/*
 * Copyright (C) 2016 Canonical Ltd
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "apparmor-support.h"
#include "string-utils.h"
#include "utils.h"

#include <errno.h>
#include <string.h>
#ifdef HAVE_APPARMOR
#include <sys/apparmor.h>
#endif  // ifdef HAVE_APPARMOR

#include "../libsnap-confine-private/cleanup-funcs.h"
#include "../libsnap-confine-private/utils.h"

// NOTE: Those constants map exactly what apparmor is returning and cannot be
// changed without breaking apparmor functionality.
#define SC_AA_ENFORCE_STR "enforce"
#define SC_AA_COMPLAIN_STR "complain"
#define SC_AA_MIXED_STR "mixed"
#define SC_AA_KILL_STR "kill"
#define SC_AA_UNCONFINED_STR "unconfined"

void sc_init_apparmor_support(struct sc_apparmor *apparmor) {
#ifdef HAVE_APPARMOR
    // Use aa_is_enabled() to see if apparmor is available in the kernel and
    // enabled at boot time. If it isn't log a diagnostic message and assume
    // we're not confined.
    if (aa_is_enabled() != true) {
        switch (errno) {
            case ENOSYS:
                debug("apparmor extensions to the system are not available");
                break;
            case ECANCELED:
                debug("apparmor is available on the system but has been disabled at boot");
                break;
            case EPERM:
                // NOTE: fall-through
            case EACCES:
                debug("insufficient permissions to determine if apparmor is enabled");
                // since snap-confine is setuid root this should
                // never happen so likely someone is trying to
                // manipulate our execution environment - fail hard

                // fall-through
            case ENOENT:
            case ENOMEM:
            default:
                // this shouldn't happen under normal usage so it
                // is possible someone is trying to manipulate our
                // execution environment - fail hard
                die("aa_is_enabled() failed unexpectedly (%s)", strerror(errno));
                break;
        }
        apparmor->is_confined = false;
        apparmor->mode = SC_AA_NOT_APPLICABLE;
        return;
    }
    // Use aa_getcon() to check the label of the current process and
    // confinement type. Note that the returned label must be released with
    // free() but the mode is a constant string that must not be freed.
    char *label SC_CLEANUP(sc_cleanup_string) = NULL;
    char *mode = NULL;
    if (aa_getcon(&label, &mode) < 0) {
        die("cannot query current apparmor profile");
    }
    debug("apparmor label on snap-confine is: %s", label);
    debug("apparmor mode is: %s", mode);
    // expect to be confined by a profile with the name of a valid
    // snap-confine binary since if not we may be executed under a
    // profile with more permissions than expected
    bool confined_mode = sc_streq(mode, SC_AA_ENFORCE_STR) || sc_streq(mode, SC_AA_KILL_STR);
    if (label != NULL && confined_mode && sc_is_expected_path(label)) {
        apparmor->is_confined = true;
    } else {
        apparmor->is_confined = false;
    }
    // There are several possible results for the confinement type (mode) that
    // are checked for below.
    if (mode != NULL && strcmp(mode, SC_AA_COMPLAIN_STR) == 0) {
        apparmor->mode = SC_AA_COMPLAIN;
    } else if (mode != NULL && strcmp(mode, SC_AA_ENFORCE_STR) == 0) {
        apparmor->mode = SC_AA_ENFORCE;
    } else if (mode != NULL && strcmp(mode, SC_AA_MIXED_STR) == 0) {
        apparmor->mode = SC_AA_MIXED;
    } else if (mode != NULL && strcmp(mode, SC_AA_KILL_STR) == 0) {
        apparmor->mode = SC_AA_KILL;
    } else {
        apparmor->mode = SC_AA_INVALID;
    }
#else
    apparmor->mode = SC_AA_NOT_APPLICABLE;
    apparmor->is_confined = false;
#endif  // ifdef HAVE_APPARMOR
}

void sc_maybe_aa_change_onexec(struct sc_apparmor *apparmor, const char *profile) {
#ifdef HAVE_APPARMOR
    if (apparmor->mode == SC_AA_NOT_APPLICABLE) {
        return;
    }
    debug("requesting changing of apparmor profile on next exec to %s", profile);
    if (aa_change_onexec(profile) < 0) {
        /* Save errno because secure_getenv() can overwrite it */
        int aa_change_onexec_errno = errno;
        if (secure_getenv("SNAPPY_LAUNCHER_INSIDE_TESTS") == NULL) {
            errno = aa_change_onexec_errno;
            if (errno == ENOENT) {
                fprintf(stderr,
                        "missing profile %s.\n"
                        "Please make sure that the snapd.apparmor service is enabled and started\n",
                        profile);
                exit(1);
            } else {
                die("cannot change profile for the next exec call");
            }
        }
    }
#endif  // ifdef HAVE_APPARMOR
}

void sc_maybe_aa_change_hat(struct sc_apparmor *apparmor, const char *subprofile, unsigned long magic_token) {
#ifdef HAVE_APPARMOR
    if (apparmor->mode == SC_AA_NOT_APPLICABLE) {
        return;
    }
    if (apparmor->is_confined) {
        debug("changing apparmor hat to %s", subprofile);
        if (aa_change_hat(subprofile, magic_token) < 0) {
            die("cannot change apparmor hat");
        }
    }
#endif  // ifdef HAVE_APPARMOR
}
