem\n", rc); + return rc; + } + sysfs_create_file(&seclvl_subsys.kset.kobj, &sysfs_attr_seclvl.attr); + if (*passwd || *sha1_passwd) { + sysfs_create_file(&seclvl_subsys.kset.kobj, + &sysfs_attr_passwd.attr); + } + return 0; +} + +/** + * Initialize the seclvl module. + */ +static int __init seclvl_init(void) +{ + int rc = 0; + 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; + } + sysfs_attr_seclvl.attr.owner = THIS_MODULE; + sysfs_attr_passwd.attr.owner = THIS_MODULE; + 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; + } + /* 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"); + goto exit; + } /* if primary module registered */ + secondary = 1; + } /* if we registered ourselves with the security framework */ + if ((rc = doSysfsRegistrations())) { + seclvl_printk(0, KERN_ERR, "Error registering with sysfs\n"); + goto exit; + } + seclvl_printk(0, KERN_INFO, "seclvl: Successfully initialized.\n"); + 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) +{ + sysfs_remove_file(&seclvl_subsys.kset.kobj, &sysfs_attr_seclvl.attr); + if (*passwd || *sha1_passwd) { + sysfs_remove_file(&seclvl_subsys.kset.kobj, + &sysfs_attr_passwd.attr); + } + subsystem_unregister(&seclvl_subsys); + if (secondary == 1) { + 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"); |