mkext4 0.0.3

Deterministic, streaming, pure-Rust ext4 image builder with a verification-grade reader
Documentation 
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

//! Kernel oracle: loop-mount a generated image and diff the mounted tree
//! against the declared namespace — types, modes, owners, timestamps,
//! nlink/hardlink identity, symlink targets, device numbers, xattrs,
//! content bytes, sparse holes, and htree lookups through the kernel.
//!
//! Requires root + Linux; gated on MKEXT4_MOUNT=1. CI builds the
//! test binary unprivileged and runs it under sudo.

#![cfg(target_os = "linux")]

use std::os::unix::fs::{FileTypeExt, MetadataExt, PermissionsExt};
use std::path::Path;
use std::process::Command;

use mkext4::sink::FileSink;
use mkext4::{FsBuilder, Meta, Options, SparseSeg, SpecialKind, ROOT};

mod common;
use common::{pattern_bytes, Pattern, EPOCH};

fn meta(mode: u16, uid: u32, gid: u32) -> Meta {
    Meta::new(mode, uid, gid, (EPOCH, 123_456_789))
}

fn sh(cmd: &str) -> Result<String, String> {
    let out = Command::new("sh").arg("-c").arg(cmd).output().unwrap();
    if out.status.success() {
        Ok(String::from_utf8_lossy(&out.stdout).into_owned())
    } else {
        Err(format!(
            "`{cmd}` failed: {}{}",
            String::from_utf8_lossy(&out.stdout),
            String::from_utf8_lossy(&out.stderr)
        ))
    }
}

#[test]
fn kernel_mount_oracle() {
    if std::env::var("MKEXT4_MOUNT").as_deref() != Ok("1") {
        eprintln!("SKIP: set MKEXT4_MOUNT=1 and run as root");
        return;
    }
    assert_eq!(effective_uid(), 0, "must run as root");

    let dir = Path::new(env!("CARGO_TARGET_TMPDIR"));
    std::fs::create_dir_all(dir).unwrap();
    let img = dir.join("mount_oracle.img");
    let mnt = dir.join("mnt");
    std::fs::create_dir_all(&mnt).unwrap();

    // --- build ------------------------------------------------------------
    let size = 1u64 << 30;
    let mut opts = Options::new(size, *b"mkext4-mounttest", EPOCH);
    opts.hash_seed = [1, 2, 3, 4];
    opts.label = Some("mnttest".into());
    opts.inodes = mkext4::InodeCount::Exact(150_000);
    let mut b = FsBuilder::new(opts).unwrap();

    let usr = b.mkdir(ROOT, "usr", meta(0o755, 0, 0)).unwrap();
    let f = b
        .file(usr, "file", meta(0o640, 1000, 1000), 100_000)
        .unwrap();
    b.hardlink(usr, "link", f).unwrap();
    b.file(usr, "empty", meta(0o600, 0, 0), 0).unwrap();
    b.symlink(ROOT, "fastlink", "usr/file", meta(0o777, 0, 0))
        .unwrap();
    b.symlink(ROOT, "slowlink", &"long/".repeat(30), meta(0o777, 0, 0))
        .unwrap();
    b.mknod(
        ROOT,
        "null",
        meta(0o666, 0, 0),
        SpecialKind::Char { major: 1, minor: 3 },
    )
    .unwrap();
    b.mknod(
        ROOT,
        "bigdev",
        meta(0o600, 0, 0),
        SpecialKind::Block {
            major: 259,
            minor: 70000,
        },
    )
    .unwrap();
    b.mknod(ROOT, "fifo", meta(0o644, 0, 0), SpecialKind::Fifo)
        .unwrap();
    let xf = b.file(ROOT, "xattrs", meta(0o644, 0, 0), 5).unwrap();
    b.set_xattr(xf, "user.small", b"hello").unwrap();
    b.set_xattr(xf, "user.big", &vec![0x41u8; 500]).unwrap();
    b.set_xattr(xf, "security.selinux", b"system_u:object_r:etc_t:s0")
        .unwrap();
    // 100k entries in one directory: the htree proof, looked up through
    // the kernel below.
    let htree = b.mkdir(ROOT, "htree", meta(0o755, 0, 0)).unwrap();
    for i in 0..100_000 {
        b.file(htree, &format!("entry_{i:06}_padpad"), meta(0o644, 0, 0), 0)
            .unwrap();
    }
    let sp = b
        .file_sparse(
            ROOT,
            "sparse",
            meta(0o644, 0, 0),
            &[
                SparseSeg::Data(4096),
                SparseSeg::Hole(64 << 20),
                SparseSeg::Data(3000),
            ],
        )
        .unwrap();

    let layout = b.seal().unwrap();
    let mut sink = FileSink::create(&img, layout.image_len()).unwrap();
    let mut w = layout.writer(&mut sink).unwrap();
    w.fill(f, &mut Pattern::new(100_000, 1)).unwrap();
    w.fill(xf, &mut Pattern::new(5, 2)).unwrap();
    w.fill(sp, &mut Pattern::new(4096 + 3000, 3)).unwrap();
    w.finish().unwrap();
    drop(sink);

    // --- mount ------------------------------------------------------------
    sh(&format!(
        "mount -o loop,ro {} {}",
        img.display(),
        mnt.display()
    ))
    .expect("loop mount");
    // Unmount even on panic.
    struct Umount(std::path::PathBuf);
    impl Drop for Umount {
        fn drop(&mut self) {
            let _ = sh(&format!("umount {}", self.0.display()));
        }
    }
    let _guard = Umount(mnt.clone());

    // --- diff ---------------------------------------------------------------
    // Regular file: content, mode, owner, mtime (ns), nlink.
    let p = mnt.join("usr/file");
    let m = std::fs::metadata(&p).unwrap();
    assert_eq!(std::fs::read(&p).unwrap(), pattern_bytes(100_000, 1));
    assert_eq!(m.permissions().mode() & 0o7777, 0o640);
    assert_eq!((m.uid(), m.gid()), (1000, 1000));
    assert_eq!(m.mtime(), EPOCH);
    assert_eq!(m.mtime_nsec(), 123_456_789);
    assert_eq!(m.nlink(), 2);
    assert_eq!(
        m.ino(),
        std::fs::metadata(mnt.join("usr/link")).unwrap().ino(),
        "hardlink shares the inode"
    );

    // Symlinks.
    assert_eq!(
        std::fs::read_link(mnt.join("fastlink")).unwrap(),
        Path::new("usr/file")
    );
    assert_eq!(
        std::fs::read_link(mnt.join("slowlink"))
            .unwrap()
            .as_os_str()
            .len(),
        150
    );

    // Devices (rdev encoding as the kernel sees it).
    let null = std::fs::metadata(mnt.join("null")).unwrap();
    assert!(null.file_type().is_char_device());
    assert_eq!(null.rdev(), makedev(1, 3));
    let bigdev = std::fs::metadata(mnt.join("bigdev")).unwrap();
    assert!(bigdev.file_type().is_block_device());
    assert_eq!(bigdev.rdev(), makedev(259, 70000));
    assert!(std::fs::metadata(mnt.join("fifo"))
        .unwrap()
        .file_type()
        .is_fifo());

    // xattrs through the kernel.
    let x = mnt.join("xattrs");
    assert_eq!(getfattr(&x, "user.small"), b"hello");
    assert_eq!(getfattr(&x, "user.big").len(), 500);
    assert_eq!(
        getfattr(&x, "security.selinux"),
        b"system_u:object_r:etc_t:s0"
    );

    // htree proof: kernel-side hashed lookups of a deterministic 1k-name
    // sample across the 100k-entry directory, plus a full readdir count.
    for i in (0..100_000).step_by(100) {
        let p = mnt.join(format!("htree/entry_{i:06}_padpad"));
        assert!(p.symlink_metadata().is_ok(), "{}", p.display());
    }
    assert_eq!(
        std::fs::read_dir(mnt.join("htree")).unwrap().count(),
        100_000
    );

    // Sparse: size, hole reads as zeros, block count reflects holes.
    let sp_path = mnt.join("sparse");
    let m = std::fs::metadata(&sp_path).unwrap();
    assert_eq!(m.len(), 4096 + (64 << 20) + 3000);
    assert!(m.blocks() < 100, "holes must not be allocated");
    let mut content = std::fs::read(&sp_path).unwrap();
    let want = pattern_bytes(4096 + 3000, 3);
    assert_eq!(&content[..4096], &want[..4096]);
    assert!(content[4096..4096 + (64 << 20)].iter().all(|&b| b == 0));
    assert_eq!(&content[4096 + (64 << 20)..], &want[4096..]);
    content.clear();

    // Whole-tree walk: every path readable, no kernel errors.
    fn walk(p: &Path) -> usize {
        let mut n = 0;
        for e in std::fs::read_dir(p).unwrap() {
            let e = e.unwrap();
            n += 1;
            if e.file_type().unwrap().is_dir() {
                n += walk(&e.path());
            }
        }
        n
    }
    assert!(walk(&mnt) > 100_000);

    let _ = std::fs::remove_file(&img);

    fn makedev(major: u64, minor: u64) -> u64 {
        // Linux dev_t encoding (glibc makedev).
        (major & 0xFFF) << 8 | (minor & 0xFF) | (minor & !0xFF) << 12
    }

    fn getfattr(path: &Path, name: &str) -> Vec<u8> {
        // getfattr --only-values prints the raw value.
        let out = Command::new("getfattr")
            .args(["--only-values", "--absolute-names", "-n", name])
            .arg(path)
            .output()
            .expect("getfattr (install attr)");
        assert!(
            out.status.success(),
            "getfattr {name}: {}",
            String::from_utf8_lossy(&out.stderr)
        );
        out.stdout
    }
}

/// Effective uid without a libc dependency: /proc/self/status "Uid:"
/// line, second field.
fn effective_uid() -> u32 {
    let status = std::fs::read_to_string("/proc/self/status").unwrap();
    status
        .lines()
        .find(|l| l.starts_with("Uid:"))
        .and_then(|l| l.split_whitespace().nth(2))
        .and_then(|s| s.parse().ok())
        .unwrap_or(u32::MAX)
}