services.c

xen 3.2.2 源码

/*
 * Implementation of the security services.
 *
 * Authors : Stephen Smalley, <[e-mail]>
 *           James Morris <[e-mail]>
 *
 * Updated: Trusted Computer Solutions, Inc. <[e-mail]>
 *
 *    Support for enhanced MLS infrastructure.
 *
 * Updated: Frank Mayer <[e-mail]> and Karl MacMillan <[e-mail]>
 *
 *     Added conditional policy language extensions
 *
 * Copyright (C) 2004-2005 Trusted Computer Solutions, Inc.
 * Copyright (C) 2003 - 2004 Tresys Technology, LLC
 * Copyright (C) 2003 Red Hat, Inc., James Morris <[e-mail]>
 *    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.
 */

/* Ported to Xen 3.0, George Coker, <[e-mail]> */

#include <xen/lib.h>
#include <xen/xmalloc.h>
#include <xen/string.h>
#include <xen/spinlock.h>
#include <xen/errno.h>
#include "flask.h"
#include "avc.h"
#include "avc_ss.h"
#include "security.h"
#include "context.h"
#include "policydb.h"
#include "sidtab.h"
#include "services.h"
#include "conditional.h"
#include "mls.h"

unsigned int policydb_loaded_version;

static DEFINE_RWLOCK(policy_rwlock);
#define POLICY_RDLOCK read_lock(&policy_rwlock)
#define POLICY_WRLOCK write_lock_irq(&policy_rwlock)
#define POLICY_RDUNLOCK read_unlock(&policy_rwlock)
#define POLICY_WRUNLOCK write_unlock_irq(&policy_rwlock)

static DEFINE_SPINLOCK(load_sem);
#define LOAD_LOCK spin_lock(&load_sem)
#define LOAD_UNLOCK spin_unlock(&load_sem)

static struct sidtab sidtab;
struct policydb policydb;
int ss_initialized = 0;

/*
 * The largest sequence number that has been used when
 * providing an access decision to the access vector cache.
 * The sequence number only changes when a policy change
 * occurs.
 */
static u32 latest_granting = 0;

/* Forward declaration. */
static int context_struct_to_string(struct context *context, char **scontext,
                                                            u32 *scontext_len);

/*
 * Return the boolean value of a constraint expression
 * when it is applied to the specified source and target
 * security contexts.
 *
 * xcontext is a special beast...  It is used by the validatetrans rules
 * only.  For these rules, scontext is the context before the transition,
 * tcontext is the context after the transition, and xcontext is the context
 * of the process performing the transition.  All other callers of
 * constraint_expr_eval should pass in NULL for xcontext.
 */
static int constraint_expr_eval(struct context *scontext,
                            struct context *tcontext, struct context *xcontext, 
                                                struct constraint_expr *cexpr)
{
    u32 val1, val2;
    struct context *c;
    struct role_datum *r1, *r2;
    struct mls_level *l1, *l2;
    struct constraint_expr *e;
    int s[CEXPR_MAXDEPTH];
    int sp = -1;

    for ( e = cexpr; e; e = e->next )
    {
        switch ( e->expr_type )
        {
            case CEXPR_NOT:
                BUG_ON(sp < 0);
                s[sp] = !s[sp];
            break;
            case CEXPR_AND:
                BUG_ON(sp < 1);
                sp--;
                s[sp] &= s[sp+1];
            break;
            case CEXPR_OR:
                BUG_ON(sp < 1);
                sp--;
                s[sp] |= s[sp+1];
            break;
            case CEXPR_ATTR:
                if ( sp == (CEXPR_MAXDEPTH-1) )
                    return 0;
            switch ( e->attr )
            {
                case CEXPR_USER:
                    val1 = scontext->user;
                    val2 = tcontext->user;
                    break;
                case CEXPR_TYPE:
                    val1 = scontext->type;
                    val2 = tcontext->type;
                    break;
                case CEXPR_ROLE:
                    val1 = scontext->role;
                    val2 = tcontext->role;
                    r1 = policydb.role_val_to_struct[val1 - 1];
                    r2 = policydb.role_val_to_struct[val2 - 1];
                switch ( e->op )
                {
                    case CEXPR_DOM:
                        s[++sp] = ebitmap_get_bit(&r1->dominates, val2 - 1);
                    continue;
                    case CEXPR_DOMBY:
                        s[++sp] = ebitmap_get_bit(&r2->dominates, val1 - 1);
                    continue;
                    case CEXPR_INCOMP:
                        s[++sp] = ( !ebitmap_get_bit(&r1->dominates,
                                         val2 - 1) &&
                                !ebitmap_get_bit(&r2->dominates,
                                         val1 - 1) );
                    continue;
                    default:
                    break;
                }
                break;
                case CEXPR_L1L2:
                    l1 = &(scontext->range.level[0]);
                    l2 = &(tcontext->range.level[0]);
                    goto mls_ops;
                case CEXPR_L1H2:
                    l1 = &(scontext->range.level[0]);
                    l2 = &(tcontext->range.level[1]);
                    goto mls_ops;
                case CEXPR_H1L2:
                    l1 = &(scontext->range.level[1]);
                    l2 = &(tcontext->range.level[0]);
                    goto mls_ops;
                case CEXPR_H1H2:
                    l1 = &(scontext->range.level[1]);
                    l2 = &(tcontext->range.level[1]);
                    goto mls_ops;
                case CEXPR_L1H1:
                    l1 = &(scontext->range.level[0]);
                    l2 = &(scontext->range.level[1]);
                    goto mls_ops;
                case CEXPR_L2H2:
                    l1 = &(tcontext->range.level[0]);
                    l2 = &(tcontext->range.level[1]);
                    goto mls_ops;
mls_ops:
            switch ( e->op )
            {
                case CEXPR_EQ:
                    s[++sp] = mls_level_eq(l1, l2);
                continue;
                case CEXPR_NEQ:
                    s[++sp] = !mls_level_eq(l1, l2);
                continue;
                case CEXPR_DOM:
                    s[++sp] = mls_level_dom(l1, l2);
                continue;
                case CEXPR_DOMBY:
                    s[++sp] = mls_level_dom(l2, l1);
                continue;
                case CEXPR_INCOMP:
                    s[++sp] = mls_level_incomp(l2, l1);
                continue;
                default:
                    BUG();
                    return 0;
            }
            break;
            default:
                BUG();
                return 0;
            }

            switch ( e->op )
            {
                case CEXPR_EQ:
                    s[++sp] = (val1 == val2);
                break;
                case CEXPR_NEQ:
                    s[++sp] = (val1 != val2);
                break;
                default:
                    BUG();
                    return 0;
            }
            break;
            case CEXPR_NAMES:
                if ( sp == (CEXPR_MAXDEPTH-1) )
                    return 0;
                c = scontext;
                if ( e->attr & CEXPR_TARGET )
                    c = tcontext;
                else if ( e->attr & CEXPR_XTARGET )
                {
                    c = xcontext;
                    if ( !c )
                    {
                        BUG();
                        return 0;
                    }
                }
                if ( e->attr & CEXPR_USER )
                    val1 = c->user;
                else if ( e->attr & CEXPR_ROLE )
                    val1 = c->role;
                else if ( e->attr & CEXPR_TYPE )
                    val1 = c->type;
                else
                {
                    BUG();
                    return 0;
                }

            switch ( e->op )
            {
                case CEXPR_EQ:
                    s[++sp] = ebitmap_get_bit(&e->names, val1 - 1);
                break;
                case CEXPR_NEQ:
                    s[++sp] = !ebitmap_get_bit(&e->names, val1 - 1);
                break;
                default:
                    BUG();
                    return 0;
            }
            break;
            default:
                BUG();
                return 0;
        }
    }

    BUG_ON(sp != 0);
    return s[0];
}

/*
 * Compute access vectors based on a context structure pair for
 * the permissions in a particular class.
 */
static int context_struct_compute_av(struct context *scontext,
                            struct context *tcontext, u16 tclass, u32 requested, 
                                                        struct av_decision *avd)
{
    struct constraint_node *constraint;
    struct role_allow *ra;
    struct avtab_key avkey;
    struct avtab_node *node;
    struct class_datum *tclass_datum;
    struct ebitmap *sattr, *tattr;
    struct ebitmap_node *snode, *tnode;
    unsigned int i, j;

    if ( !tclass || tclass > policydb.p_classes.nprim )
    {
        printk(KERN_ERR "security_compute_av:  unrecognized class %d\n",
               tclass);
        return -EINVAL;
    }
    tclass_datum = policydb.class_val_to_struct[tclass - 1];

    /*
     * Initialize the access vectors to the default values.
     */
    avd->allowed = 0;
    avd->decided = 0xffffffff;
    avd->auditallow = 0;
    avd->auditdeny = 0xffffffff;
    avd->seqno = latest_granting;

    /*
     * If a specific type enforcement rule was defined for
     * this permission check, then use it.
     */
    avkey.target_class = tclass;
    avkey.specified = AVTAB_AV;
    sattr = &policydb.type_attr_map[scontext->type - 1];
    tattr = &policydb.type_attr_map[tcontext->type - 1];
    ebitmap_for_each_bit(sattr, snode, i)
    {
        if ( !ebitmap_node_get_bit(snode, i) )
            continue;
        ebitmap_for_each_bit(tattr, tnode, j)
        {
            if ( !ebitmap_node_get_bit(tnode, j) )
                continue;
            avkey.source_type = i + 1;
            avkey.target_type = j + 1;
            for ( node = avtab_search_node(&policydb.te_avtab, &avkey);
                 node != NULL;
                 node = avtab_search_node_next(node, avkey.specified) )
            {
                if ( node->key.specified == AVTAB_ALLOWED )
                    avd->allowed |= node->datum.data;
                else if ( node->key.specified == AVTAB_AUDITALLOW )
                    avd->auditallow |= node->datum.data;
                else if ( node->key.specified == AVTAB_AUDITDENY )
                    avd->auditdeny &= node->datum.data;
            }

            /* Check conditional av table for additional permissions */
            cond_compute_av(&policydb.te_cond_avtab, &avkey, avd);

        }
    }

    /*
     * Remove any permissions prohibited by a constraint (this includes
     * the MLS policy).
     */
    constraint = tclass_datum->constraints;
    while ( constraint )
    {
        if ( (constraint->permissions & (avd->allowed) ) &&
            !constraint_expr_eval(scontext, tcontext, NULL, constraint->expr))
        {
            avd->allowed = (avd->allowed) & ~(constraint->permissions);
        }
        constraint = constraint->next;
    }

    /*
     * If checking process transition permission and the
     * role is changing, then check the (current_role, new_role)
     * pair.
     */
    if ( tclass == SECCLASS_DOMAIN &&
/* removed until future dynamic domain capability
        (avd->allowed & (DOMAIN__TRANSITION | DOMAIN__DYNTRANSITION)) &&
*/
                                            scontext->role != tcontext->role )
        {
        for ( ra = policydb.role_allow; ra; ra = ra->next )
        {
            if ( scontext->role == ra->role && tcontext->role == ra->new_role )
                break;
        }
/* removed until future dynamic domain capability    
        if (!ra)
            avd->allowed = (avd->allowed) & ~(DOMAIN__TRANSITION |
                                            DOMAIN__DYNTRANSITION);
*/
    }

    return 0;
}

static int security_validtrans_handle_fail(struct context *ocontext,
                struct context *ncontext, struct context *tcontext, u16 tclass)
{
    char *o = NULL, *n = NULL, *t = NULL;
    u32 olen, nlen, tlen;

    if ( context_struct_to_string(ocontext, &o, &olen) < 0 )
        goto out;
    if ( context_struct_to_string(ncontext, &n, &nlen) < 0 )
        goto out;
    if ( context_struct_to_string(tcontext, &t, &tlen) < 0 )
        goto out;
    printk("security_validate_transition:  denied for"
              " oldcontext=%s newcontext=%s taskcontext=%s tclass=%s",
              o, n, t, policydb.p_class_val_to_name[tclass-1]);
out:
    xfree(o);
    xfree(n);
    xfree(t);

    if ( !flask_enforcing )
        return 0;
    return -EPERM;
}

int security_validate_transition(u32 oldsid, u32 newsid, u32 tasksid,
                                 u16 tclass)
{
    struct context *ocontext;
    struct context *ncontext;
    struct context *tcontext;
    struct class_datum *tclass_datum;
    struct constraint_node *constraint;
    int rc = 0;

    if ( !ss_initialized )
        return 0;

    POLICY_RDLOCK;

    if ( !tclass || tclass > policydb.p_classes.nprim )
    {
        printk(KERN_ERR "security_validate_transition: "
                                            "unrecognized class %d\n", tclass);
        rc = -EINVAL;
        goto out;
    }
    tclass_datum = policydb.class_val_to_struct[tclass - 1];

    ocontext = sidtab_search(&sidtab, oldsid);
    if ( !ocontext )
    {
        printk(KERN_ERR "security_validate_transition: "
               " unrecognized SID %d\n", oldsid);
        rc = -EINVAL;
        goto out;
    }

    ncontext = sidtab_search(&sidtab, newsid);
    if ( !ncontext )
    {
        printk(KERN_ERR "security_validate_transition: "
               " unrecognized SID %d\n", newsid);
        rc = -EINVAL;
        goto out;
    }

    tcontext = sidtab_search(&sidtab, tasksid);
    if ( !tcontext )
    {
        printk(KERN_ERR "security_validate_transition: "
               " unrecognized SID %d\n", tasksid);
        rc = -EINVAL;
        goto out;
    }

    constraint = tclass_datum->validatetrans;
    while ( constraint )
    {
        if ( !constraint_expr_eval(ocontext, ncontext, tcontext,
                                                            constraint->expr) )
        {
            rc = security_validtrans_handle_fail(ocontext, ncontext,
                                                 tcontext, tclass);
            goto out;
        }
        constraint = constraint->next;
    }

out:
    POLICY_RDUNLOCK;
    return rc;
}

/**
 * security_compute_av - Compute access vector decisions.
 * @ssid: source security identifier
 * @tsid: target security identifier
 * @tclass: target security class
 * @requested: requested permissions
 * @avd: access vector decisions
 *
 * Compute a set of access vector decisions based on the
 * SID pair (@ssid, @tsid) for the permissions in @tclass.
 * Return -%EINVAL if any of the parameters are invalid or %0
 * if the access vector decisions were computed successfully.
 */
int security_compute_av(u32 ssid, u32 tsid, u16 tclass, u32 requested,
                                                    struct av_decision *avd)
{
    struct context *scontext = NULL, *tcontext = NULL;
    int rc = 0;

    if ( !ss_initialized )
    {
        avd->allowed = 0xffffffff;
        avd->decided = 0xffffffff;
        avd->auditallow = 0;
        avd->auditdeny = 0xffffffff;
        avd->seqno = latest_granting;
        return 0;
    }

    POLICY_RDLOCK;

    scontext = sidtab_search(&sidtab, ssid);
    if ( !scontext )
    {
        printk("security_compute_av:  unrecognized SID %d\n", ssid);
        rc = -EINVAL;
        goto out;
    }
    tcontext = sidtab_search(&sidtab, tsid);
    if ( !tcontext )
    {
        printk("security_compute_av:  unrecognized SID %d\n", tsid);
        rc = -EINVAL;
        goto out;
    }

    rc = context_struct_compute_av(scontext, tcontext, tclass, requested, avd);
out:
    POLICY_RDUNLOCK;
    return rc;
}

/*
 * Write the security context string representation of
 * the context structure `context' into a dynamically
 * allocated string of the correct size.  Set `*scontext'
 * to point to this string and set `*scontext_len' to
 * the length of the string.
 */
static int context_struct_to_string(struct context *context, char **scontext, u32 *scontext_len)
{
    char *scontextp;

    *scontext = NULL;
    *scontext_len = 0;

    /* Compute the size of the context. */
    *scontext_len += strlen(policydb.p_user_val_to_name[context->user - 1]) + 1;
    *scontext_len += strlen(policydb.p_role_val_to_name[context->role - 1]) + 1;
    *scontext_len += strlen(policydb.p_type_val_to_name[context->type - 1]) + 1;
    *scontext_len += mls_compute_context_len(context);

    /* Allocate space for the context; caller must free this space. */
    scontextp = xmalloc_array(char, *scontext_len);
    if ( !scontextp )
        return -ENOMEM;

    *scontext = scontextp;

    /*
     * Copy the user name, role name and type name into the context.
     */
    snprintf(scontextp, *scontext_len, "%s:%s:%s",
        policydb.p_user_val_to_name[context->user - 1],
        policydb.p_role_val_to_name[context->role - 1],
        policydb.p_type_val_to_name[context->type - 1]);
    scontextp += strlen(policydb.p_user_val_to_name[context->user - 1]) +
                 1 + strlen(policydb.p_role_val_to_name[context->role - 1]) +