domain.c

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/*
 * AppArmor security module
 *
 * This file contains AppArmor policy attachment and domain transitions
 *
 * Copyright (C) 2002-2008 Novell/SUSE
 * Copyright 2009-2010 Canonical Ltd.
 *
 * 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.
 */

#include <linux/errno.h>
#include <linux/fdtable.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/syscalls.h>
#include <linux/tracehook.h>
#include <linux/personality.h>

#include "include/audit.h"
#include "include/apparmorfs.h"
#include "include/context.h"
#include "include/domain.h"
#include "include/file.h"
#include "include/ipc.h"
#include "include/match.h"
#include "include/path.h"
#include "include/policy.h"

void aa_free_domain_entries(struct aa_domain *domain)
{
    int i;
    if (domain) {
        if (!domain->table)
            return;

        for (i = 0; i < domain->size; i++)
            kzfree(domain->table[i]);
        kzfree(domain->table);
        domain->table = NULL;
    }
}

static int may_change_ptraced_domain(struct task_struct *task,
                     struct aa_profile *to_profile)
{
    struct task_struct *tracer;
    const struct cred *cred = NULL;
    struct aa_profile *tracerp = NULL;
    int error = 0;

    rcu_read_lock();
    tracer = ptrace_parent(task);
    if (tracer) {
        /* released below */
        cred = get_task_cred(tracer);
        tracerp = aa_cred_profile(cred);
    }

    /* not ptraced */
    if (!tracer || unconfined(tracerp))
        goto out;

    error = aa_may_ptrace(tracer, tracerp, to_profile, PTRACE_MODE_ATTACH);

out:
    rcu_read_unlock();
    if (cred)
        put_cred(cred);

    return error;
}

static struct file_perms change_profile_perms(struct aa_profile *profile,
                          struct aa_namespace *ns,
                          const char *name, u32 request,
                          unsigned int start)
{
    struct file_perms perms;
    struct path_cond cond = { };
    unsigned int state;

    if (unconfined(profile)) {
        perms.allow = AA_MAY_CHANGE_PROFILE | AA_MAY_ONEXEC;
        perms.audit = perms.quiet = perms.kill = 0;
        return perms;
    } else if (!profile->file.dfa) {
        return nullperms;
    } else if ((ns == profile->ns)) {
        /* try matching against rules with out namespace prepended */
        aa_str_perms(profile->file.dfa, start, name, &cond, &perms);
        if (COMBINED_PERM_MASK(perms) & request)
            return perms;
    }

    /* try matching with namespace name and then profile */
    state = aa_dfa_match(profile->file.dfa, start, ns->base.name);
    state = aa_dfa_match_len(profile->file.dfa, state, ":", 1);
    aa_str_perms(profile->file.dfa, state, name, &cond, &perms);

    return perms;
}

static struct aa_profile *__attach_match(const char *name,
                     struct list_head *head)
{
    int len = 0;
    struct aa_profile *profile, *candidate = NULL;

    list_for_each_entry(profile, head, base.list) {
        if (profile->flags & PFLAG_NULL)
            continue;
        if (profile->xmatch && profile->xmatch_len > len) {
            unsigned int state = aa_dfa_match(profile->xmatch,
                              DFA_START, name);
            u32 perm = dfa_user_allow(profile->xmatch, state);
            /* any accepting state means a valid match. */
            if (perm & MAY_EXEC) {
                candidate = profile;
                len = profile->xmatch_len;
            }
        } else if (!strcmp(profile->base.name, name))
            /* exact non-re match, no more searching required */
            return profile;
    }

    return candidate;
}

static struct aa_profile *find_attach(struct aa_namespace *ns,
                      struct list_head *list, const char *name)
{
    struct aa_profile *profile;

    read_lock(&ns->lock);
    profile = aa_get_profile(__attach_match(name, list));
    read_unlock(&ns->lock);

    return profile;
}

static const char *separate_fqname(const char *fqname, const char **ns_name)
{
    const char *name;

    if (fqname[0] == ':') {
        /* In this case there is guaranteed to be two \0 terminators
         * in the string.  They are verified at load time by
         * by unpack_trans_table
         */
        *ns_name = fqname + 1;      /* skip : */
        name = *ns_name + strlen(*ns_name) + 1;
        if (!*name)
            name = NULL;
    } else {
        *ns_name = NULL;
        name = fqname;
    }

    return name;
}

static const char *next_name(int xtype, const char *name)
{
    return NULL;
}

static struct aa_profile *x_table_lookup(struct aa_profile *profile, u32 xindex)
{
    struct aa_profile *new_profile = NULL;
    struct aa_namespace *ns = profile->ns;
    u32 xtype = xindex & AA_X_TYPE_MASK;
    int index = xindex & AA_X_INDEX_MASK;
    const char *name;

    /* index is guaranteed to be in range, validated at load time */
    for (name = profile->file.trans.table[index]; !new_profile && name;
         name = next_name(xtype, name)) {
        struct aa_namespace *new_ns;
        const char *xname = NULL;

        new_ns = NULL;
        if (xindex & AA_X_CHILD) {
            /* release by caller */
            new_profile = aa_find_child(profile, name);
            continue;
        } else if (*name == ':') {
            /* switching namespace */
            const char *ns_name;
            xname = name = separate_fqname(name, &ns_name);
            if (!xname)
                /* no name so use profile name */
                xname = profile->base.hname;
            if (*ns_name == '@') {
                /* TODO: variable support */
                ;
            }
            /* released below */
            new_ns = aa_find_namespace(ns, ns_name);
            if (!new_ns)
                continue;
        } else if (*name == '@') {
            /* TODO: variable support */
            continue;
        } else {
            /* basic namespace lookup */
            xname = name;
        }

        /* released by caller */
        new_profile = aa_lookup_profile(new_ns ? new_ns : ns, xname);
        aa_put_namespace(new_ns);
    }

    /* released by caller */
    return new_profile;
}

static struct aa_profile *x_to_profile(struct aa_profile *profile,
                       const char *name, u32 xindex)
{
    struct aa_profile *new_profile = NULL;
    struct aa_namespace *ns = profile->ns;
    u32 xtype = xindex & AA_X_TYPE_MASK;

    switch (xtype) {
    case AA_X_NONE:
        /* fail exec unless ix || ux fallback - handled by caller */
        return NULL;
    case AA_X_NAME:
        if (xindex & AA_X_CHILD)
            /* released by caller */
            new_profile = find_attach(ns, &profile->base.profiles,
                          name);
        else
            /* released by caller */
            new_profile = find_attach(ns, &ns->base.profiles,
                          name);
        break;
    case AA_X_TABLE:
        /* released by caller */
        new_profile = x_table_lookup(profile, xindex);
        break;
    }

    /* released by caller */
    return new_profile;
}

int apparmor_bprm_set_creds(struct linux_binprm *bprm)
{
    struct aa_task_cxt *cxt;
    struct aa_profile *profile, *new_profile = NULL;
    struct aa_namespace *ns;
    char *buffer = NULL;
    unsigned int state;
    struct file_perms perms = {};
    struct path_cond cond = {
        bprm->file->f_path.dentry->d_inode->i_uid,
        bprm->file->f_path.dentry->d_inode->i_mode
    };
    const char *name = NULL, *target = NULL, *info = NULL;
    int error = cap_bprm_set_creds(bprm);
    if (error)
        return error;

    if (bprm->cred_prepared)
        return 0;

    cxt = bprm->cred->security;
    BUG_ON(!cxt);

    profile = aa_get_profile(aa_newest_version(cxt->profile));
    /*
     * get the namespace from the replacement profile as replacement
     * can change the namespace
     */
    ns = profile->ns;
    state = profile->file.start;

    /* buffer freed below, name is pointer into buffer */
    error = aa_path_name(&bprm->file->f_path, profile->path_flags, &buffer,
                 &name, &info);
    if (error) {
        if (profile->flags &
            (PFLAG_IX_ON_NAME_ERROR | PFLAG_UNCONFINED))
            error = 0;
        name = bprm->filename;
        goto audit;
    }

    /* Test for onexec first as onexec directives override other
     * x transitions.
     */
    if (unconfined(profile)) {
        /* unconfined task */
        if (cxt->onexec)
            /* change_profile on exec already been granted */
            new_profile = aa_get_profile(cxt->onexec);
        else
            new_profile = find_attach(ns, &ns->base.profiles, name);
        if (!new_profile)
            goto cleanup;
        /*
         * NOTE: Domain transitions from unconfined are allowed
         * even when no_new_privs is set because this aways results
         * in a further reduction of permissions.
         */
        goto apply;
    }

    /* find exec permissions for name */
    state = aa_str_perms(profile->file.dfa, state, name, &cond, &perms);
    if (cxt->onexec) {
        struct file_perms cp;
        info = "change_profile onexec";
        if (!(perms.allow & AA_MAY_ONEXEC))
            goto audit;

        /* test if this exec can be paired with change_profile onexec.
         * onexec permission is linked to exec with a standard pairing
         * exec\0change_profile
         */
        state = aa_dfa_null_transition(profile->file.dfa, state);
        cp = change_profile_perms(profile, cxt->onexec->ns,
                      cxt->onexec->base.name,
                      AA_MAY_ONEXEC, state);

        if (!(cp.allow & AA_MAY_ONEXEC))
            goto audit;
        new_profile = aa_get_profile(aa_newest_version(cxt->onexec));
        goto apply;
    }

    if (perms.allow & MAY_EXEC) {
        /* exec permission determine how to transition */
        new_profile = x_to_profile(profile, name, perms.xindex);
        if (!new_profile) {
            if (perms.xindex & AA_X_INHERIT) {
                /* (p|c|n)ix - don't change profile but do
                 * use the newest version, which was picked
                 * up above when getting profile
                 */
                info = "ix fallback";
                new_profile = aa_get_profile(profile);
                goto x_clear;
            } else if (perms.xindex & AA_X_UNCONFINED) {
                new_profile = aa_get_profile(ns->unconfined);
                info = "ux fallback";
            } else {
                error = -ENOENT;
                info = "profile not found";
            }
        }
    } else if (COMPLAIN_MODE(profile)) {
        /* no exec permission - are we in learning mode */
        new_profile = aa_new_null_profile(profile, 0);
        if (!new_profile) {
            error = -ENOMEM;
            info = "could not create null profile";
        } else {
            error = -EACCES;
            target = new_profile->base.hname;
        }
        perms.xindex |= AA_X_UNSAFE;
    } else
        /* fail exec */
        error = -EACCES;

    /*
     * Policy has specified a domain transition, if no_new_privs then
     * fail the exec.
     */
    if (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) {
        aa_put_profile(new_profile);
        error = -EPERM;
        goto cleanup;
    }

    if (!new_profile)
        goto audit;

    if (bprm->unsafe & LSM_UNSAFE_SHARE) {
        /* FIXME: currently don't mediate shared state */
        ;
    }

    if (bprm->unsafe & (LSM_UNSAFE_PTRACE | LSM_UNSAFE_PTRACE_CAP)) {
        error = may_change_ptraced_domain(current, new_profile);
        if (error) {
            aa_put_profile(new_profile);
            goto audit;
        }
    }

    /* Determine if secure exec is needed.
     * Can be at this point for the following reasons:
     * 1. unconfined switching to confined
     * 2. confined switching to different confinement
     * 3. confined switching to unconfined
     *
     * Cases 2 and 3 are marked as requiring secure exec
     * (unless policy specified "unsafe exec")
     *
     * bprm->unsafe is used to cache the AA_X_UNSAFE permission
     * to avoid having to recompute in secureexec
     */
    if (!(perms.xindex & AA_X_UNSAFE)) {
        AA_DEBUG("scrubbing environment variables for %s profile=%s\n",
             name, new_profile->base.hname);
        bprm->unsafe |= AA_SECURE_X_NEEDED;
    }
apply:
    target = new_profile->base.hname;
    /* when transitioning profiles clear unsafe personality bits */
    bprm->per_clear |= PER_CLEAR_ON_SETID;

x_clear:
    aa_put_profile(cxt->profile);
    /* transfer new profile reference will be released when cxt is freed */
    cxt->profile = new_profile;

    /* clear out all temporary/transitional state from the context */
    aa_put_profile(cxt->previous);
    aa_put_profile(cxt->onexec);
    cxt->previous = NULL;
    cxt->onexec = NULL;
    cxt->token = 0;

audit:
    error = aa_audit_file(profile, &perms, GFP_KERNEL, OP_EXEC, MAY_EXEC,
                  name, target, cond.uid, info, error);

cleanup:
    aa_put_profile(profile);
    kfree(buffer);

    return error;
}

int apparmor_bprm_secureexec(struct linux_binprm *bprm)
{
    int ret = cap_bprm_secureexec(bprm);

    /* the decision to use secure exec is computed in set_creds
     * and stored in bprm->unsafe.
     */
    if (!ret && (bprm->unsafe & AA_SECURE_X_NEEDED))
        ret = 1;

    return ret;
}

void apparmor_bprm_committing_creds(struct linux_binprm *bprm)
{
    struct aa_profile *profile = __aa_current_profile();
    struct aa_task_cxt *new_cxt = bprm->cred->security;

    /* bail out if unconfined or not changing profile */
    if ((new_cxt->profile == profile) ||
        (unconfined(new_cxt->profile)))
        return;

    current->pdeath_signal = 0;

    /* reset soft limits and set hard limits for the new profile */
    __aa_transition_rlimits(profile, new_cxt->profile);
}

void apparmor_bprm_committed_creds(struct linux_binprm *bprm)
{
    /* TODO: cleanup signals - ipc mediation */
    return;
}

/*
 * Functions for self directed profile change
 */

static char *new_compound_name(const char *n1, const char *n2)
{
    char *name = kmalloc(strlen(n1) + strlen(n2) + 3, GFP_KERNEL);
    if (name)
        sprintf(name, "%s//%s", n1, n2);
    return name;
}

int aa_change_hat(const char *hats[], int count, u64 token, bool permtest)
{
    const struct cred *cred;
    struct aa_task_cxt *cxt;
    struct aa_profile *profile, *previous_profile, *hat = NULL;
    char *name = NULL;
    int i;
    struct file_perms perms = {};
    const char *target = NULL, *info = NULL;
    int error = 0;

    /*
     * Fail explicitly requested domain transitions if no_new_privs.
     * There is no exception for unconfined as change_hat is not
     * available.
     */
    if (current->no_new_privs)
        return -EPERM;

    /* released below */
    cred = get_current_cred();
    cxt = cred->security;
    profile = aa_cred_profile(cred);
    previous_profile = cxt->previous;

    if (unconfined(profile)) {
        info = "unconfined";
        error = -EPERM;
        goto audit;
    }

    if (count) {
        /* attempting to change into a new hat or switch to a sibling */
        struct aa_profile *root;
        root = PROFILE_IS_HAT(profile) ? profile->parent : profile;

        /* find first matching hat */
        for (i = 0; i < count && !hat; i++)
            /* released below */
            hat = aa_find_child(root, hats[i]);
        if (!hat) {
            if (!COMPLAIN_MODE(root) || permtest) {
                if (list_empty(&root->base.profiles))
                    error = -ECHILD;
                else
                    error = -ENOENT;
                goto out;
            }

            /*
             * In complain mode and failed to match any hats.
             * Audit the failure is based off of the first hat
             * supplied.  This is done due how userspace
             * interacts with change_hat.
             *
             * TODO: Add logging of all failed hats
             */

            /* freed below */
            name = new_compound_name(root->base.hname, hats[0]);
            target = name;
            /* released below */
            hat = aa_new_null_profile(profile, 1);
            if (!hat) {
                info = "failed null profile create";
                error = -ENOMEM;
                goto audit;
            }
        } else {
            target = hat->base.hname;
            if (!PROFILE_IS_HAT(hat)) {
                info = "target not hat";
                error = -EPERM;
                goto audit;
            }
        }

        error = may_change_ptraced_domain(current, hat);
        if (error) {
            info = "ptraced";
            error = -EPERM;
            goto audit;
        }

        if (!permtest) {
            error = aa_set_current_hat(hat, token);
            if (error == -EACCES)
                /* kill task in case of brute force attacks */
                perms.kill = AA_MAY_CHANGEHAT;
            else if (name && !error)
                /* reset error for learning of new hats */
                error = -ENOENT;
        }
    } else if (previous_profile) {
        /* Return to saved profile.  Kill task if restore fails
         * to avoid brute force attacks
         */
        target = previous_profile->base.hname;
        error = aa_restore_previous_profile(token);
        perms.kill = AA_MAY_CHANGEHAT;
    } else
        /* ignore restores when there is no saved profile */
        goto out;

audit:
    if (!permtest)
        error = aa_audit_file(profile, &perms, GFP_KERNEL,
                      OP_CHANGE_HAT, AA_MAY_CHANGEHAT, NULL,
                      target, GLOBAL_ROOT_UID, info, error);

out:
    aa_put_profile(hat);
    kfree(name);
    put_cred(cred);

    return error;
}

int aa_change_profile(const char *ns_name, const char *hname, bool onexec,
              bool permtest)
{
    const struct cred *cred;
    struct aa_task_cxt *cxt;
    struct aa_profile *profile, *target = NULL;
    struct aa_namespace *ns = NULL;
    struct file_perms perms = {};
    const char *name = NULL, *info = NULL;
    int op, error = 0;
    u32 request;

    if (!hname && !ns_name)
        return -EINVAL;

    if (onexec) {
        request = AA_MAY_ONEXEC;
        op = OP_CHANGE_ONEXEC;
    } else {
        request = AA_MAY_CHANGE_PROFILE;
        op = OP_CHANGE_PROFILE;
    }

    cred = get_current_cred();
    cxt = cred->security;
    profile = aa_cred_profile(cred);

    /*
     * Fail explicitly requested domain transitions if no_new_privs
     * and not unconfined.
     * Domain transitions from unconfined are allowed even when
     * no_new_privs is set because this aways results in a reduction
     * of permissions.
     */
    if (current->no_new_privs && !unconfined(profile)) {
        put_cred(cred);
        return -EPERM;
    }

    if (ns_name) {
        /* released below */
        ns = aa_find_namespace(profile->ns, ns_name);
        if (!ns) {
            /* we don't create new namespace in complain mode */
            name = ns_name;
            info = "namespace not found";
            error = -ENOENT;
            goto audit;
        }
    } else
        /* released below */
        ns = aa_get_namespace(profile->ns);

    /* if the name was not specified, use the name of the current profile */
    if (!hname) {
        if (unconfined(profile))
            hname = ns->unconfined->base.hname;
        else
            hname = profile->base.hname;
    }

    perms = change_profile_perms(profile, ns, hname, request,
                     profile->file.start);
    if (!(perms.allow & request)) {
        error = -EACCES;
        goto audit;
    }

    /* released below */
    target = aa_lookup_profile(ns, hname);
    if (!target) {
        info = "profile not found";
        error = -ENOENT;
        if (permtest || !COMPLAIN_MODE(profile))
            goto audit;
        /* released below */
        target = aa_new_null_profile(profile, 0);
        if (!target) {
            info = "failed null profile create";
            error = -ENOMEM;
            goto audit;
        }
    }

    /* check if tracing task is allowed to trace target domain */
    error = may_change_ptraced_domain(current, target);
    if (error) {
        info = "ptrace prevents transition";
        goto audit;
    }

    if (permtest)
        goto audit;

    if (onexec)
        error = aa_set_current_onexec(target);
    else
        error = aa_replace_current_profile(target);

audit:
    if (!permtest)
        error = aa_audit_file(profile, &perms, GFP_KERNEL, op, request,
                      name, hname, GLOBAL_ROOT_UID, info, error);

    aa_put_namespace(ns);
    aa_put_profile(target);
    put_cred(cred);

    return error;
}