cap_primitives/fs/
read_link.rs

1//! This defines `read_link`, the primary entrypoint to sandboxed symbolic link
2//! dereferencing.
3
4use crate::fs::{errors, read_link_impl};
5#[cfg(racy_asserts)]
6use crate::fs::{map_result, read_link_unchecked, stat, FollowSymlinks};
7use std::path::{Path, PathBuf};
8use std::{fs, io};
9
10/// Perform a `readlinkat`-like operation, ensuring that the resolution of the
11/// link path never escapes the directory tree rooted at `start`.
12#[cfg_attr(not(racy_asserts), allow(clippy::let_and_return))]
13#[inline]
14pub fn read_link_contents(start: &fs::File, path: &Path) -> io::Result<PathBuf> {
15    // Call the underlying implementation.
16    let result = read_link_impl(start, path);
17
18    #[cfg(racy_asserts)]
19    let unchecked = read_link_unchecked(start, path, PathBuf::new());
20
21    #[cfg(racy_asserts)]
22    check_read_link(start, path, &result, &unchecked);
23
24    result
25}
26
27/// Perform a `readlinkat`-like operation, ensuring that the resolution of the
28/// path never escapes the directory tree rooted at `start`, and also verifies
29/// that the link target is not absolute.
30#[cfg_attr(not(racy_asserts), allow(clippy::let_and_return))]
31#[inline]
32pub fn read_link(start: &fs::File, path: &Path) -> io::Result<PathBuf> {
33    // Call the underlying implementation.
34    let result = read_link_contents(start, path);
35
36    // Don't allow reading symlinks to absolute paths. This isn't strictly
37    // necessary to preserve the sandbox, since `open` will refuse to follow
38    // absolute paths in any case. However, it is useful to enforce this
39    // restriction to avoid leaking information about the host filesystem
40    // outside the sandbox.
41    if let Ok(path) = &result {
42        if path.has_root() {
43            return Err(errors::escape_attempt());
44        }
45    }
46
47    result
48}
49
50#[cfg(racy_asserts)]
51#[allow(clippy::enum_glob_use)]
52fn check_read_link(
53    start: &fs::File,
54    path: &Path,
55    result: &io::Result<PathBuf>,
56    unchecked: &io::Result<PathBuf>,
57) {
58    use io::ErrorKind::*;
59
60    match (map_result(result), map_result(unchecked)) {
61        (Ok(target), Ok(unchecked_target)) => {
62            assert_eq!(target, unchecked_target);
63        }
64
65        (Err((PermissionDenied, message)), _) => {
66            match map_result(&stat(start, path, FollowSymlinks::No)) {
67                Err((PermissionDenied, canon_message)) => {
68                    assert_eq!(message, canon_message);
69                }
70                _ => panic!("read_link failed where canonicalize succeeded"),
71            }
72        }
73
74        (Err((_kind, _message)), Err((_unchecked_kind, _unchecked_message))) => {
75            /* TODO: Check error messages.
76            assert_eq!(kind, unchecked_kind);
77            assert_eq!(message, unchecked_message);
78            */
79        }
80
81        other => panic!(
82            "unexpected result from read_link start='{:?}', path='{}':\n{:#?}",
83            start,
84            path.display(),
85            other,
86        ),
87    }
88}
89
90#[cfg(not(windows))]
91#[test]
92fn test_read_link_contents() {
93    use io_lifetimes::AsFilelike;
94    let td = cap_tempfile::tempdir(cap_tempfile::ambient_authority()).unwrap();
95    let td_view = &td.as_filelike_view::<std::fs::File>();
96    let valid = [
97        "relative/path",
98        "/some/absolute/path",
99        "/",
100        "../",
101        "basepath",
102    ];
103    for case in valid {
104        let linkname = Path::new("linkname");
105        crate::fs::symlink_contents(case, td_view, linkname).unwrap();
106        let contents = crate::fs::read_link_contents(td_view, linkname).unwrap();
107        assert_eq!(contents.to_str().unwrap(), case);
108        crate::fs::remove_file(td_view, linkname).unwrap();
109    }
110}
cap_primitives/fs/read_link.rs

cap_primitives/fs/
read_link.rs
