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fix(nix-compat/bytes): make BytesReader less hazardous

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We now *never* return the final bytes until we've read the padding
in full, so read_exact is safe to use.

This is implemented by TrailerReader, which splits the phases of
reading (and validating) the final 8-byte block, and providing
the contained payload bytes to the caller.

Change-Id: I0d05946a8af9c260a18d71d2b763ba7a68b3c27f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11518
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
This commit is contained in:
edef 2024-04-25 23:27:58 +00:00
parent 70c679eac4
commit ba46b1818a
2 changed files with 321 additions and 182 deletions
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471
tvix/nix-compat/src/wire/bytes/reader/mod.rs Normal file
View file

@ -0,0 +1,471 @@
use std::{
io,
ops::{Bound, RangeBounds},
pin::Pin,
task::{self, ready, Poll},
};
use tokio::io::{AsyncRead, ReadBuf};
use trailer::TrailerReader;
mod trailer;
/// Reads a "bytes wire packet" from the underlying reader.
/// The format is the same as in [crate::wire::bytes::read_bytes],
/// however this structure provides a [AsyncRead] interface,
/// allowing to not having to pass around the entire payload in memory.
///
/// After being constructed with the underlying reader and an allowed size,
/// subsequent requests to poll_read will return payload data until the end
/// of the packet is reached.
///
/// Internally, it will first read over the size packet, filling payload_size,
/// ensuring it fits allowed_size, then return payload data.
///
/// It will not return the final bytes before all padding has been successfully
/// consumed as well, but the full length of the reader must be consumed.
///
/// In case of an error due to size constraints, or in case of not reading
/// all the way to the end (and getting a EOF), the underlying reader is no
/// longer usable and might return garbage.
pub struct BytesReader<R> {
state: State<R>,
}
#[derive(Debug)]
enum State<R> {
Size {
reader: Option<R>,
/// Minimum length (inclusive)
user_len_min: u64,
/// Maximum length (inclusive)
user_len_max: u64,
filled: u8,
buf: [u8; 8],
},
Body {
reader: Option<R>,
consumed: u64,
user_len: u64,
},
Trailer(TrailerReader<R>),
}
impl<R> BytesReader<R>
where
R: AsyncRead + Unpin,
{
/// Constructs a new BytesReader, using the underlying passed reader.
pub fn new<S: RangeBounds<u64>>(reader: R, allowed_size: S) -> Self {
let user_len_min = match allowed_size.start_bound() {
Bound::Included(&n) => n,
Bound::Excluded(&n) => n.saturating_add(1),
Bound::Unbounded => 0,
};
let user_len_max = match allowed_size.end_bound() {
Bound::Included(&n) => n,
Bound::Excluded(&n) => n.checked_sub(1).unwrap(),
Bound::Unbounded => u64::MAX,
};
Self {
state: State::Size {
reader: Some(reader),
user_len_min,
user_len_max,
filled: 0,
buf: [0; 8],
},
}
}
/// Construct a new BytesReader with a known, and already-read size.
pub fn with_size(reader: R, size: u64) -> Self {
Self {
state: State::Body {
reader: Some(reader),
consumed: 0,
user_len: size,
},
}
}
}
impl<R: AsyncRead + Unpin> AsyncRead for BytesReader<R> {
fn poll_read(
self: Pin<&mut Self>,
cx: &mut task::Context,
buf: &mut ReadBuf,
) -> Poll<io::Result<()>> {
let this = &mut self.get_mut().state;
loop {
match this {
State::Size {
reader,
user_len_min,
user_len_max,
filled: 8,
buf,
} => {
let reader = reader.take().unwrap();
let data_len = u64::from_le_bytes(*buf);
if data_len < *user_len_min || data_len > *user_len_max {
return Err(io::Error::new(io::ErrorKind::InvalidData, "invalid size"))
.into();
}
*this = State::Body {
reader: Some(reader),
consumed: 0,
user_len: data_len,
};
}
State::Size {
reader,
filled,
buf,
..
} => {
let reader = reader.as_mut().unwrap();
let mut read_buf = ReadBuf::new(&mut buf[..]);
read_buf.advance(*filled as usize);
ready!(Pin::new(reader).poll_read(cx, &mut read_buf))?;
let new_filled = read_buf.filled().len() as u8;
if *filled == new_filled {
return Err(io::ErrorKind::UnexpectedEof.into()).into();
}
*filled = new_filled;
}
State::Body {
reader,
consumed,
user_len,
} => {
let body_len = *user_len & !7;
let remaining = body_len - *consumed;
let reader = if remaining == 0 {
let reader = reader.take().unwrap();
let user_len = (*user_len & 7) as u8;
*this = State::Trailer(TrailerReader::new(reader, user_len));
continue;
} else {
reader.as_mut().unwrap()
};
let mut bytes_read = 0;
ready!(with_limited(buf, remaining, |buf| {
let ret = Pin::new(reader).poll_read(cx, buf);
bytes_read = buf.initialized().len();
ret
}))?;
*consumed += bytes_read as u64;
return if bytes_read != 0 {
Ok(())
} else {
Err(io::ErrorKind::UnexpectedEof.into())
}
.into();
}
State::Trailer(reader) => {
return Pin::new(reader).poll_read(cx, buf);
}
}
}
}
}
/// Make a limited version of `buf`, consisting only of up to `n` bytes of the unfilled section, and call `f` with it.
/// After `f` returns, we propagate the filled cursor advancement back to `buf`.
fn with_limited<R>(buf: &mut ReadBuf, n: u64, f: impl FnOnce(&mut ReadBuf) -> R) -> R {
let mut nbuf = buf.take(n.try_into().unwrap_or(usize::MAX));
let ptr = nbuf.initialized().as_ptr();
let ret = f(&mut nbuf);
// SAFETY: `ReadBuf::take` only returns the *unfilled* section of `buf`,
// so anything filled is new, initialized data.
//
// We verify that `nbuf` still points to the same buffer,
// so we're sure it hasn't been swapped out.
unsafe {
// ensure our buffer hasn't been swapped out
assert_eq!(nbuf.initialized().as_ptr(), ptr);
let n = nbuf.filled().len();
buf.assume_init(n);
buf.advance(n);
}
ret
}
#[cfg(test)]
mod tests {
use std::time::Duration;
use crate::wire::bytes::{padding_len, write_bytes};
use hex_literal::hex;
use lazy_static::lazy_static;
use rstest::rstest;
use tokio::io::AsyncReadExt;
use tokio_test::{assert_err, io::Builder};
use super::*;
/// The maximum length of bytes packets we're willing to accept in the test
/// cases.
const MAX_LEN: u64 = 1024;
lazy_static! {
pub static ref LARGE_PAYLOAD: Vec<u8> = (0..255).collect::<Vec<u8>>().repeat(4 * 1024);
}
/// Helper function, calling the (simpler) write_bytes with the payload.
/// We use this to create data we want to read from the wire.
async fn produce_packet_bytes(payload: &[u8]) -> Vec<u8> {
let mut exp = vec![];
write_bytes(&mut exp, payload).await.unwrap();
exp
}
/// Read bytes packets of various length, and ensure read_to_end returns the
/// expected payload.
#[rstest]
#[case::empty(&[])] // empty bytes packet
#[case::size_1b(&[0xff])] // 1 bytes payload
#[case::size_8b(&hex!("0001020304050607"))] // 8 bytes payload (no padding)
#[case::size_9b( &hex!("000102030405060708"))] // 9 bytes payload (7 bytes padding)
#[case::size_1m(LARGE_PAYLOAD.as_slice())] // larger bytes packet
#[tokio::test]
async fn read_payload_correct(#[case] payload: &[u8]) {
let mut mock = Builder::new()
.read(&produce_packet_bytes(payload).await)
.build();
let mut r = BytesReader::new(&mut mock, ..=LARGE_PAYLOAD.len() as u64);
let mut buf = Vec::new();
r.read_to_end(&mut buf).await.expect("must succeed");
assert_eq!(payload, &buf[..]);
}
/// Read bytes packets of various length, and ensure read_to_end returns the
/// expected payload.
#[rstest]
#[case::empty(&[])] // empty bytes packet
#[case::size_1b(&[0xff])] // 1 bytes payload
#[case::size_8b(&hex!("0001020304050607"))] // 8 bytes payload (no padding)
#[case::size_9b( &hex!("000102030405060708"))] // 9 bytes payload (7 bytes padding)
#[case::size_1m(LARGE_PAYLOAD.as_slice())] // larger bytes packet
#[tokio::test]
async fn read_payload_correct_known(#[case] payload: &[u8]) {
let packet = produce_packet_bytes(payload).await;
let size = u64::from_le_bytes({
let mut buf = [0; 8];
buf.copy_from_slice(&packet[..8]);
buf
});
let mut mock = Builder::new().read(&packet[8..]).build();
let mut r = BytesReader::with_size(&mut mock, size);
let mut buf = Vec::new();
r.read_to_end(&mut buf).await.expect("must succeed");
assert_eq!(payload, &buf[..]);
}
/// Fail if the bytes packet is larger than allowed
#[tokio::test]
async fn read_bigger_than_allowed_fail() {
let payload = LARGE_PAYLOAD.as_slice();
let mut mock = Builder::new()
.read(&produce_packet_bytes(payload).await[0..8]) // We stop reading after the size packet
.build();
let mut r = BytesReader::new(&mut mock, ..2048);
let mut buf = Vec::new();
assert_err!(r.read_to_end(&mut buf).await);
}
/// Fail if the bytes packet is smaller than allowed
#[tokio::test]
async fn read_smaller_than_allowed_fail() {
let payload = &[0x00, 0x01, 0x02];
let mut mock = Builder::new()
.read(&produce_packet_bytes(payload).await[0..8]) // We stop reading after the size packet
.build();
let mut r = BytesReader::new(&mut mock, 1024..2048);
let mut buf = Vec::new();
assert_err!(r.read_to_end(&mut buf).await);
}
/// Fail if the padding is not all zeroes
#[tokio::test]
async fn read_fail_if_nonzero_padding() {
let payload = &[0x00, 0x01, 0x02];
let mut packet_bytes = produce_packet_bytes(payload).await;
// Flip some bits in the padding
packet_bytes[12] = 0xff;
let mut mock = Builder::new().read(&packet_bytes).build(); // We stop reading after the faulty bit
let mut r = BytesReader::new(&mut mock, ..MAX_LEN);
let mut buf = Vec::new();
r.read_to_end(&mut buf).await.expect_err("must fail");
}
/// Start a 9 bytes payload packet, but have the underlying reader return
/// EOF in the middle of the size packet (after 4 bytes).
/// We should get an unexpected EOF error, already when trying to read the
/// first byte (of payload)
#[tokio::test]
async fn read_9b_eof_during_size() {
let payload = &hex!("FF0102030405060708");
let mut mock = Builder::new()
.read(&produce_packet_bytes(payload).await[..4])
.build();
let mut r = BytesReader::new(&mut mock, ..MAX_LEN);
let mut buf = [0u8; 1];
assert_eq!(
r.read_exact(&mut buf).await.expect_err("must fail").kind(),
std::io::ErrorKind::UnexpectedEof
);
assert_eq!(&[0], &buf, "buffer should stay empty");
}
/// Start a 9 bytes payload packet, but have the underlying reader return
/// EOF in the middle of the payload (4 bytes into the payload).
/// We should get an unexpected EOF error, after reading the first 4 bytes
/// (successfully).
#[tokio::test]
async fn read_9b_eof_during_payload() {
let payload = &hex!("FF0102030405060708");
let mut mock = Builder::new()
.read(&produce_packet_bytes(payload).await[..8 + 4])
.build();
let mut r = BytesReader::new(&mut mock, ..MAX_LEN);
let mut buf = [0; 9];
r.read_exact(&mut buf[..4]).await.expect("must succeed");
assert_eq!(
r.read_exact(&mut buf[4..=4])
.await
.expect_err("must fail")
.kind(),
std::io::ErrorKind::UnexpectedEof
);
}
/// Start a 9 bytes payload packet, but don't supply the necessary padding.
/// This is expected to always fail before returning the final data.
#[rstest]
#[case::before_padding(8 + 9)]
#[case::during_padding(8 + 9 + 2)]
#[case::after_padding(8 + 9 + padding_len(9) as usize - 1)]
#[tokio::test]
async fn read_9b_eof_after_payload(#[case] offset: usize) {
let payload = &hex!("FF0102030405060708");
let mut mock = Builder::new()
.read(&produce_packet_bytes(payload).await[..offset])
.build();
let mut r = BytesReader::new(&mut mock, ..MAX_LEN);
// read_exact of the payload *body* will succeed, but a subsequent read will
// return UnexpectedEof error.
assert_eq!(r.read_exact(&mut [0; 8]).await.unwrap(), 8);
assert_eq!(
r.read_exact(&mut [0]).await.unwrap_err().kind(),
std::io::ErrorKind::UnexpectedEof
);
}
/// Start a 9 bytes payload packet, but return an error after a certain position.
/// Ensure that error is propagated.
#[rstest]
#[case::during_size(4)]
#[case::before_payload(8)]
#[case::during_payload(8 + 4)]
#[case::before_padding(8 + 4)]
#[case::during_padding(8 + 9 + 2)]
#[tokio::test]
async fn propagate_error_from_reader(#[case] offset: usize) {
let payload = &hex!("FF0102030405060708");
let mut mock = Builder::new()
.read(&produce_packet_bytes(payload).await[..offset])
.read_error(std::io::Error::new(std::io::ErrorKind::Other, "foo"))
.build();
let mut r = BytesReader::new(&mut mock, ..MAX_LEN);
let mut buf = Vec::new();
let err = r.read_to_end(&mut buf).await.expect_err("must fail");
assert_eq!(
err.kind(),
std::io::ErrorKind::Other,
"error kind must match"
);
assert_eq!(
err.into_inner().unwrap().to_string(),
"foo",
"error payload must contain foo"
);
}
/// If there's an error right after the padding, we don't propagate it, as
/// we're done reading. We just return EOF.
#[tokio::test]
async fn no_error_after_eof() {
let payload = &hex!("FF0102030405060708");
let mut mock = Builder::new()
.read(&produce_packet_bytes(payload).await)
.read_error(std::io::Error::new(std::io::ErrorKind::Other, "foo"))
.build();
let mut r = BytesReader::new(&mut mock, ..MAX_LEN);
let mut buf = Vec::new();
r.read_to_end(&mut buf).await.expect("must succeed");
assert_eq!(buf.as_slice(), payload);
}
/// Introduce various stalls in various places of the packet, to ensure we
/// handle these cases properly, too.
#[rstest]
#[case::beginning(0)]
#[case::before_payload(8)]
#[case::during_payload(8 + 4)]
#[case::before_padding(8 + 4)]
#[case::during_padding(8 + 9 + 2)]
#[tokio::test]
async fn read_payload_correct_pending(#[case] offset: usize) {
let payload = &hex!("FF0102030405060708");
let mut mock = Builder::new()
.read(&produce_packet_bytes(payload).await[..offset])
.wait(Duration::from_nanos(0))
.read(&produce_packet_bytes(payload).await[offset..])
.build();
let mut r = BytesReader::new(&mut mock, ..=LARGE_PAYLOAD.len() as u64);
let mut buf = Vec::new();
r.read_to_end(&mut buf).await.expect("must succeed");
assert_eq!(payload, &buf[..]);
}
}