feat(storage): encrypted areas layer (home, system, data/<id>) over any FS; locked until key; plaintext refused; tamper/truncation detected; tests on memory + real ext4

crates/servers/storage-server/src/tests/encrypted.rs

@@ -0,0 +1,275 @@
+extern crate std;
+
+use crate::encrypted::{Encrypted, area_of};
+use crate::filesystem::{DirEntry, FileHandle, FileName, FileSystem};
+use std::collections::BTreeMap;
+use std::string::{String, ToString};
+use std::vec;
+use std::vec::Vec;
+
+/// Files in memory, with positions: what the layer sits on in tests.
+#[derive(Default)]
+struct Memory {
+    files: BTreeMap<String, Vec<u8>>,
+    dirs: Vec<String>,
+    open: BTreeMap<u16, (String, usize)>,
+    next: u16,
+}
+
+fn key(path: &[u8]) -> String {
+    String::from_utf8_lossy(path.strip_prefix(b"/").unwrap_or(path)).into_owned()
+}
+
+impl Memory {
+    fn handle(&mut self, path: String) -> FileHandle {
+        self.next = (self.next + 1) % 16;
+        self.open.insert(self.next, (path, 0));
+        FileHandle::new(self.next)
+    }
+}
+
+impl FileSystem for Memory {
+    fn open(&mut self, path: &[u8]) -> Option<FileHandle> {
+        let k = key(path);
+        self.files.contains_key(&k).then(|| self.handle(k))
+    }
+    fn create(&mut self, path: &[u8]) -> Option<FileHandle> {
+        let k = key(path);
+        if self.files.contains_key(&k) {
+            return None;
+        }
+        self.files.insert(k.clone(), Vec::new());
+        Some(self.handle(k))
+    }
+    fn read(&mut self, h: FileHandle, buf: &mut [u8]) -> Option<usize> {
+        let (path, pos) = self.open.get_mut(&h.raw())?;
+        let data = &self.files[path.as_str()];
+        let n = buf.len().min(data.len().saturating_sub(*pos));
+        buf[..n].copy_from_slice(&data[*pos..*pos + n]);
+        *pos += n;
+        Some(n)
+    }
+    fn write(&mut self, h: FileHandle, buf: &[u8]) -> Option<usize> {
+        let (path, pos) = self.open.get_mut(&h.raw())?;
+        let data = self.files.get_mut(path.as_str())?;
+        if data.len() < *pos + buf.len() {
+            data.resize(*pos + buf.len(), 0);
+        }
+        data[*pos..*pos + buf.len()].copy_from_slice(buf);
+        *pos += buf.len();
+        Some(buf.len())
+    }
+    fn seek(&mut self, h: FileHandle, offset: usize) -> bool {
+        let Some((path, pos)) = self.open.get_mut(&h.raw()) else { return false };
+        if offset > self.files[path.as_str()].len() {
+            return false;
+        }
+        *pos = offset;
+        true
+    }
+    fn close(&mut self, h: FileHandle) {
+        self.open.remove(&h.raw());
+    }
+    fn file_size(&mut self, h: FileHandle) -> Option<usize> {
+        let (path, _) = self.open.get(&h.raw())?;
+        Some(self.files[path.as_str()].len())
+    }
+    fn list_dir(&mut self, path: &[u8], entries: &mut [DirEntry]) -> Option<usize> {
+        let prefix = std::format!("{}/", key(path));
+        let mut n = 0;
+        for (name, data) in self.files.iter().filter(|(k, _)| k.starts_with(&prefix)) {
+            entries[n] = DirEntry { name: FileName::from_bytes(name[prefix.len()..].as_bytes()), size: data.len(), is_dir: false };
+            n += 1;
+        }
+        Some(n)
+    }
+    fn delete(&mut self, path: &[u8]) -> bool {
+        self.files.remove(&key(path)).is_some()
+    }
+    fn mkdir(&mut self, path: &[u8]) -> bool {
+        self.dirs.push(key(path));
+        true
+    }
+    fn rmdir(&mut self, path: &[u8]) -> bool {
+        let k = key(path);
+        let before = self.dirs.len();
+        self.dirs.retain(|d| *d != k);
+        self.dirs.len() < before
+    }
+}
+
+const MASTER: [u8; 32] = [9; 32];
+
+fn unlocked() -> Encrypted<Memory> {
+    let mut fs = Encrypted::new(Memory::default());
+    fs.unlock(&MASTER, &[3; 32]);
+    fs
+}
+
+fn put(fs: &mut impl FileSystem, path: &[u8], data: &[u8]) {
+    let h = fs.create(path).expect("create");
+    assert_eq!(fs.write(h, data), Some(data.len()));
+    fs.close(h);
+}
+
+fn get(fs: &mut impl FileSystem, path: &[u8]) -> Option<Vec<u8>> {
+    let h = fs.open(path)?;
+    let size = fs.file_size(h)?;
+    let mut out = vec![0u8; size + 10];
+    let n = fs.read(h, &mut out);
+    fs.close(h);
+    out.truncate(n?);
+    Some(out)
+}
+
+fn on_disk(fs: &Encrypted<Memory>, path: &str) -> Vec<u8> {
+    fs.inner().files[path].clone()
+}
+
+#[test]
+fn areas_are_told_by_path() {
+    for (p, a) in [
+        (&b"home/readme.txt"[..], "sealed"),
+        (b"/home", "sealed"),
+        (b"system/permissions/kos.snake", "sealed"),
+        (b"data/kos.notes/a", "sealed"),
+        (b"data/kos.notes", "neither"),
+        (b"data", "neither"),
+        (b"data/", "neither"),
+        (b"bin/shell", "plain"),
+        (b"apps/kos.cat/cat", "plain"),
+        (b"factory/home/readme.txt", "plain"),
+        (b"homework/x", "plain"),
+        (b"selftest.txt", "plain"),
+    ] {
+        assert_eq!(area_of(p), a, "{}", String::from_utf8_lossy(p));
+    }
+}
+
+#[test]
+fn sealed_files_read_back_and_are_noise_on_disk() {
+    let mut fs = unlocked();
+    let text = b"Dear diary, nobody else may read this.";
+    put(&mut fs, b"home/diary.txt", text);
+    assert_eq!(get(&mut fs, b"home/diary.txt").unwrap(), text);
+    let disk = on_disk(&fs, "home/diary.txt");
+    assert!(disk.starts_with(b"KOSFILE1"));
+    assert!(!disk.windows(5).any(|w| w == b"diary"), "the words are not on the disk");
+    assert_eq!(disk.len(), filecrypt::disk_len(text.len()));
+}
+
+#[test]
+fn plaintext_areas_stay_plaintext() {
+    let mut fs = unlocked();
+    put(&mut fs, b"bin/tool", b"\x7fELF");
+    assert_eq!(on_disk(&fs, "bin/tool"), b"\x7fELF");
+    assert_eq!(get(&mut fs, b"bin/tool").unwrap(), b"\x7fELF");
+}
+
+#[test]
+fn big_files_and_writes_across_chunks_round_trip() {
+    let mut fs = unlocked();
+    let big: Vec<u8> = (0..3 * filecrypt::PLAIN_CHUNK + 123).map(|i| (i % 251) as u8).collect();
+    put(&mut fs, b"data/kos.notes/big", &big);
+    assert_eq!(get(&mut fs, b"data/kos.notes/big").unwrap(), big);
+    // Overwrite a stretch spanning two chunks in the middle.
+    let h = fs.open(b"data/kos.notes/big").unwrap();
+    let at = filecrypt::PLAIN_CHUNK - 10;
+    assert!(fs.seek(h, at));
+    assert_eq!(fs.write(h, &[0xAA; 30]), Some(30));
+    fs.close(h);
+    let mut expect = big.clone();
+    expect[at..at + 30].fill(0xAA);
+    assert_eq!(get(&mut fs, b"data/kos.notes/big").unwrap(), expect);
+    // Grow exactly from a chunk boundary: the old last chunk stops being last.
+    let mut fs = unlocked();
+    let full = vec![7u8; filecrypt::PLAIN_CHUNK];
+    put(&mut fs, b"home/f", &full);
+    let h = fs.open(b"home/f").unwrap();
+    assert!(fs.seek(h, filecrypt::PLAIN_CHUNK));
+    assert_eq!(fs.write(h, b"more"), Some(4));
+    fs.close(h);
+    let mut expect = full.clone();
+    expect.extend_from_slice(b"more");
+    assert_eq!(get(&mut fs, b"home/f").unwrap(), expect);
+}
+
+#[test]
+fn one_app_cannot_read_anothers_file_even_moved_into_its_folder() {
+    let mut fs = unlocked();
+    put(&mut fs, b"data/kos.notes/secret", b"notes only");
+    let stolen = on_disk(&fs, "data/kos.notes/secret");
+    fs.inner_mut_for_test().files.insert("data/kos.chat/secret".to_string(), stolen);
+    let h = fs.open(b"data/kos.chat/secret").expect("it looks like a sealed file");
+    let mut out = [0u8; 64];
+    assert_eq!(fs.read(h, &mut out), None, "but it opens only under kos.notes' key");
+}
+
+#[test]
+fn locked_the_areas_refuse_everything() {
+    let mut fs = unlocked();
+    put(&mut fs, b"home/x", b"y");
+    let mut locked = Encrypted::new(fs.into_inner());
+    assert!(locked.open(b"home/x").is_none());
+    assert!(locked.create(b"home/z").is_none());
+    assert!(!locked.delete(b"home/x"));
+    assert!(!locked.mkdir(b"data/kos.notes"));
+    assert!(locked.list_dir(b"home", &mut [DirEntry::empty(); 4]).is_none());
+    assert!(locked.open(b"bin/anything").is_none(), "(absent) but plaintext areas are not refused");
+    // Another master key (a wiped and re-set-up device) reads noise.
+    let mut other = Encrypted::new(locked.into_inner());
+    other.unlock(&[1; 32], &[2; 32]);
+    let h = other.open(b"home/x").unwrap();
+    assert_eq!(other.read(h, &mut [0u8; 8]), None);
+}
+
+#[test]
+fn plaintext_planted_in_an_encrypted_area_is_refused() {
+    let mut fs = unlocked();
+    fs.inner_mut_for_test().files.insert("system/permissions/kos.evil".to_string(), b"[decision]\ngranted = [\"network\"]\n".to_vec());
+    assert!(fs.open(b"system/permissions/kos.evil").is_none());
+}
+
+#[test]
+fn tampering_and_truncation_are_caught() {
+    let mut fs = unlocked();
+    let data = vec![5u8; 2 * filecrypt::PLAIN_CHUNK + 50];
+    put(&mut fs, b"home/t", &data);
+    let good = on_disk(&fs, "home/t");
+    // One flipped byte.
+    let mut bent = good.clone();
+    bent[100] ^= 1;
+    fs.inner_mut_for_test().files.insert("home/t".to_string(), bent);
+    assert_eq!(get(&mut fs, b"home/t"), None);
+    // Cut at a chunk boundary: the remaining last chunk was not sealed as last.
+    let cut = good[..filecrypt::chunk_offset(2)].to_vec();
+    fs.inner_mut_for_test().files.insert("home/t".to_string(), cut);
+    assert_eq!(get(&mut fs, b"home/t"), None);
+    // Chunks swapped.
+    let (a, b) = (filecrypt::chunk_offset(0), filecrypt::chunk_offset(1));
+    let mut swapped = good.clone();
+    swapped[a..b].copy_from_slice(&good[b..b + filecrypt::CHUNK]);
+    swapped[b..b + filecrypt::CHUNK].copy_from_slice(&good[a..b]);
+    fs.inner_mut_for_test().files.insert("home/t".to_string(), swapped);
+    assert_eq!(get(&mut fs, b"home/t"), None);
+}
+
+#[test]
+fn listings_show_what_files_hold() {
+    let mut fs = unlocked();
+    put(&mut fs, b"home/a", b"12345");
+    let mut entries = [DirEntry::empty(); 4];
+    let n = fs.list_dir(b"home", &mut entries).unwrap();
+    assert_eq!((n, entries[0].size), (1, 5));
+}
+
+#[test]
+fn files_cannot_live_loose_in_data() {
+    let mut fs = unlocked();
+    assert!(fs.create(b"data/loose").is_none());
+    assert!(fs.mkdir(b"data/kos.notes"), "an app's folder is fine");
+    let mut entries = [DirEntry::empty(); 2];
+    put(&mut fs, b"data/kos.notes/a", b"xyz");
+    let n = fs.list_dir(b"data/kos.notes", &mut entries).unwrap();
+    assert_eq!((n, entries[0].size), (1, 3), "listing the folder shows what its files hold");
+}