| 1 | //! On-disk state: the auth token and the explicitly-paired origin list. |
| 2 | //! |
| 3 | //! Both live in a 0700 config dir. The token file is 0600 and we *refuse to use |
| 4 | //! it* if the mode ever loosens — on a multi-user box, 127.0.0.1 is reachable by |
| 5 | //! every local uid, so the file mode is the only thing keeping other users out. |
| 6 | |
| 7 | use std::fs; |
| 8 | use std::io::{self, Write}; |
| 9 | use std::os::unix::fs::{OpenOptionsExt, PermissionsExt}; |
| 10 | use std::path::{Path, PathBuf}; |
| 11 | |
| 12 | pub const TOKEN_BYTES: usize = 32; |
| 13 | |
| 14 | #[derive(Debug)] |
| 15 | pub enum TokenError { |
| 16 | Io(io::Error), |
| 17 | /// The token file is readable by group or other. Refuse rather than |
| 18 | /// silently authenticate against a world-readable secret. |
| 19 | TooPermissive { path: PathBuf, mode: u32 }, |
| 20 | Malformed, |
| 21 | } |
| 22 | |
| 23 | impl std::fmt::Display for TokenError { |
| 24 | fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { |
| 25 | match self { |
| 26 | TokenError::Io(e) => write!(f, "{e}"), |
| 27 | TokenError::TooPermissive { path, mode } => write!( |
| 28 | f, |
| 29 | "token file {} has mode {:04o}; expected 0600. \ |
| 30 | Fix with: chmod 600 {}", |
| 31 | path.display(), |
| 32 | mode, |
| 33 | path.display() |
| 34 | ), |
| 35 | TokenError::Malformed => write!(f, "token file is empty or malformed"), |
| 36 | } |
| 37 | } |
| 38 | } |
| 39 | |
| 40 | impl std::error::Error for TokenError {} |
| 41 | |
| 42 | impl From<io::Error> for TokenError { |
| 43 | fn from(e: io::Error) -> Self { |
| 44 | TokenError::Io(e) |
| 45 | } |
| 46 | } |
| 47 | |
| 48 | pub fn config_dir() -> PathBuf { |
| 49 | if let Some(x) = std::env::var_os("TERMBRIDGE_CONFIG_DIR") { |
| 50 | return PathBuf::from(x); |
| 51 | } |
| 52 | let base = std::env::var_os("XDG_CONFIG_HOME") |
| 53 | .map(PathBuf::from) |
| 54 | .unwrap_or_else(|| { |
| 55 | let home = std::env::var_os("HOME").map(PathBuf::from).unwrap_or_default(); |
| 56 | home.join(".config") |
| 57 | }); |
| 58 | base.join("termbridge") |
| 59 | } |
| 60 | |
| 61 | pub fn token_path() -> PathBuf { |
| 62 | config_dir().join("token") |
| 63 | } |
| 64 | |
| 65 | pub fn paired_origins_path() -> PathBuf { |
| 66 | config_dir().join("paired-origins") |
| 67 | } |
| 68 | |
| 69 | fn ensure_config_dir(dir: &Path) -> io::Result<()> { |
| 70 | fs::create_dir_all(dir)?; |
| 71 | // 0700: the dir itself should not be traversable by other users. |
| 72 | fs::set_permissions(dir, fs::Permissions::from_mode(0o700)) |
| 73 | } |
| 74 | |
| 75 | /// Generate a fresh CSPRNG token and write it 0600, replacing any existing one. |
| 76 | pub fn generate_token(dir: &Path) -> Result<String, TokenError> { |
| 77 | ensure_config_dir(dir)?; |
| 78 | let token = random_hex(TOKEN_BYTES); |
| 79 | let path = dir.join("token"); |
| 80 | |
| 81 | // Create with 0600 *at open time* — never create-then-chmod, which leaves a |
| 82 | // window where the secret is world-readable. |
| 83 | let mut f = fs::OpenOptions::new() |
| 84 | .write(true) |
| 85 | .create(true) |
| 86 | .truncate(true) |
| 87 | .mode(0o600) |
| 88 | .open(&path)?; |
| 89 | f.write_all(token.as_bytes())?; |
| 90 | f.write_all(b"\n")?; |
| 91 | f.sync_all()?; |
| 92 | |
| 93 | // An existing file keeps its old mode through O_CREAT, so enforce it too. |
| 94 | fs::set_permissions(&path, fs::Permissions::from_mode(0o600))?; |
| 95 | Ok(token) |
| 96 | } |
| 97 | |
| 98 | /// Load the token, refusing if the file is group/other accessible. |
| 99 | pub fn load_token(dir: &Path) -> Result<String, TokenError> { |
| 100 | let path = dir.join("token"); |
| 101 | let meta = fs::metadata(&path)?; |
| 102 | let mode = meta.permissions().mode() & 0o777; |
| 103 | if mode & 0o077 != 0 { |
| 104 | return Err(TokenError::TooPermissive { path, mode }); |
| 105 | } |
| 106 | let token = fs::read_to_string(&path)?.trim().to_string(); |
| 107 | if token.is_empty() { |
| 108 | return Err(TokenError::Malformed); |
| 109 | } |
| 110 | Ok(token) |
| 111 | } |
| 112 | |
| 113 | pub fn load_or_create_token(dir: &Path) -> Result<String, TokenError> { |
| 114 | match load_token(dir) { |
| 115 | Ok(t) => Ok(t), |
| 116 | Err(TokenError::Io(e)) if e.kind() == io::ErrorKind::NotFound => generate_token(dir), |
| 117 | Err(e) => Err(e), |
| 118 | } |
| 119 | } |
| 120 | |
| 121 | /// Origins the user has *explicitly* approved. Absence of this file means no |
| 122 | /// client can connect — pairing is never implicit. |
| 123 | pub fn load_paired_origins(dir: &Path) -> Vec<String> { |
| 124 | let path = dir.join("paired-origins"); |
| 125 | let Ok(contents) = fs::read_to_string(path) else { |
| 126 | return Vec::new(); |
| 127 | }; |
| 128 | contents |
| 129 | .lines() |
| 130 | .map(str::trim) |
| 131 | .filter(|l| !l.is_empty() && !l.starts_with('#')) |
| 132 | .map(|l| l.to_ascii_lowercase()) |
| 133 | .collect() |
| 134 | } |
| 135 | |
| 136 | pub fn pair_origin(dir: &Path, origin: &str) -> io::Result<bool> { |
| 137 | ensure_config_dir(dir)?; |
| 138 | let origin = origin.trim().to_ascii_lowercase(); |
| 139 | let mut existing = load_paired_origins(dir); |
| 140 | if existing.iter().any(|o| o == &origin) { |
| 141 | return Ok(false); |
| 142 | } |
| 143 | existing.push(origin); |
| 144 | let path = dir.join("paired-origins"); |
| 145 | let mut f = fs::OpenOptions::new() |
| 146 | .write(true) |
| 147 | .create(true) |
| 148 | .truncate(true) |
| 149 | .mode(0o600) |
| 150 | .open(&path)?; |
| 151 | writeln!(f, "# Origins approved to connect to termbridge. One per line.")?; |
| 152 | for o in &existing { |
| 153 | writeln!(f, "{o}")?; |
| 154 | } |
| 155 | Ok(true) |
| 156 | } |
| 157 | |
| 158 | pub fn unpair_origin(dir: &Path, origin: &str) -> io::Result<bool> { |
| 159 | let origin = origin.trim().to_ascii_lowercase(); |
| 160 | let existing = load_paired_origins(dir); |
| 161 | if !existing.iter().any(|o| o == &origin) { |
| 162 | return Ok(false); |
| 163 | } |
| 164 | let path = dir.join("paired-origins"); |
| 165 | let mut f = fs::OpenOptions::new() |
| 166 | .write(true) |
| 167 | .create(true) |
| 168 | .truncate(true) |
| 169 | .mode(0o600) |
| 170 | .open(&path)?; |
| 171 | writeln!(f, "# Origins approved to connect to termbridge. One per line.")?; |
| 172 | for o in existing.iter().filter(|o| *o != &origin) { |
| 173 | writeln!(f, "{o}")?; |
| 174 | } |
| 175 | Ok(true) |
| 176 | } |
| 177 | |
| 178 | fn random_hex(n: usize) -> String { |
| 179 | let mut buf = vec![0u8; n]; |
| 180 | // Straight from the OS CSPRNG. Deliberately not a userspace PRNG — this is |
| 181 | // the only thing standing between another local uid and a shell. |
| 182 | getrandom::fill(&mut buf).expect("OS CSPRNG unavailable"); |
| 183 | let mut s = String::with_capacity(n * 2); |
| 184 | for b in buf { |
| 185 | use std::fmt::Write as _; |
| 186 | let _ = write!(s, "{b:02x}"); |
| 187 | } |
| 188 | s |
| 189 | } |