Userland: Add userdel program (#1217)

Base/usr/share/man/man8/userdel.md

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+## Name
+
+userdel - delete a user account
+
+## Synopsis
+
+```**sh
+# userdel [-r] <login>
+```
+
+## Description
+
+This program deletes a user account in the system.
+
+This program must be run as root.
+
+## Options
+
+* `-r`, `--remove`: Remove the home directory for this user if the directory exists.
+
+## Exit Values
+
+* 0 - Success
+* 1 - Couldn't update the password file
+* 6 - Specified user doesn't exist
+* 12 - Couldn't remove home directory
+
+## Files
+
+* `/etc/passwd` - user information (such as UID and GID) in this file is deleted.
+* `/home/` - user home directroy is deleted if the `-r` flag is specified.
+
+## Examples
+
+```sh
+# userdel alice
+# userdel -r alice
+# userdel --remove alice
+```
+
+## See Also
+
+* [`useradd`(8)](useradd.md)

Userland/userdel.cpp

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+/*
+ * Copyright (c) 2019-2020, Fei Wu <f.eiwu@yahoo.com>
+ * 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/String.h>
+#include <AK/StringBuilder.h>
+#include <LibCore/ArgsParser.h>
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+int main(int argc, char** argv)
+{
+    const char* username = nullptr;
+    bool remove_home = false;
+
+    Core::ArgsParser args_parser;
+    args_parser.add_option(remove_home, "Remove home directory", "remove", 'r');
+    args_parser.add_positional_argument(username, "Login user identity (username)", "login");
+    args_parser.parse(argc, argv);
+
+    char temp_filename[] = "/etc/passwd.XXXXXX";
+    auto fd = mkstemp(temp_filename);
+    if (fd == -1) {
+        perror("failed to create temporary file");
+        return 1;
+    }
+
+    FILE* temp_file = fdopen(fd, "w");
+    if (!temp_file) {
+        perror("fdopen");
+        if (unlink(temp_filename) < 0) {
+            perror("unlink");
+        }
+
+        return 1;
+    }
+
+    bool user_exists = false;
+    String home_directory;
+
+    int rc = 0;
+    setpwent();
+    for (auto* pw = getpwent(); pw; pw = getpwent()) {
+        if (strcmp(pw->pw_name, username)) {
+            if (putpwent(pw, temp_file) != 0) {
+                perror("failed to put an entry in the temporary passwd file");
+                rc = 1;
+                break;
+            }
+        } else {
+            user_exists = true;
+            if (remove_home)
+                home_directory = pw->pw_dir;
+        }
+    }
+    endpwent();
+
+    if (fclose(temp_file)) {
+        perror("fclose");
+        if (!rc)
+            rc = 1;
+    }
+
+    if (rc == 0 && !user_exists) {
+        fprintf(stderr, "specified user doesn't exist\n");
+        rc = 6;
+    }
+
+    if (rc == 0 && chmod(temp_filename, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)) {
+        perror("chmod");
+        rc = 1;
+    }
+
+    if (rc == 0 && rename(temp_filename, "/etc/passwd") < 0) {
+        perror("failed to rename the temporary passwd file");
+        rc = 1;
+    }
+
+    if (rc) {
+        if (unlink(temp_filename) < 0) {
+            perror("unlink");
+        }
+        return rc;
+    }
+
+    if (remove_home) {
+        if (home_directory == "/") {
+            fprintf(stderr, "home directory is /, not deleted!\n");
+            return 12;
+        }
+
+        if (access(home_directory.characters(), F_OK) != -1) {
+            auto child = fork();
+
+            if (child < 0) {
+                perror("fork");
+                return 12;
+            }
+
+            if (!child) {
+                int rc = execl("/bin/rm", "rm", "-r", home_directory.characters(), nullptr);
+                ASSERT(rc < 0);
+                perror("execl");
+                exit(127);
+            }
+
+            int wstatus;
+            if (waitpid(child, &wstatus, 0) < 0) {
+                perror("waitpid");
+                return 12;
+            }
+            if (WEXITSTATUS(wstatus)) {
+                fprintf(stderr, "failed to remove the home directory\n");
+                return 12;
+            }
+        }
+    }
+
+    return 0;
+}