1 files changed, 311 insertions, 0 deletions

diff --git a/modules/pam_usertype/pam_usertype.c b/modules/pam_usertype/pam_usertype.c
new file mode 100644
index 0000000..d03b73b
--- /dev/null
+++ b/modules/pam_usertype/pam_usertype.c
@@ -0,0 +1,311 @@
+/******************************************************************************
+ * Check user type based on login.defs.
+ *
+ * Copyright (c) 2020 Red Hat, Inc.
+ * Written by Pavel Březina <pbrezina@redhat.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, and the entire permission notice in its entirety,
+ *    including the disclaimer of warranties.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior
+ *    written permission.
+ *
+ * ALTERNATIVELY, this product may be distributed under the terms of
+ * the GNU Public License, in which case the provisions of the GPL are
+ * required INSTEAD OF the above restrictions.  (This clause is
+ * necessary due to a potential bad interaction between the GPL and
+ * the restrictions contained in a BSD-style copyright.)
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "config.h"
+
+#include <sys/types.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syslog.h>
+#include <unistd.h>
+#include <pwd.h>
+#include <ctype.h>
+#include <errno.h>
+
+#include <security/pam_modules.h>
+#include <security/pam_modutil.h>
+#include <security/pam_ext.h>
+
+#define LOGIN_DEFS "/etc/login.defs"
+
+enum pam_usertype_op {
+    OP_IS_SYSTEM,
+    OP_IS_REGULAR,
+
+    OP_SENTINEL
+};
+
+struct pam_usertype_opts {
+    enum pam_usertype_op op;
+    int use_uid;
+    int audit;
+};
+
+static int
+pam_usertype_parse_args(struct pam_usertype_opts *opts,
+                        pam_handle_t *pamh,
+                        int argc,
+                        const char **argv)
+{
+    int i;
+
+    memset(opts, 0, sizeof(struct pam_usertype_opts));
+    opts->op = OP_SENTINEL;
+
+    for (i = 0; i < argc; i++) {
+        if (strcmp(argv[i], "use_uid") == 0) {
+            opts->use_uid = 1;
+        } else if (strcmp(argv[i], "audit") == 0) {
+            opts->audit = 1;
+        } else if (strcmp(argv[i], "issystem") == 0) {
+            opts->op = OP_IS_SYSTEM;
+        } else if (strcmp(argv[i], "isregular") == 0) {
+            opts->op = OP_IS_REGULAR;
+        } else {
+            pam_syslog(pamh, LOG_WARNING, "Unknown argument: %s", argv[i]);
+            /* Just continue. */
+        }
+    }
+
+    if (opts->op == OP_SENTINEL) {
+        pam_syslog(pamh, LOG_ERR, "Operation not specified");
+        return PAM_SERVICE_ERR;
+    }
+
+    return PAM_SUCCESS;
+}
+
+static int
+pam_usertype_get_uid(struct pam_usertype_opts *opts,
+                     pam_handle_t *pamh,
+                     uid_t *_uid)
+{
+    struct passwd *pwd;
+    const char *username;
+    int ret;
+
+    /* Get uid of user that runs the application. */
+    if (opts->use_uid) {
+        pwd = pam_modutil_getpwuid(pamh, getuid());
+        if (pwd == NULL) {
+            pam_syslog(pamh, LOG_ERR,
+                       "error retrieving information about user %lu",
+                       (unsigned long)getuid());
+            return PAM_USER_UNKNOWN;
+        }
+
+        *_uid = pwd->pw_uid;
+        return PAM_SUCCESS;
+    }
+
+    /* Get uid of user that is being authenticated. */
+    ret = pam_get_user(pamh, &username, NULL);
+    if (ret != PAM_SUCCESS) {
+        pam_syslog(pamh, LOG_NOTICE, "cannot determine user name: %s",
+                   pam_strerror(pamh, ret));
+        return ret == PAM_CONV_AGAIN ? PAM_INCOMPLETE : ret;
+    }
+
+    pwd = pam_modutil_getpwnam(pamh, username);
+    if (pwd == NULL) {
+        if (opts->audit) {
+            pam_syslog(pamh, LOG_NOTICE,
+                       "error retrieving information about user %s", username);
+        }
+
+        pam_modutil_getpwnam(pamh, "root");
+
+        return PAM_USER_UNKNOWN;
+    }
+    pam_modutil_getpwnam(pamh, "pam_usertype_non_existent:");
+
+    *_uid = pwd->pw_uid;
+
+    return PAM_SUCCESS;
+}
+
+#define MAX_UID_VALUE 0xFFFFFFFFUL
+
+static uid_t
+pam_usertype_get_id(pam_handle_t *pamh,
+                    const char *key,
+                    uid_t default_value)
+{
+    unsigned long ul;
+    char *value;
+    char *ep;
+    uid_t uid;
+
+    value = pam_modutil_search_key(pamh, LOGIN_DEFS, key);
+    if (value == NULL) {
+        return default_value;
+    }
+
+    /* taken from get_lastlog_uid_max() */
+    ep = value + strlen(value);
+    while (ep > value && isspace(*(--ep))) {
+        *ep = '\0';
+    }
+
+    errno = 0;
+    ul = strtoul(value, &ep, 10);
+    if (!(ul >= MAX_UID_VALUE
+        || (uid_t)ul >= MAX_UID_VALUE
+        || (errno != 0 && ul == 0)
+        || value == ep
+        || *ep != '\0')) {
+        uid = (uid_t)ul;
+    } else {
+        uid = default_value;
+    }
+
+    free(value);
+
+    return uid;
+}
+
+static int
+pam_usertype_is_system(pam_handle_t *pamh, uid_t uid)
+{
+    uid_t uid_min;
+    uid_t sys_min;
+    uid_t sys_max;
+
+    if (uid == (uid_t)-1) {
+        pam_syslog(pamh, LOG_WARNING, "invalid uid");
+        return PAM_USER_UNKNOWN;
+    }
+
+    if (uid <= 99) {
+        /* Reserved. */
+        return PAM_SUCCESS;
+    }
+
+    if (uid == PAM_USERTYPE_OVERFLOW_UID) {
+        /* nobody */
+        return PAM_SUCCESS;
+    }
+
+    uid_min = pam_usertype_get_id(pamh, "UID_MIN", PAM_USERTYPE_UIDMIN);
+    sys_min = pam_usertype_get_id(pamh, "SYS_UID_MIN", PAM_USERTYPE_SYSUIDMIN);
+    sys_max = pam_usertype_get_id(pamh, "SYS_UID_MAX", uid_min - 1);
+
+    return uid >= sys_min && uid <= sys_max ? PAM_SUCCESS : PAM_AUTH_ERR;
+}
+
+static int
+pam_usertype_is_regular(pam_handle_t *pamh, uid_t uid)
+{
+    int ret;
+
+    ret = pam_usertype_is_system(pamh, uid);
+    switch (ret) {
+    case PAM_SUCCESS:
+        return PAM_AUTH_ERR;
+    case PAM_USER_UNKNOWN:
+        return PAM_USER_UNKNOWN;
+    default:
+        return PAM_SUCCESS;
+    }
+}
+
+static int
+pam_usertype_evaluate(struct pam_usertype_opts *opts,
+                      pam_handle_t *pamh,
+                      uid_t uid)
+{
+    switch (opts->op) {
+    case OP_IS_SYSTEM:
+        return pam_usertype_is_system(pamh, uid);
+    case OP_IS_REGULAR:
+        return pam_usertype_is_regular(pamh, uid);
+    default:
+        pam_syslog(pamh, LOG_ERR, "Unknown operation: %d", opts->op);
+        return PAM_SERVICE_ERR;
+    }
+}
+
+/**
+ * Arguments:
+ * - issystem: uid in <SYS_UID_MIN, SYS_UID_MAX>
+ * - isregular: not issystem
+ * - use_uid: use user that runs application not that is being authenticate (same as in pam_succeed_if)
+ * - audit: log unknown users to syslog
+ */
+int
+pam_sm_authenticate(pam_handle_t *pamh, int flags UNUSED,
+                    int argc, const char **argv)
+{
+    struct pam_usertype_opts opts;
+    uid_t uid = -1;
+    int ret;
+
+    ret = pam_usertype_parse_args(&opts, pamh, argc, argv);
+    if (ret != PAM_SUCCESS) {
+        return ret;
+    }
+
+    ret = pam_usertype_get_uid(&opts, pamh, &uid);
+    if (ret != PAM_SUCCESS) {
+        return ret;
+    }
+
+    return pam_usertype_evaluate(&opts, pamh, uid);
+}
+
+int
+pam_sm_setcred(pam_handle_t *pamh UNUSED, int flags UNUSED,
+               int argc UNUSED, const char **argv UNUSED)
+{
+	return PAM_IGNORE;
+}
+
+int
+pam_sm_acct_mgmt(pam_handle_t *pamh, int flags, int argc, const char **argv)
+{
+	return pam_sm_authenticate(pamh, flags, argc, argv);
+}
+
+int
+pam_sm_open_session(pam_handle_t *pamh, int flags, int argc, const char **argv)
+{
+	return pam_sm_authenticate(pamh, flags, argc, argv);
+}
+
+int
+pam_sm_close_session(pam_handle_t *pamh, int flags, int argc, const char **argv)
+{
+	return pam_sm_authenticate(pamh, flags, argc, argv);
+}
+
+int
+pam_sm_chauthtok(pam_handle_t *pamh, int flags, int argc, const char **argv)
+{
+	return pam_sm_authenticate(pamh, flags, argc, argv);
+}