banan-os/userspace/init/main.cpp

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