partial hw1

Author: chengscott

.gitignore

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+source

Makefile

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+CC=gcc
+CFLAGS=-g
+
+source: source.c builtin.c
+	cc ${CFLAGS} source.c builtin.c -o source
+
+.PHONY: clean
+clean:
+	rm -f source

README.md

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+# Secure Interactive Shell
+##### hw1
+
+

builtin.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#define N 1024
+
+int builtin_cat(char *cmd) { return 0; }
+
+int builtin_cd(char *line) {
+  char cmd[N], arg[N], extra[N];
+  if (sscanf(line, "%s %s %s", cmd, arg, extra) != 2) return -1;
+
+  int ret = chdir(arg);
+  // if (ret == -1)
+  return 0;
+}
+
+int builtin_chmod(char *cmd) { return 0; }
+
+int builtin_echo(char *cmd) { return 0; }
+
+int builtin_exit(char *line) {
+  char cmd[N], extra[N];
+  if (sscanf(line, "%s %s", cmd, extra) != 1) return -1;
+
+  return 1;
+}
+
+int builtin_find(char *cmd) { return 0; }
+
+int builtin_help(char *line) {
+  char cmd[N], extra[N];
+  if (sscanf(line, "%s %s", cmd, extra) != 1) return -1;
+
+  const char *help_string[] = {
+      "cat {file}:              Display content of {file}.",
+      "cd {dir}:                Switch current working directory to {dir}.",
+      "chmod {mode} {file/dir}: Change the mode (permission) of a file or "
+      "directory.",
+      "                         {mode} is an octal number.",
+      "                         Please do not follow symbolc links.",
+      "echo {str} [filename]:   Display {str}. If [filename] is given,",
+      "                         open [filename] and append {str} to the file.",
+      "exit:                    Leave the shell.",
+      "find [dir]:              List files/dirs in the current working "
+      "directory",
+      "                         or [dir] if it is given.",
+      "                         Minimum outputs contatin file type, size, and "
+      "name.",
+      "help:                    Display help message.",
+      "id:                      Show current euid and egid.",
+      "mkdir {dir}:             Create a new directory {dir}.",
+      "pwd:                     Print the current working directory.",
+      "rm {file}:               Remove a file.",
+      "rmdir {dir}:             Remove an empty directory.",
+      "stat {file/dir}:         Display detailed information of the given "
+      "file/dir.",
+      "touch {file}:            Create {file} if it does not exist,",
+      "                         or update its access and modification "
+      "timestamp.",
+      "umask {mode}:            Change the umask of the current session."};
+  size_t len = sizeof(help_string) / sizeof(char *);
+  for (size_t i = 0; i < len; ++i) printf("%s\n", help_string[i]);
+  return 0;
+}
+
+int builtin_id(char *line) {
+  char cmd[N], extra[N];
+  if (sscanf(line, "%s %s", cmd, extra) != 1) return -1;
+
+  printf("uid=%d gid=%d\n", geteuid(), getegid());
+  return 0;
+}
+
+int builtin_mkdir(char *line) {
+  char cmd[N], arg[N], extra[N];
+  if (sscanf(line, "%s %s %s", cmd, arg, extra) != 2) return -1;
+
+  int ret = mkdir(arg, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
+  // if (ret == -1)
+  return 0;
+}
+
+int builtin_pwd(char *line) {
+  char cmd[N], extra[N];
+  if (sscanf(line, "%s %s", cmd, extra) != 1) return -1;
+
+  char name[N];
+  getcwd(name, N);
+  // if (name == NULL)
+  printf("%s\n", name);
+  return 0;
+}
+
+int builtin_rm(char *line) {
+  char cmd[N], arg[N], extra[N];
+  if (sscanf(line, "%s %s %s", cmd, arg, extra) != 2) return -1;
+
+  int ret = remove(arg);
+  // if (ret == -1)
+  return 0;
+}
+
+int builtin_rmdir(char *line) {
+  char cmd[N], arg[N], extra[N];
+  if (sscanf(line, "%s %s %s", cmd, arg, extra) != 2) return -1;
+
+  int ret = rmdir(arg);
+  // if (ret == -1)
+  return 0;
+}
+
+int builtin_stat(char *cmd) { return 0; }
+
+int builtin_touch(char *line) {
+  char cmd[N], arg[N], extra[N];
+  if (sscanf(line, "%s %s %s", cmd, arg, extra) != 2) return -1;
+
+  FILE *file;
+  // if (access(arg, F_OK) != -1)
+  file = fopen(arg, "a+");
+  fclose(file);
+  return 0;
+}
+
+int builtin_unmask(char *cmd) { return 0; }

builtin.h

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+int builtin_cat(char *);
+int builtin_cd(char *);
+int builtin_chmod(char *);
+int builtin_echo(char *);
+int builtin_exit(char *);
+int builtin_find(char *);
+int builtin_help(char *);
+int builtin_id(char *);
+int builtin_mkdir(char *);
+int builtin_pwd(char *);
+int builtin_rm(char *);
+int builtin_rmdir(char *);
+int builtin_stat(char *);
+int builtin_touch(char *);
+int builtin_unmask(char *);
+const char *builtin_name[] = {"cat",  "cd",    "chmod", "echo",  "exit",
+                              "find", "help",  "id",    "mkdir", "pwd",
+                              "rm",   "rmdir", "stat",  "touch", "unmask"};
+const int (*builtin_func[])(char *) = {
+    &builtin_cat,   &builtin_cd,    &builtin_chmod, &builtin_echo,
+    &builtin_exit,  &builtin_find,  &builtin_help,  &builtin_id,
+    &builtin_mkdir, &builtin_pwd,   &builtin_rm,    &builtin_rmdir,
+    &builtin_stat,  &builtin_touch, &builtin_unmask};

source.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "builtin.h"
+
+int EUID, EGID;
+int arg_parse(int, char **);
+void shell();
+int shell_exec(char *);
+
+int main(int argc, char **argv) {
+  if (arg_parse(argc, argv) == -1) {
+    return EXIT_FAILURE;
+  }
+
+  shell();
+
+  return EXIT_SUCCESS;
+}
+
+int arg_parse(int argc, char **argv) {
+  if (argc == 3) {
+    // Q: shoud throw parsing error?
+    EUID = atoi(argv[1]);
+    EGID = atoi(argv[2]);
+    return 0;
+  }
+  fprintf(stderr, "Usage: %s {UID} {GID}\n", argv[0]);
+  return -1;
+}
+
+void shell() {
+  char *cmd = NULL;
+  size_t len = 0;
+  int eof = 0;
+  do {
+    printf("~> ");
+    // Q: Can it be killed by C-c?
+    eof = getline(&cmd, &len, stdin);
+    if (eof != -1) eof = shell_exec(cmd);
+    // cleanup
+    free(cmd);
+    cmd = NULL;
+    len = 0;
+  } while (eof != -1);
+}
+
+int shell_exec(char *line) {
+  char cmd[1024], extra[1024];
+  if (sscanf(line, "%s %s", cmd, extra) == -1) return 0;
+  const size_t len = sizeof(builtin_name) / sizeof(char *);
+  for (size_t i = 0; i < len; ++i) {
+    if (strcmp(cmd, builtin_name[i]) == 0) {
+      int ret = (*builtin_func[i])(line);
+      if (ret == 1) return -1;
+      if (ret == -1) fprintf(stderr, "Too many arguments\n");
+      return 0;
+    }
+  }
+  fprintf(stderr, "Unknown command. Type 'help' for help\n");
+  return 0;
+}