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fix(pack): harden asset archive extraction #306

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143 changes: 136 additions & 7 deletions crates/smolvm-pack/src/assets.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@

use std::fs::{self, File};
use std::io::{BufWriter, Read, Seek, SeekFrom, Write};
use std::path::{Path, PathBuf};
use std::path::{Component, Path, PathBuf};

use crate::format::{AssetEntry, AssetInventory, LayerEntry};
use crate::{PackError, Result};
Expand Down Expand Up @@ -585,6 +585,56 @@ fn find_last_data_byte(file: &mut File, logical_size: u64) -> std::io::Result<u6
Ok(0) // Entire file is zeros
}

fn validate_archive_path(path: &Path) -> Result<()> {
if path.components().any(|component| {
matches!(
component,
Component::ParentDir | Component::RootDir | Component::Prefix(_)
)
}) {
return Err(PackError::Tar(format!(
"archive entry escapes output directory: {}",
path.display()
)));
}

Ok(())
}

fn safe_unpack_archive<R: Read>(archive: &mut tar::Archive<R>, output_dir: &Path) -> Result<()> {
for entry in archive
.entries()
.map_err(|e| PackError::Tar(e.to_string()))?
{
let mut entry = entry.map_err(|e| PackError::Tar(e.to_string()))?;
let path = entry
.path()
.map_err(|e| PackError::Tar(e.to_string()))?
.into_owned();
validate_archive_path(&path)?;

let entry_type = entry.header().entry_type();
if entry_type.is_symlink() || entry_type.is_hard_link() {
return Err(PackError::Tar(format!(
"archive links are not allowed in assets: {}",
path.display()
)));
}

if !entry
.unpack_in(output_dir)
.map_err(|e| PackError::Tar(e.to_string()))?
{
return Err(PackError::Tar(format!(
"archive entry escapes output directory: {}",
path.display()
)));
}
}

Ok(())
}

/// Decompress a zstd-compressed assets blob.
pub fn decompress_assets(compressed: &[u8], output_dir: &Path) -> Result<()> {
fs::create_dir_all(output_dir)?;
Expand All @@ -593,9 +643,7 @@ pub fn decompress_assets(compressed: &[u8], output_dir: &Path) -> Result<()> {
.map_err(|e| PackError::Compression(e.to_string()))?;
let mut archive = tar::Archive::new(decoder);

archive
.unpack(output_dir)
.map_err(|e| PackError::Tar(e.to_string()))?;
safe_unpack_archive(&mut archive, output_dir)?;

Ok(())
}
Expand All @@ -609,9 +657,7 @@ pub fn decompress_assets_from_file(compressed_path: &Path, output_dir: &Path) ->
zstd::stream::Decoder::new(file).map_err(|e| PackError::Compression(e.to_string()))?;
let mut archive = tar::Archive::new(decoder);

archive
.unpack(output_dir)
.map_err(|e| PackError::Tar(e.to_string()))?;
safe_unpack_archive(&mut archive, output_dir)?;

Ok(())
}
Expand Down Expand Up @@ -732,6 +778,89 @@ mod tests {
assert_eq!(dst_data[256], 0x00); // interior zero is preserved
}

#[test]
fn test_decompress_assets_extracts_regular_files() {
let mut tar_data = Vec::new();
{
let mut builder = tar::Builder::new(&mut tar_data);
let mut header = tar::Header::new_gnu();
let content = b"hello assets";
header.set_path("nested/asset.txt").unwrap();
header.set_size(content.len() as u64);
header.set_cksum();
builder.append(&header, &content[..]).unwrap();
builder.finish().unwrap();
}

let compressed = zstd::stream::encode_all(tar_data.as_slice(), ZSTD_LEVEL).unwrap();
let temp_dir = tempfile::tempdir().unwrap();
decompress_assets(&compressed, temp_dir.path()).unwrap();

assert_eq!(
fs::read_to_string(temp_dir.path().join("nested/asset.txt")).unwrap(),
"hello assets"
);
}

#[test]
fn test_decompress_assets_rejects_parent_paths() {
let mut tar_data = Vec::new();
{
let content = b"escape";
let mut raw_header = [0u8; 512];
raw_header[..14].copy_from_slice(b"../escape.txt\0");
raw_header[100..108].copy_from_slice(b"0000644\0");
raw_header[108..116].copy_from_slice(b"0000000\0");
raw_header[116..124].copy_from_slice(b"0000000\0");
raw_header[124..136].copy_from_slice(format!("{:011o}\0", content.len()).as_bytes());
raw_header[136..148].copy_from_slice(b"00000000000\0");
raw_header[148..156].fill(b' ');
raw_header[156] = b'0';
raw_header[257..263].copy_from_slice(b"ustar\0");
raw_header[263..265].copy_from_slice(b"00");
let checksum: u32 = raw_header.iter().map(|byte| u32::from(*byte)).sum();
raw_header[148..156].copy_from_slice(format!("{:06o}\0 ", checksum).as_bytes());
tar_data.extend_from_slice(&raw_header);
tar_data.extend_from_slice(content);
tar_data.resize(tar_data.len().next_multiple_of(512), 0);
tar_data.extend_from_slice(&[0u8; 1024]);
}

let compressed = zstd::stream::encode_all(tar_data.as_slice(), ZSTD_LEVEL).unwrap();
let temp_dir = tempfile::tempdir().unwrap();
let result = decompress_assets(&compressed, temp_dir.path());

assert!(
matches!(result, Err(PackError::Tar(message)) if message.contains("escapes output directory"))
);
assert!(!temp_dir.path().join("../escape.txt").exists());
}

#[test]
fn test_decompress_assets_rejects_links() {
let mut tar_data = Vec::new();
{
let mut builder = tar::Builder::new(&mut tar_data);
let mut header = tar::Header::new_gnu();
header.set_entry_type(tar::EntryType::Symlink);
header.set_path("link").unwrap();
header.set_link_name("/etc/passwd").unwrap();
header.set_size(0);
header.set_cksum();
builder.append(&header, std::io::empty()).unwrap();
builder.finish().unwrap();
}

let compressed = zstd::stream::encode_all(tar_data.as_slice(), ZSTD_LEVEL).unwrap();
let temp_dir = tempfile::tempdir().unwrap();
let result = decompress_assets(&compressed, temp_dir.path());

assert!(
matches!(result, Err(PackError::Tar(message)) if message.contains("links are not allowed"))
);
assert!(!temp_dir.path().join("link").exists());
}

#[test]
fn test_crc32_basic() {
let data = b"hello world";
Expand Down