1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374
// Copyright 2015-2016 Brian Smith.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
//! untrusted.rs: Safe, fast, zero-panic, zero-crashing, zero-allocation
//! parsing of untrusted inputs in Rust.
//!
//! <code>git clone https://github.com/briansmith/untrusted</code>
//!
//! untrusted.rs goes beyond Rust's normal safety guarantees by also
//! guaranteeing that parsing will be panic-free, as long as
//! `untrusted::Input::as_slice_less_safe()` is not used. It avoids copying
//! data and heap allocation and strives to prevent common pitfalls such as
//! accidentally parsing input bytes multiple times. In order to meet these
//! goals, untrusted.rs is limited in functionality such that it works best for
//! input languages with a small fixed amount of lookahead such as ASN.1, TLS,
//! TCP/IP, and many other networking, IPC, and related protocols. Languages
//! that require more lookahead and/or backtracking require some significant
//! contortions to parse using this framework. It would not be realistic to use
//! it for parsing programming language code, for example.
//!
//! The overall pattern for using untrusted.rs is:
//!
//! 1. Write a recursive-descent-style parser for the input language, where the
//! input data is given as a `&mut untrusted::Reader` parameter to each
//! function. Each function should have a return type of `Result<V, E>` for
//! some value type `V` and some error type `E`, either or both of which may
//! be `()`. Functions for parsing the lowest-level language constructs
//! should be defined. Those lowest-level functions will parse their inputs
//! using `::read_byte()`, `Reader::peek()`, and similar functions.
//! Higher-level language constructs are then parsed by calling the
//! lower-level functions in sequence.
//!
//! 2. Wrap the top-most functions of your recursive-descent parser in
//! functions that take their input data as an `untrusted::Input`. The
//! wrapper functions should call the `Input`'s `read_all` (or a variant
//! thereof) method. The wrapper functions are the only ones that should be
//! exposed outside the parser's module.
//!
//! 3. After receiving the input data to parse, wrap it in an `untrusted::Input`
//! using `untrusted::Input::from()` as early as possible. Pass the
//! `untrusted::Input` to the wrapper functions when they need to be parsed.
//!
//! In general parsers built using `untrusted::Reader` do not need to explicitly
//! check for end-of-input unless they are parsing optional constructs, because
//! `Reader::read_byte()` will return `Err(EndOfInput)` on end-of-input.
//! Similarly, parsers using `untrusted::Reader` generally don't need to check
//! for extra junk at the end of the input as long as the parser's API uses the
//! pattern described above, as `read_all` and its variants automatically check
//! for trailing junk. `Reader::skip_to_end()` must be used when any remaining
//! unread input should be ignored without triggering an error.
//!
//! untrusted.rs works best when all processing of the input data is done
//! through the `untrusted::Input` and `untrusted::Reader` types. In
//! particular, avoid trying to parse input data using functions that take
//! byte slices. However, when you need to access a part of the input data as
//! a slice to use a function that isn't written using untrusted.rs,
//! `Input::as_slice_less_safe()` can be used.
//!
//! It is recommend to use `use untrusted;` and then `untrusted::Input`,
//! `untrusted::Reader`, etc., instead of using `use untrusted::*`. Qualifying
//! the names with `untrusted` helps remind the reader of the code that it is
//! dealing with *untrusted* input.
//!
//! # Examples
//!
//! [*ring*](https://github.com/briansmith/ring)'s parser for the subset of
//! ASN.1 DER it needs to understand,
//! [`ring::der`](https://github.com/briansmith/ring/blob/master/src/der.rs),
//! is built on top of untrusted.rs. *ring* also uses untrusted.rs to parse ECC
//! public keys, RSA PKCS#1 1.5 padding, and for all other parsing it does.
//!
//! All of [webpki](https://github.com/briansmith/webpki)'s parsing of X.509
//! certificates (also ASN.1 DER) is done using untrusted.rs.
#![doc(html_root_url = "https://briansmith.org/rustdoc/")]
// `#[derive(...)]` uses `#[allow(unused_qualifications)]` internally.
#![deny(unused_qualifications)]
#![forbid(
anonymous_parameters,
box_pointers,
missing_docs,
trivial_casts,
trivial_numeric_casts,
unsafe_code,
unstable_features,
unused_extern_crates,
unused_import_braces,
unused_results,
variant_size_differences,
warnings
)]
#![no_std]
/// A wrapper around `&'a [u8]` that helps in writing panic-free code.
///
/// No methods of `Input` will ever panic.
#[derive(Clone, Copy, Debug, Eq)]
pub struct Input<'a> {
value: no_panic::Slice<'a>,
}
impl<'a> Input<'a> {
/// Construct a new `Input` for the given input `bytes`.
pub const fn from(bytes: &'a [u8]) -> Self {
// This limit is important for avoiding integer overflow. In particular,
// `Reader` assumes that an `i + 1 > i` if `input.value.get(i)` does
// not return `None`. According to the Rust language reference, the
// maximum object size is `core::isize::MAX`, and in practice it is
// impossible to create an object of size `core::usize::MAX` or larger.
Self {
value: no_panic::Slice::new(bytes),
}
}
/// Returns `true` if the input is empty and false otherwise.
#[inline]
pub fn is_empty(&self) -> bool { self.value.is_empty() }
/// Returns the length of the `Input`.
#[inline]
pub fn len(&self) -> usize { self.value.len() }
/// Calls `read` with the given input as a `Reader`, ensuring that `read`
/// consumed the entire input. If `read` does not consume the entire input,
/// `incomplete_read` is returned.
pub fn read_all<F, R, E>(&self, incomplete_read: E, read: F) -> Result<R, E>
where
F: FnOnce(&mut Reader<'a>) -> Result<R, E>,
{
let mut input = Reader::new(*self);
let result = read(&mut input)?;
if input.at_end() {
Ok(result)
} else {
Err(incomplete_read)
}
}
/// Access the input as a slice so it can be processed by functions that
/// are not written using the Input/Reader framework.
#[inline]
pub fn as_slice_less_safe(&self) -> &'a [u8] { self.value.as_slice_less_safe() }
}
impl<'a> From<&'a [u8]> for Input<'a> {
#[inline]
fn from(value: &'a [u8]) -> Self { Self { value: no_panic::Slice::new(value)} }
}
// #[derive(PartialEq)] would result in lifetime bounds that are
// unnecessarily restrictive; see
// https://github.com/rust-lang/rust/issues/26925.
impl PartialEq<Input<'_>> for Input<'_> {
#[inline]
fn eq(&self, other: &Input) -> bool {
self.as_slice_less_safe() == other.as_slice_less_safe()
}
}
impl PartialEq<[u8]> for Input<'_> {
#[inline]
fn eq(&self, other: &[u8]) -> bool { self.as_slice_less_safe() == other }
}
impl PartialEq<Input<'_>> for [u8] {
#[inline]
fn eq(&self, other: &Input) -> bool { other.as_slice_less_safe() == self }
}
/// Calls `read` with the given input as a `Reader`, ensuring that `read`
/// consumed the entire input. When `input` is `None`, `read` will be
/// called with `None`.
pub fn read_all_optional<'a, F, R, E>(
input: Option<Input<'a>>, incomplete_read: E, read: F,
) -> Result<R, E>
where
F: FnOnce(Option<&mut Reader<'a>>) -> Result<R, E>,
{
match input {
Some(input) => {
let mut input = Reader::new(input);
let result = read(Some(&mut input))?;
if input.at_end() {
Ok(result)
} else {
Err(incomplete_read)
}
},
None => read(None),
}
}
/// A read-only, forward-only* cursor into the data in an `Input`.
///
/// Using `Reader` to parse input helps to ensure that no byte of the input
/// will be accidentally processed more than once. Using `Reader` in
/// conjunction with `read_all` and `read_all_optional` helps ensure that no
/// byte of the input is accidentally left unprocessed. The methods of `Reader`
/// never panic, so `Reader` also assists the writing of panic-free code.
///
/// \* `Reader` is not strictly forward-only because of the method
/// `get_input_between_marks`, which is provided mainly to support calculating
/// digests over parsed data.
#[derive(Debug)]
pub struct Reader<'a> {
input: no_panic::Slice<'a>,
i: usize,
}
/// An index into the already-parsed input of a `Reader`.
pub struct Mark {
i: usize,
}
impl<'a> Reader<'a> {
/// Construct a new Reader for the given input. Use `read_all` or
/// `read_all_optional` instead of `Reader::new` whenever possible.
#[inline]
pub fn new(input: Input<'a>) -> Self {
Self {
input: input.value,
i: 0,
}
}
/// Returns `true` if the reader is at the end of the input, and `false`
/// otherwise.
#[inline]
pub fn at_end(&self) -> bool { self.i == self.input.len() }
/// Returns an `Input` for already-parsed input that has had its boundaries
/// marked using `mark`.
#[inline]
pub fn get_input_between_marks(
&self, mark1: Mark, mark2: Mark,
) -> Result<Input<'a>, EndOfInput> {
self.input
.subslice(mark1.i..mark2.i)
.map(|subslice| Input { value: subslice })
.ok_or(EndOfInput)
}
/// Return the current position of the `Reader` for future use in a call
/// to `get_input_between_marks`.
#[inline]
pub fn mark(&self) -> Mark { Mark { i: self.i } }
/// Returns `true` if there is at least one more byte in the input and that
/// byte is equal to `b`, and false otherwise.
#[inline]
pub fn peek(&self, b: u8) -> bool {
match self.input.get(self.i) {
Some(actual_b) => b == *actual_b,
None => false,
}
}
/// Reads the next input byte.
///
/// Returns `Ok(b)` where `b` is the next input byte, or `Err(EndOfInput)`
/// if the `Reader` is at the end of the input.
#[inline]
pub fn read_byte(&mut self) -> Result<u8, EndOfInput> {
match self.input.get(self.i) {
Some(b) => {
self.i += 1; // safe from overflow; see Input::from().
Ok(*b)
},
None => Err(EndOfInput),
}
}
/// Skips `num_bytes` of the input, returning the skipped input as an
/// `Input`.
///
/// Returns `Ok(i)` if there are at least `num_bytes` of input remaining,
/// and `Err(EndOfInput)` otherwise.
#[inline]
pub fn read_bytes(&mut self, num_bytes: usize) -> Result<Input<'a>, EndOfInput> {
let new_i = self.i.checked_add(num_bytes).ok_or(EndOfInput)?;
let ret = self
.input
.subslice(self.i..new_i)
.map(|subslice| Input { value: subslice })
.ok_or(EndOfInput)?;
self.i = new_i;
Ok(ret)
}
/// Skips the reader to the end of the input, returning the skipped input
/// as an `Input`.
#[inline]
pub fn read_bytes_to_end(&mut self) -> Input<'a> {
let to_skip = self.input.len() - self.i;
self.read_bytes(to_skip).unwrap()
}
/// Calls `read()` with the given input as a `Reader`. On success, returns a
/// pair `(bytes_read, r)` where `bytes_read` is what `read()` consumed and
/// `r` is `read()`'s return value.
pub fn read_partial<F, R, E>(&mut self, read: F) -> Result<(Input<'a>, R), E>
where
F: FnOnce(&mut Reader<'a>) -> Result<R, E>,
{
let start = self.i;
let r = read(self)?;
let bytes_read = Input {
value: self.input.subslice(start..self.i).unwrap()
};
Ok((bytes_read, r))
}
/// Skips `num_bytes` of the input.
///
/// Returns `Ok(i)` if there are at least `num_bytes` of input remaining,
/// and `Err(EndOfInput)` otherwise.
#[inline]
pub fn skip(&mut self, num_bytes: usize) -> Result<(), EndOfInput> {
self.read_bytes(num_bytes).map(|_| ())
}
/// Skips the reader to the end of the input.
#[inline]
pub fn skip_to_end(&mut self) -> () { let _ = self.read_bytes_to_end(); }
}
/// The error type used to indicate the end of the input was reached before the
/// operation could be completed.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct EndOfInput;
mod no_panic {
use core;
/// A wrapper around a slice that exposes no functions that can panic.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Slice<'a> {
bytes: &'a [u8],
}
impl<'a> Slice<'a> {
#[inline]
pub const fn new(bytes: &'a [u8]) -> Self { Self { bytes } }
#[inline]
pub fn get(&self, i: usize) -> Option<&u8> { self.bytes.get(i) }
#[inline]
pub fn subslice(&self, r: core::ops::Range<usize>) -> Option<Self> {
self.bytes.get(r).map(|bytes| Self { bytes })
}
#[inline]
pub fn is_empty(&self) -> bool { self.bytes.is_empty() }
#[inline]
pub fn len(&self) -> usize { self.bytes.len() }
#[inline]
pub fn as_slice_less_safe(&self) -> &'a [u8] { self.bytes }
}
} // mod no_panic