170 lines
2.8 KiB
C++
170 lines
2.8 KiB
C++
#include <BAN/String.h>
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#include <BAN/Optional.h>
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#include <BAN/Vector.h>
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#include <ctype.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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struct User
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{
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BAN::String name;
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uid_t uid;
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gid_t gid;
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BAN::String home;
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BAN::String shell;
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};
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BAN::Optional<id_t> parse_id(BAN::StringView value)
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{
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// NOTE: we only allow 10^9 uids
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if (value.size() < 1 || value.size() > 9)
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return {};
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id_t id { 0 };
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for (char c : value)
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{
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if (!isdigit(c))
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return {};
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id = (id * 10) + (c - '0');
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}
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return id;
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}
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BAN::Optional<User> parse_user(BAN::StringView line)
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{
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auto parts = MUST(line.split(':', true));
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if (parts.size() != 7)
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return {};
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User user;
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user.name = parts[0];
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user.uid = ({ auto id = parse_id(parts[2]); if (!id.has_value()) return {}; id.value(); });
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user.gid = ({ auto id = parse_id(parts[3]); if (!id.has_value()) return {}; id.value(); });
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user.home = parts[5];
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user.shell = parts[6];
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return user;
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}
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BAN::Vector<User> parse_users()
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{
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FILE* fp = fopen("/etc/passwd", "r");
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if (fp == nullptr)
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{
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fprintf(stderr, "could not open /etc/passwd\n");
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perror("fopen");
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}
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BAN::Vector<User> users;
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char buffer[1024];
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while (fgets(buffer, sizeof(buffer), fp))
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{
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*strchrnul(buffer, '\n') = '\0';
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auto user = parse_user(buffer);
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if (user.has_value())
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MUST(users.push_back(user.release_value()));
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}
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if (ferror(fp))
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{
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perror("fread");
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fclose(fp);
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return {};
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}
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fclose(fp);
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return users;
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}
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void initialize_stdio()
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{
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char tty[L_ctermid];
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ctermid(tty);
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if (open(tty, O_RDONLY) != 0) _exit(1);
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if (open(tty, O_WRONLY) != 1) _exit(1);
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if (open(tty, O_WRONLY) != 2) _exit(1);
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}
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int main()
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{
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initialize_stdio();
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bool first = true;
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while (true)
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{
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auto users = parse_users();
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char name_buffer[128];
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BAN::StringView name;
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if (first)
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{
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name = "user"sv;
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first = false;
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}
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while (name.empty())
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{
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printf("username: ");
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fflush(stdout);
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size_t nread = fread(name_buffer, 1, sizeof(name_buffer) - 1, stdin);
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if (nread == 0)
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{
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if (ferror(stdin))
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{
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fprintf(stderr, "Could not read from stdin\n");
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return 1;
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}
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continue;
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}
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if (nread == 1)
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continue;
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name = BAN::StringView(name_buffer, nread - 1);
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break;
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}
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for (const User& user : users)
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{
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if (user.name == name)
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{
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pid_t pid = fork();
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if (pid == 0)
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{
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printf("Welcome back %s!\n", user.name.data());
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if (setgid(user.gid) == -1)
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perror("setgid");
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if (setuid(user.uid) == -1)
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perror("setuid");
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setenv("HOME", user.home.data(), 1);
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chdir(user.home.data());
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execl(user.shell.data(), user.shell.data(), nullptr);
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perror("execl");
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exit(1);
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}
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if (pid == -1)
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{
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perror("fork");
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break;
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}
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int status;
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waitpid(pid, &status, 0);
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}
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}
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}
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}
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