LibCore: Add Core::Account for login management.

Core::Account abstracts login semantics like password checking and
switching uid/gid.

Libraries/LibCore/Account.cpp

@@ -0,0 +1,207 @@
+/*
+ * Copyright (c) 2020, Peter Elliott <pelliott@ualberta.ca>
+ * All rights reserved.
+ *
+ * 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, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT HOLDER OR CONTRIBUTORS 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 <AK/Base64.h>
+#include <AK/Random.h>
+#include <LibCore/Account.h>
+#include <LibCore/File.h>
+#include <grp.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+namespace Core {
+
+static String get_salt()
+{
+    char random_data[12];
+    AK::fill_with_random(random_data, sizeof(random_data));
+
+    StringBuilder builder;
+    builder.append("$5$");
+    builder.append(encode_base64(ReadonlyBytes(random_data, sizeof(random_data))));
+
+    return builder.build();
+}
+
+static Vector<gid_t> get_gids(const StringView& username)
+{
+    Vector<gid_t> extra_gids;
+    for (auto* group = getgrent(); group; group = getgrent()) {
+        for (size_t i = 0; group->gr_mem[i]; ++i) {
+            if (username == group->gr_mem[i]) {
+                extra_gids.append(group->gr_gid);
+                break;
+            }
+        }
+    }
+    endgrent();
+    return extra_gids;
+}
+
+Result<Account, String> Account::from_name(const char* username)
+{
+    struct passwd* pwd = nullptr;
+    errno = 0;
+    pwd = getpwnam(username);
+    if (!pwd) {
+        if (errno == 0)
+            return String("No such user");
+
+        return String(strerror(errno));
+    }
+
+    Account account(pwd, get_gids(pwd->pw_name));
+    endpwent();
+    return account;
+}
+
+Result<Account, String> Account::from_uid(uid_t uid)
+{
+    struct passwd* pwd = nullptr;
+    errno = 0;
+    pwd = getpwuid(uid);
+    if (!pwd) {
+        if (errno == 0)
+            return String("No such user");
+
+        return String(strerror(errno));
+    }
+
+    Account account(pwd, get_gids(pwd->pw_name));
+    endpwent();
+    return account;
+}
+
+bool Account::authenticate(const char* password) const
+{
+    // An empty passwd field indicates that no password is required to log in.
+    if (m_password_hash.is_empty())
+        return true;
+
+    // FIXME: Use crypt_r if it can be built in lagom.
+    char* hash = crypt(password, m_password_hash.characters());
+    return hash != nullptr && strcmp(hash, m_password_hash.characters()) == 0;
+}
+
+bool Account::login() const
+{
+    if (setgroups(m_extra_gids.size(), m_extra_gids.data()) < 0)
+        return false;
+
+    if (setgid(m_gid) < 0)
+        return false;
+
+    if (setuid(m_uid) < 0)
+        return false;
+
+    return true;
+}
+
+void Account::set_password(const char* password)
+{
+    m_password_hash = crypt(password, get_salt().characters());
+}
+
+void Account::set_password_enabled(bool enabled)
+{
+    if (enabled && m_password_hash != "" && m_password_hash[0] == '!') {
+        m_password_hash = m_password_hash.substring(1, m_password_hash.length() - 1);
+    } else if (!enabled && (m_password_hash == "" || m_password_hash[0] != '!')) {
+        StringBuilder builder;
+        builder.append('!');
+        builder.append(m_password_hash);
+        m_password_hash = builder.build();
+    }
+}
+
+void Account::delete_password()
+{
+    m_password_hash = "";
+}
+
+Account::Account(struct passwd* pwd, Vector<gid_t> extra_gids)
+    : m_username(pwd->pw_name)
+    , m_password_hash(pwd->pw_passwd)
+    , m_uid(pwd->pw_uid)
+    , m_gid(pwd->pw_gid)
+    , m_gecos(pwd->pw_gecos)
+    , m_home_directory(pwd->pw_dir)
+    , m_shell(pwd->pw_shell)
+    , m_extra_gids(extra_gids)
+{
+}
+
+bool Account::sync()
+{
+    StringBuilder new_passwd_file;
+
+    setpwent();
+
+    struct passwd* p;
+    errno = 0;
+    while ((p = getpwent())) {
+        if (p->pw_uid == m_uid) {
+            new_passwd_file.appendf("%s:%s:%u:%u:%s:%s:%s\n",
+                m_username.characters(),
+                m_password_hash.characters(),
+                m_uid, m_gid,
+                m_gecos.characters(),
+                m_home_directory.characters(),
+                m_shell.characters());
+
+        } else {
+            new_passwd_file.appendf("%s:%s:%u:%u:%s:%s:%s\n",
+                p->pw_name, p->pw_passwd, p->pw_uid,
+                p->pw_gid, p->pw_gecos, p->pw_dir,
+                p->pw_shell);
+        }
+    }
+    endpwent();
+
+    if (errno)
+        return false;
+
+    String contents = new_passwd_file.build();
+
+    FILE* passwd_file = fopen("/etc/passwd", "w");
+    if (!passwd_file)
+        return false;
+
+    fwrite(contents.characters(), 1, contents.length(), passwd_file);
+    if (ferror(passwd_file)) {
+        int error = ferror(passwd_file);
+        fclose(passwd_file);
+        errno = error;
+        return false;
+    }
+
+    fclose(passwd_file);
+    return true;
+    // FIXME: Sync extra groups.
+}
+}

Libraries/LibCore/Account.h

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2020, Peter Elliott <pelliott@ualberta.ca>
+ * All rights reserved.
+ *
+ * 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, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT HOLDER OR CONTRIBUTORS 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.
+ */
+
+#pragma once
+
+#include <AK/Result.h>
+#include <AK/String.h>
+#include <AK/Types.h>
+#include <AK/Vector.h>
+#include <pwd.h>
+#include <sys/types.h>
+
+namespace Core {
+
+class Account {
+public:
+    static Result<Account, String> from_name(const char* username);
+    static Result<Account, String> from_uid(uid_t uid);
+
+    bool authenticate(const char* password) const;
+    bool login() const;
+
+    String username() const { return m_username; }
+    String password_hash() const { return m_password_hash; }
+
+    // Setters only affect in-memory copy of password.
+    // You must call sync to apply changes.
+    void set_password(const char* password);
+    void set_password_enabled(bool enabled);
+    void delete_password();
+    bool has_password() const { return !m_password_hash.is_empty(); }
+
+    uid_t uid() const { return m_uid; }
+    gid_t gid() const { return m_gid; }
+    const String& gecos() const { return m_gecos; }
+    const String& home_directory() const { return m_home_directory; }
+    const String& shell() const { return m_shell; }
+    const Vector<gid_t>& extra_gids() const { return m_extra_gids; }
+
+    bool sync();
+
+private:
+    Account(struct passwd* pwd, Vector<gid_t> extra_gids);
+
+    String m_username;
+
+    // Contents of passwd field in passwd entry.
+    // Can be empty, "x", or contain a leading '!'
+    String m_password_hash;
+    uid_t m_uid { 0 };
+    gid_t m_gid { 0 };
+    String m_gecos;
+    String m_home_directory;
+    String m_shell;
+    Vector<gid_t> m_extra_gids;
+};
+
+}

Libraries/LibCore/CMakeLists.txt

@@ -1,4 +1,5 @@
 set(SOURCES
+    Account.cpp
     ArgsParser.cpp
     ConfigFile.cpp
     Command.cpp