ima_policy.c

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/*
 * Copyright (C) 2008 IBM Corporation
 * Author: Mimi Zohar <[email protected]>
 *
 * 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, version 2 of the License.
 *
 * ima_policy.c
 *  - initialize default measure policy rules
 *
 */
#include <linux/module.h>
#include <linux/list.h>
#include <linux/security.h>
#include <linux/magic.h>
#include <linux/parser.h>
#include <linux/slab.h>

#include "ima.h"

/* flags definitions */
#define IMA_FUNC    0x0001
#define IMA_MASK    0x0002
#define IMA_FSMAGIC 0x0004
#define IMA_UID     0x0008
#define IMA_FOWNER  0x0010

#define UNKNOWN     0
#define MEASURE     0x0001  /* same as IMA_MEASURE */
#define DONT_MEASURE    0x0002
#define APPRAISE    0x0004  /* same as IMA_APPRAISE */
#define DONT_APPRAISE   0x0008
#define AUDIT       0x0040

#define MAX_LSM_RULES 6
enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
    LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE
};

struct ima_rule_entry {
    struct list_head list;
    int action;
    unsigned int flags;
    enum ima_hooks func;
    int mask;
    unsigned long fsmagic;
    kuid_t uid;
    kuid_t fowner;
    struct {
        void *rule; /* LSM file metadata specific */
        int type;   /* audit type */
    } lsm[MAX_LSM_RULES];
};

/*
 * Without LSM specific knowledge, the default policy can only be
 * written in terms of .action, .func, .mask, .fsmagic, .uid, and .fowner
 */

/*
 * The minimum rule set to allow for full TCB coverage.  Measures all files
 * opened or mmap for exec and everything read by root.  Dangerous because
 * normal users can easily run the machine out of memory simply building
 * and running executables.
 */
static struct ima_rule_entry default_rules[] = {
    {.action = DONT_MEASURE,.fsmagic = PROC_SUPER_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_MEASURE,.fsmagic = SYSFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_MEASURE,.fsmagic = DEBUGFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_MEASURE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_MEASURE,.fsmagic = RAMFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_MEASURE,.fsmagic = DEVPTS_SUPER_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_MEASURE,.fsmagic = BINFMTFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC},
    {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC,
     .flags = IMA_FUNC | IMA_MASK},
    {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC,
     .flags = IMA_FUNC | IMA_MASK},
    {.action = MEASURE,.func = FILE_CHECK,.mask = MAY_READ,.uid = GLOBAL_ROOT_UID,
     .flags = IMA_FUNC | IMA_MASK | IMA_UID},
};

static struct ima_rule_entry default_appraise_rules[] = {
    {.action = DONT_APPRAISE,.fsmagic = PROC_SUPER_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_APPRAISE,.fsmagic = SYSFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_APPRAISE,.fsmagic = DEBUGFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_APPRAISE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_APPRAISE,.fsmagic = RAMFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_APPRAISE,.fsmagic = DEVPTS_SUPER_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_APPRAISE,.fsmagic = BINFMTFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_APPRAISE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_APPRAISE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC},
    {.action = DONT_APPRAISE,.fsmagic = CGROUP_SUPER_MAGIC,.flags = IMA_FSMAGIC},
    {.action = APPRAISE,.fowner = GLOBAL_ROOT_UID,.flags = IMA_FOWNER},
};

static LIST_HEAD(ima_default_rules);
static LIST_HEAD(ima_policy_rules);
static struct list_head *ima_rules;

static DEFINE_MUTEX(ima_rules_mutex);

static bool ima_use_tcb __initdata;
static int __init default_measure_policy_setup(char *str)
{
    ima_use_tcb = 1;
    return 1;
}
__setup("ima_tcb", default_measure_policy_setup);

static bool ima_use_appraise_tcb __initdata;
static int __init default_appraise_policy_setup(char *str)
{
    ima_use_appraise_tcb = 1;
    return 1;
}
__setup("ima_appraise_tcb", default_appraise_policy_setup);

static bool ima_match_rules(struct ima_rule_entry *rule,
                struct inode *inode, enum ima_hooks func, int mask)
{
    struct task_struct *tsk = current;
    const struct cred *cred = current_cred();
    int i;

    if ((rule->flags & IMA_FUNC) && rule->func != func)
        return false;
    if ((rule->flags & IMA_MASK) && rule->mask != mask)
        return false;
    if ((rule->flags & IMA_FSMAGIC)
        && rule->fsmagic != inode->i_sb->s_magic)
        return false;
    if ((rule->flags & IMA_UID) && !uid_eq(rule->uid, cred->uid))
        return false;
    if ((rule->flags & IMA_FOWNER) && !uid_eq(rule->fowner, inode->i_uid))
        return false;
    for (i = 0; i < MAX_LSM_RULES; i++) {
        int rc = 0;
        u32 osid, sid;

        if (!rule->lsm[i].rule)
            continue;

        switch (i) {
        case LSM_OBJ_USER:
        case LSM_OBJ_ROLE:
        case LSM_OBJ_TYPE:
            security_inode_getsecid(inode, &osid);
            rc = security_filter_rule_match(osid,
                            rule->lsm[i].type,
                            Audit_equal,
                            rule->lsm[i].rule,
                            NULL);
            break;
        case LSM_SUBJ_USER:
        case LSM_SUBJ_ROLE:
        case LSM_SUBJ_TYPE:
            security_task_getsecid(tsk, &sid);
            rc = security_filter_rule_match(sid,
                            rule->lsm[i].type,
                            Audit_equal,
                            rule->lsm[i].rule,
                            NULL);
        default:
            break;
        }
        if (!rc)
            return false;
    }
    return true;
}

int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask,
             int flags)
{
    struct ima_rule_entry *entry;
    int action = 0, actmask = flags | (flags << 1);

    list_for_each_entry(entry, ima_rules, list) {

        if (!(entry->action & actmask))
            continue;

        if (!ima_match_rules(entry, inode, func, mask))
            continue;

        action |= entry->action & IMA_DO_MASK;
        if (entry->action & IMA_DO_MASK)
            actmask &= ~(entry->action | entry->action << 1);
        else
            actmask &= ~(entry->action | entry->action >> 1);

        if (!actmask)
            break;
    }

    return action;
}

void __init ima_init_policy(void)
{
    int i, measure_entries, appraise_entries;

    /* if !ima_use_tcb set entries = 0 so we load NO default rules */
    measure_entries = ima_use_tcb ? ARRAY_SIZE(default_rules) : 0;
    appraise_entries = ima_use_appraise_tcb ?
             ARRAY_SIZE(default_appraise_rules) : 0;
    
    for (i = 0; i < measure_entries + appraise_entries; i++) {
        if (i < measure_entries)
            list_add_tail(&default_rules[i].list,
                      &ima_default_rules);
        else {
            int j = i - measure_entries;

            list_add_tail(&default_appraise_rules[j].list,
                      &ima_default_rules);
        }
    }

    ima_rules = &ima_default_rules;
}

void ima_update_policy(void)
{
    const char *op = "policy_update";
    const char *cause = "already exists";
    int result = 1;
    int audit_info = 0;

    if (ima_rules == &ima_default_rules) {
        ima_rules = &ima_policy_rules;
        cause = "complete";
        result = 0;
    }
    integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
                NULL, op, cause, result, audit_info);
}

enum {
    Opt_err = -1,
    Opt_measure = 1, Opt_dont_measure,
    Opt_appraise, Opt_dont_appraise,
    Opt_audit,
    Opt_obj_user, Opt_obj_role, Opt_obj_type,
    Opt_subj_user, Opt_subj_role, Opt_subj_type,
    Opt_func, Opt_mask, Opt_fsmagic, Opt_uid, Opt_fowner
};

static match_table_t policy_tokens = {
    {Opt_measure, "measure"},
    {Opt_dont_measure, "dont_measure"},
    {Opt_appraise, "appraise"},
    {Opt_dont_appraise, "dont_appraise"},
    {Opt_audit, "audit"},
    {Opt_obj_user, "obj_user=%s"},
    {Opt_obj_role, "obj_role=%s"},
    {Opt_obj_type, "obj_type=%s"},
    {Opt_subj_user, "subj_user=%s"},
    {Opt_subj_role, "subj_role=%s"},
    {Opt_subj_type, "subj_type=%s"},
    {Opt_func, "func=%s"},
    {Opt_mask, "mask=%s"},
    {Opt_fsmagic, "fsmagic=%s"},
    {Opt_uid, "uid=%s"},
    {Opt_fowner, "fowner=%s"},
    {Opt_err, NULL}
};

static int ima_lsm_rule_init(struct ima_rule_entry *entry,
                 char *args, int lsm_rule, int audit_type)
{
    int result;

    if (entry->lsm[lsm_rule].rule)
        return -EINVAL;

    entry->lsm[lsm_rule].type = audit_type;
    result = security_filter_rule_init(entry->lsm[lsm_rule].type,
                       Audit_equal, args,
                       &entry->lsm[lsm_rule].rule);
    if (!entry->lsm[lsm_rule].rule)
        return -EINVAL;
    return result;
}

static void ima_log_string(struct audit_buffer *ab, char *key, char *value)
{
    audit_log_format(ab, "%s=", key);
    audit_log_untrustedstring(ab, value);
    audit_log_format(ab, " ");
}

static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
{
    struct audit_buffer *ab;
    char *p;
    int result = 0;

    ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE);

    entry->uid = INVALID_UID;
    entry->fowner = INVALID_UID;
    entry->action = UNKNOWN;
    while ((p = strsep(&rule, " \t")) != NULL) {
        substring_t args[MAX_OPT_ARGS];
        int token;
        unsigned long lnum;

        if (result < 0)
            break;
        if ((*p == '\0') || (*p == ' ') || (*p == '\t'))
            continue;
        token = match_token(p, policy_tokens, args);
        switch (token) {
        case Opt_measure:
            ima_log_string(ab, "action", "measure");

            if (entry->action != UNKNOWN)
                result = -EINVAL;

            entry->action = MEASURE;
            break;
        case Opt_dont_measure:
            ima_log_string(ab, "action", "dont_measure");

            if (entry->action != UNKNOWN)
                result = -EINVAL;

            entry->action = DONT_MEASURE;
            break;
        case Opt_appraise:
            ima_log_string(ab, "action", "appraise");

            if (entry->action != UNKNOWN)
                result = -EINVAL;

            entry->action = APPRAISE;
            break;
        case Opt_dont_appraise:
            ima_log_string(ab, "action", "dont_appraise");

            if (entry->action != UNKNOWN)
                result = -EINVAL;

            entry->action = DONT_APPRAISE;
            break;
        case Opt_audit:
            ima_log_string(ab, "action", "audit");

            if (entry->action != UNKNOWN)
                result = -EINVAL;

            entry->action = AUDIT;
            break;
        case Opt_func:
            ima_log_string(ab, "func", args[0].from);

            if (entry->func)
                result = -EINVAL;

            if (strcmp(args[0].from, "FILE_CHECK") == 0)
                entry->func = FILE_CHECK;
            /* PATH_CHECK is for backwards compat */
            else if (strcmp(args[0].from, "PATH_CHECK") == 0)
                entry->func = FILE_CHECK;
            else if (strcmp(args[0].from, "FILE_MMAP") == 0)
                entry->func = FILE_MMAP;
            else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
                entry->func = BPRM_CHECK;
            else
                result = -EINVAL;
            if (!result)
                entry->flags |= IMA_FUNC;
            break;
        case Opt_mask:
            ima_log_string(ab, "mask", args[0].from);

            if (entry->mask)
                result = -EINVAL;

            if ((strcmp(args[0].from, "MAY_EXEC")) == 0)
                entry->mask = MAY_EXEC;
            else if (strcmp(args[0].from, "MAY_WRITE") == 0)
                entry->mask = MAY_WRITE;
            else if (strcmp(args[0].from, "MAY_READ") == 0)
                entry->mask = MAY_READ;
            else if (strcmp(args[0].from, "MAY_APPEND") == 0)
                entry->mask = MAY_APPEND;
            else
                result = -EINVAL;
            if (!result)
                entry->flags |= IMA_MASK;
            break;
        case Opt_fsmagic:
            ima_log_string(ab, "fsmagic", args[0].from);

            if (entry->fsmagic) {
                result = -EINVAL;
                break;
            }

            result = strict_strtoul(args[0].from, 16,
                        &entry->fsmagic);
            if (!result)
                entry->flags |= IMA_FSMAGIC;
            break;
        case Opt_uid:
            ima_log_string(ab, "uid", args[0].from);

            if (uid_valid(entry->uid)) {
                result = -EINVAL;
                break;
            }

            result = strict_strtoul(args[0].from, 10, &lnum);
            if (!result) {
                entry->uid = make_kuid(current_user_ns(), (uid_t)lnum);
                if (!uid_valid(entry->uid) || (((uid_t)lnum) != lnum))
                    result = -EINVAL;
                else
                    entry->flags |= IMA_UID;
            }
            break;
        case Opt_fowner:
            ima_log_string(ab, "fowner", args[0].from);

            if (uid_valid(entry->fowner)) {
                result = -EINVAL;
                break;
            }

            result = strict_strtoul(args[0].from, 10, &lnum);
            if (!result) {
                entry->fowner = make_kuid(current_user_ns(), (uid_t)lnum);
                if (!uid_valid(entry->fowner) || (((uid_t)lnum) != lnum))
                    result = -EINVAL;
                else
                    entry->flags |= IMA_FOWNER;
            }
            break;
        case Opt_obj_user:
            ima_log_string(ab, "obj_user", args[0].from);
            result = ima_lsm_rule_init(entry, args[0].from,
                           LSM_OBJ_USER,
                           AUDIT_OBJ_USER);
            break;
        case Opt_obj_role:
            ima_log_string(ab, "obj_role", args[0].from);
            result = ima_lsm_rule_init(entry, args[0].from,
                           LSM_OBJ_ROLE,
                           AUDIT_OBJ_ROLE);
            break;
        case Opt_obj_type:
            ima_log_string(ab, "obj_type", args[0].from);
            result = ima_lsm_rule_init(entry, args[0].from,
                           LSM_OBJ_TYPE,
                           AUDIT_OBJ_TYPE);
            break;
        case Opt_subj_user:
            ima_log_string(ab, "subj_user", args[0].from);
            result = ima_lsm_rule_init(entry, args[0].from,
                           LSM_SUBJ_USER,
                           AUDIT_SUBJ_USER);
            break;
        case Opt_subj_role:
            ima_log_string(ab, "subj_role", args[0].from);
            result = ima_lsm_rule_init(entry, args[0].from,
                           LSM_SUBJ_ROLE,
                           AUDIT_SUBJ_ROLE);
            break;
        case Opt_subj_type:
            ima_log_string(ab, "subj_type", args[0].from);
            result = ima_lsm_rule_init(entry, args[0].from,
                           LSM_SUBJ_TYPE,
                           AUDIT_SUBJ_TYPE);
            break;
        case Opt_err:
            ima_log_string(ab, "UNKNOWN", p);
            result = -EINVAL;
            break;
        }
    }
    if (!result && (entry->action == UNKNOWN))
        result = -EINVAL;

    audit_log_format(ab, "res=%d", !result);
    audit_log_end(ab);
    return result;
}

ssize_t ima_parse_add_rule(char *rule)
{
    const char *op = "update_policy";
    char *p;
    struct ima_rule_entry *entry;
    ssize_t result, len;
    int audit_info = 0;

    /* Prevent installed policy from changing */
    if (ima_rules != &ima_default_rules) {
        integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
                    NULL, op, "already exists",
                    -EACCES, audit_info);
        return -EACCES;
    }

    entry = kzalloc(sizeof(*entry), GFP_KERNEL);
    if (!entry) {
        integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
                    NULL, op, "-ENOMEM", -ENOMEM, audit_info);
        return -ENOMEM;
    }

    INIT_LIST_HEAD(&entry->list);

    p = strsep(&rule, "\n");
    len = strlen(p) + 1;

    if (*p == '#') {
        kfree(entry);
        return len;
    }

    result = ima_parse_rule(p, entry);
    if (result) {
        kfree(entry);
        integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
                    NULL, op, "invalid policy", result,
                    audit_info);
        return result;
    }

    mutex_lock(&ima_rules_mutex);
    list_add_tail(&entry->list, &ima_policy_rules);
    mutex_unlock(&ima_rules_mutex);

    return len;
}

/* ima_delete_rules called to cleanup invalid policy */
void ima_delete_rules(void)
{
    struct ima_rule_entry *entry, *tmp;

    mutex_lock(&ima_rules_mutex);
    list_for_each_entry_safe(entry, tmp, &ima_policy_rules, list) {
        list_del(&entry->list);
        kfree(entry);
    }
    mutex_unlock(&ima_rules_mutex);
}