smack_access.c

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/*
 * Copyright (C) 2007 Casey Schaufler <[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.
 *
 * Author:
 *      Casey Schaufler <[email protected]>
 *
 */

#include <linux/types.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include "smack.h"

struct smack_known smack_known_huh = {
    .smk_known  = "?",
    .smk_secid  = 2,
};

struct smack_known smack_known_hat = {
    .smk_known  = "^",
    .smk_secid  = 3,
};

struct smack_known smack_known_star = {
    .smk_known  = "*",
    .smk_secid  = 4,
};

struct smack_known smack_known_floor = {
    .smk_known  = "_",
    .smk_secid  = 5,
};

struct smack_known smack_known_invalid = {
    .smk_known  = "",
    .smk_secid  = 6,
};

struct smack_known smack_known_web = {
    .smk_known  = "@",
    .smk_secid  = 7,
};

LIST_HEAD(smack_known_list);

/*
 * The initial value needs to be bigger than any of the
 * known values above.
 */
static u32 smack_next_secid = 10;

/*
 * what events do we log
 * can be overwritten at run-time by /smack/logging
 */
int log_policy = SMACK_AUDIT_DENIED;

int smk_access_entry(char *subject_label, char *object_label,
            struct list_head *rule_list)
{
    int may = -ENOENT;
    struct smack_rule *srp;

    list_for_each_entry_rcu(srp, rule_list, list) {
        if (srp->smk_object == object_label &&
            srp->smk_subject == subject_label) {
            may = srp->smk_access;
            break;
        }
    }

    return may;
}

int smk_access(char *subject_label, char *object_label, int request,
           struct smk_audit_info *a)
{
    struct smack_known *skp;
    int may = MAY_NOT;
    int rc = 0;

    /*
     * Hardcoded comparisons.
     *
     * A star subject can't access any object.
     */
    if (subject_label == smack_known_star.smk_known) {
        rc = -EACCES;
        goto out_audit;
    }
    /*
     * An internet object can be accessed by any subject.
     * Tasks cannot be assigned the internet label.
     * An internet subject can access any object.
     */
    if (object_label == smack_known_web.smk_known ||
        subject_label == smack_known_web.smk_known)
        goto out_audit;
    /*
     * A star object can be accessed by any subject.
     */
    if (object_label == smack_known_star.smk_known)
        goto out_audit;
    /*
     * An object can be accessed in any way by a subject
     * with the same label.
     */
    if (subject_label == object_label)
        goto out_audit;
    /*
     * A hat subject can read any object.
     * A floor object can be read by any subject.
     */
    if ((request & MAY_ANYREAD) == request) {
        if (object_label == smack_known_floor.smk_known)
            goto out_audit;
        if (subject_label == smack_known_hat.smk_known)
            goto out_audit;
    }
    /*
     * Beyond here an explicit relationship is required.
     * If the requested access is contained in the available
     * access (e.g. read is included in readwrite) it's
     * good. A negative response from smk_access_entry()
     * indicates there is no entry for this pair.
     */
    skp = smk_find_entry(subject_label);
    rcu_read_lock();
    may = smk_access_entry(subject_label, object_label, &skp->smk_rules);
    rcu_read_unlock();

    if (may > 0 && (request & may) == request)
        goto out_audit;

    rc = -EACCES;
out_audit:
#ifdef CONFIG_AUDIT
    if (a)
        smack_log(subject_label, object_label, request, rc, a);
#endif
    return rc;
}

int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
{
    struct task_smack *tsp = current_security();
    char *sp = smk_of_task(tsp);
    int may;
    int rc;

    /*
     * Check the global rule list
     */
    rc = smk_access(sp, obj_label, mode, NULL);
    if (rc == 0) {
        /*
         * If there is an entry in the task's rule list
         * it can further restrict access.
         */
        may = smk_access_entry(sp, obj_label, &tsp->smk_rules);
        if (may < 0)
            goto out_audit;
        if ((mode & may) == mode)
            goto out_audit;
        rc = -EACCES;
    }

    /*
     * Allow for priviliged to override policy.
     */
    if (rc != 0 && smack_privileged(CAP_MAC_OVERRIDE))
        rc = 0;

out_audit:
#ifdef CONFIG_AUDIT
    if (a)
        smack_log(sp, obj_label, mode, rc, a);
#endif
    return rc;
}

#ifdef CONFIG_AUDIT

static inline void smack_str_from_perm(char *string, int access)
{
    int i = 0;
    if (access & MAY_READ)
        string[i++] = 'r';
    if (access & MAY_WRITE)
        string[i++] = 'w';
    if (access & MAY_EXEC)
        string[i++] = 'x';
    if (access & MAY_APPEND)
        string[i++] = 'a';
    string[i] = '\0';
}
static void smack_log_callback(struct audit_buffer *ab, void *a)
{
    struct common_audit_data *ad = a;
    struct smack_audit_data *sad = ad->smack_audit_data;
    audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
             ad->smack_audit_data->function,
             sad->result ? "denied" : "granted");
    audit_log_format(ab, " subject=");
    audit_log_untrustedstring(ab, sad->subject);
    audit_log_format(ab, " object=");
    audit_log_untrustedstring(ab, sad->object);
    audit_log_format(ab, " requested=%s", sad->request);
}

void smack_log(char *subject_label, char *object_label, int request,
           int result, struct smk_audit_info *ad)
{
    char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
    struct smack_audit_data *sad;
    struct common_audit_data *a = &ad->a;

    /* check if we have to log the current event */
    if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
        return;
    if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
        return;

    sad = a->smack_audit_data;

    if (sad->function == NULL)
        sad->function = "unknown";

    /* end preparing the audit data */
    smack_str_from_perm(request_buffer, request);
    sad->subject = subject_label;
    sad->object  = object_label;
    sad->request = request_buffer;
    sad->result  = result;

    common_lsm_audit(a, smack_log_callback, NULL);
}
#else /* #ifdef CONFIG_AUDIT */
void smack_log(char *subject_label, char *object_label, int request,
               int result, struct smk_audit_info *ad)
{
}
#endif

DEFINE_MUTEX(smack_known_lock);

struct smack_known *smk_find_entry(const char *string)
{
    struct smack_known *skp;

    list_for_each_entry_rcu(skp, &smack_known_list, list) {
        if (strcmp(skp->smk_known, string) == 0)
            return skp;
    }

    return NULL;
}

char *smk_parse_smack(const char *string, int len)
{
    char *smack;
    int i;

    if (len <= 0)
        len = strlen(string) + 1;

    /*
     * Reserve a leading '-' as an indicator that
     * this isn't a label, but an option to interfaces
     * including /smack/cipso and /smack/cipso2
     */
    if (string[0] == '-')
        return NULL;

    for (i = 0; i < len; i++)
        if (string[i] > '~' || string[i] <= ' ' || string[i] == '/' ||
            string[i] == '"' || string[i] == '\\' || string[i] == '\'')
            break;

    if (i == 0 || i >= SMK_LONGLABEL)
        return NULL;

    smack = kzalloc(i + 1, GFP_KERNEL);
    if (smack != NULL) {
        strncpy(smack, string, i + 1);
        smack[i] = '\0';
    }
    return smack;
}

int smk_netlbl_mls(int level, char *catset, struct netlbl_lsm_secattr *sap,
            int len)
{
    unsigned char *cp;
    unsigned char m;
    int cat;
    int rc;
    int byte;

    sap->flags |= NETLBL_SECATTR_MLS_CAT;
    sap->attr.mls.lvl = level;
    sap->attr.mls.cat = netlbl_secattr_catmap_alloc(GFP_ATOMIC);
    sap->attr.mls.cat->startbit = 0;

    for (cat = 1, cp = catset, byte = 0; byte < len; cp++, byte++)
        for (m = 0x80; m != 0; m >>= 1, cat++) {
            if ((m & *cp) == 0)
                continue;
            rc = netlbl_secattr_catmap_setbit(sap->attr.mls.cat,
                              cat, GFP_ATOMIC);
            if (rc < 0) {
                netlbl_secattr_catmap_free(sap->attr.mls.cat);
                return rc;
            }
        }

    return 0;
}

struct smack_known *smk_import_entry(const char *string, int len)
{
    struct smack_known *skp;
    char *smack;
    int slen;
    int rc;

    smack = smk_parse_smack(string, len);
    if (smack == NULL)
        return NULL;

    mutex_lock(&smack_known_lock);

    skp = smk_find_entry(smack);
    if (skp != NULL)
        goto freeout;

    skp = kzalloc(sizeof(*skp), GFP_KERNEL);
    if (skp == NULL)
        goto freeout;

    skp->smk_known = smack;
    skp->smk_secid = smack_next_secid++;
    skp->smk_netlabel.domain = skp->smk_known;
    skp->smk_netlabel.flags =
        NETLBL_SECATTR_DOMAIN | NETLBL_SECATTR_MLS_LVL;
    /*
     * If direct labeling works use it.
     * Otherwise use mapped labeling.
     */
    slen = strlen(smack);
    if (slen < SMK_CIPSOLEN)
        rc = smk_netlbl_mls(smack_cipso_direct, skp->smk_known,
                   &skp->smk_netlabel, slen);
    else
        rc = smk_netlbl_mls(smack_cipso_mapped, (char *)&skp->smk_secid,
                   &skp->smk_netlabel, sizeof(skp->smk_secid));

    if (rc >= 0) {
        INIT_LIST_HEAD(&skp->smk_rules);
        mutex_init(&skp->smk_rules_lock);
        /*
         * Make sure that the entry is actually
         * filled before putting it on the list.
         */
        list_add_rcu(&skp->list, &smack_known_list);
        goto unlockout;
    }
    /*
     * smk_netlbl_mls failed.
     */
    kfree(skp);
    skp = NULL;
freeout:
    kfree(smack);
unlockout:
    mutex_unlock(&smack_known_lock);

    return skp;
}

char *smk_import(const char *string, int len)
{
    struct smack_known *skp;

    /* labels cannot begin with a '-' */
    if (string[0] == '-')
        return NULL;
    skp = smk_import_entry(string, len);
    if (skp == NULL)
        return NULL;
    return skp->smk_known;
}

char *smack_from_secid(const u32 secid)
{
    struct smack_known *skp;

    rcu_read_lock();
    list_for_each_entry_rcu(skp, &smack_known_list, list) {
        if (skp->smk_secid == secid) {
            rcu_read_unlock();
            return skp->smk_known;
        }
    }

    /*
     * If we got this far someone asked for the translation
     * of a secid that is not on the list.
     */
    rcu_read_unlock();
    return smack_known_invalid.smk_known;
}

u32 smack_to_secid(const char *smack)
{
    struct smack_known *skp = smk_find_entry(smack);

    if (skp == NULL)
        return 0;
    return skp->smk_secid;
}