Cargo.lock

@@ -88,6 +88,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d2f6c7dbe95a6ed67ad9f18e57daf93a2f034c524b99fd2b76d18fdfeb6660aa"
 dependencies = [
  "hybrid-array",
+ "zeroize",
 ]
 
 [[package]]
@@ -121,6 +122,7 @@ dependencies = [
  "cfg-if",
  "cipher",
  "cpufeatures",
+ "zeroize",
 ]
 
 [[package]]
@@ -133,6 +135,7 @@ dependencies = [
  "chacha20",
  "cipher",
  "poly1305",
+ "zeroize",
 ]
 
 [[package]]
@@ -277,6 +280,7 @@ dependencies = [
  "block-buffer",
  "crypto-common",
  "ctutils",
+ "zeroize",
 ]
 
 [[package]]

Cargo.toml

@@ -11,11 +11,11 @@ publish = false
 
 [dependencies]
 argon2 = { version = "0.6", default-features = false, features = ["alloc", "zeroize"] }
-chacha20poly1305 = { version = "0.11", default-features = false, features = ["alloc"] }
+chacha20poly1305 = { version = "0.11", default-features = false, features = ["alloc", "zeroize"] }
 hkdf = "0.13"
-hmac = "0.13"
-sha2 = { version = "0.11", default-features = false }
-sha3 = { version = "0.11", default-features = false }
+hmac = { version = "0.13", features = ["zeroize"] }
+sha2 = { version = "0.11", default-features = false, features = ["zeroize"] }
+sha3 = { version = "0.11", default-features = false, features = ["zeroize"] }
 ml-kem = { version = "0.3.2", features = ["zeroize", "hazmat"] }
 zeroize = { version = "1.9", features = ["derive", "serde"] }
 getrandom = "0.4"

SECURITY.md

@@ -63,7 +63,8 @@ None of this is erasure from physical memory.
 `VAULT_PASSPHRASE` and `VAULT_DECOY_PASSPHRASE` removed from its environment,
 no secret in its arguments, its working directory `/` and standard error
 closed. It hands over the 34-byte suite ID and seed through a pipe. Before
-reading it, the agent:
+reading it (straight from the pipe into the locked page, with no
+intermediate buffer), the agent:
 
 1. sets the core-dump size limit to zero;
 2. on Linux, sets `PR_SET_DUMPABLE` to 0 (no core dumps, no same-user
@@ -108,16 +109,25 @@ for the passphrase.
   A failure after a record is already in place never deletes its objects.
   Windows has no directory fsync through the APIs used; NTFS journals
   metadata.
+- `migrate` checks an original is still the file it stored (device, inode,
+  size, time; on Windows only size and time) and then deletes it by name; a
+  replacement in the instant between the check and the deletion is not
+  excluded. Paths inside the vault directory are refused outright.
+- A filesystem with neither `RENAME_NOREPLACE` nor hard links (some FUSE
+  mounts, FAT) cannot publish without risking a replace, so `get` fails
+  there with a message saying so rather than fall back.
 - The vault lock uses the same POSIX `fcntl` locks as the Go version, so
   mixed Go and Rust processes exclude each other. Only a read-only
   filesystem lets a reader proceed without the lock.
 
 ## Plaintext on disk
 
-- `vault add URL` and `vault mirror` stream non-HTML downloads to a private
-  (0600) temporary file in `$TMPDIR` before storing them, because the size
-  must be known first; it is removed on every normal path, including
-  errors. HTML and CSS are rewritten in memory. `vault absorb` stores tar
+- `vault add URL` and `vault mirror` stream non-HTML downloads to a 0600
+  temporary file in `$TMPDIR` before storing them, because the size must be
+  known first. On Unix the file is unlinked as soon as it is created, so it
+  has no name and disappears even if vault is killed; on other systems it
+  is a named file removed on every normal path, including errors. HTML and
+  CSS are rewritten in memory. `vault absorb` stores tar
   entries straight from the stream with no temporary file.
 - `vault get` writes plaintext where you ask; `vault migrate` deletes the
   originals with `unlink`, which is not secure deletion.

docs/MIGRATION.md

@@ -23,6 +23,14 @@ Safety and correctness:
   use, see `SECURITY.md`.)
 - **Extracted files are synced** to disk before they appear under their
   name, and their directory afterwards.
+- **`get` needs an atomic no-replace primitive.** On a filesystem with
+  neither `RENAME_NOREPLACE` nor hard links (some FUSE mounts, FAT) it fails
+  with a message saying so, where Go would rename.
+- **`add`/`migrate` refuse paths inside the vault directory** (Go refused
+  only the directory itself; `migrate store/records` would have deleted the
+  vault's records).
+- **`absorb` refuses GNU sparse files** (Go expanded them), and honours PAX
+  size records as Go does.
 - **A source file that changes while being added is not stored.** If it
   grows, shrinks, is modified or replaced during `add`/`migrate`, the
   command fails and nothing is stored. Go stored whatever it read (for a

src/absorb.rs

@@ -52,10 +52,14 @@ pub fn absorb(
         };
         let name = join(&[dest, &rel]);
         let name = VaultName::new(&name).ok_or_else(|| Error::new(format!("invalid vault path {name:?}")))?;
-        let size = entry
-            .header()
-            .size()
-            .map_err(|e| Error::new(format!("reading archive: {}", crate::util::io_reason(&e))))?;
+        // The entry's size, with a PAX "size" override applied, as Go's
+        // hdr.Size; the fixed header field alone would truncate files that
+        // Go's archive/tar writes for sizes past 8 GiB.
+        let size = entry.size();
+        if is_gnu_sparse(&mut entry) {
+            eprintln!("skipping {shown}: sparse files are not supported");
+            continue;
+        }
         let mode = entry.header().mode().unwrap_or(0) & 0o777;
         let mtime = mtime(&mut entry)?;
         match store.add_reader(cat, &mut entry, size, mode, mtime, &name) {
@@ -84,6 +88,18 @@ pub fn safe_name(name: &str) -> Option<String> {
     Some(n)
 }
 
+/// A PAX-format GNU sparse file, whose data is an encoded map, not the
+/// file's bytes.
+fn is_gnu_sparse<R: Read>(entry: &mut tar::Entry<R>) -> bool {
+    if entry.header().entry_type() == tar::EntryType::GNUSparse {
+        return true;
+    }
+    match entry.pax_extensions() {
+        Ok(Some(exts)) => exts.flatten().any(|e| e.key_bytes().starts_with(b"GNU.sparse.")),
+        _ => false,
+    }
+}
+
 /// The entry's modification time: the PAX `mtime` (with its fraction) if
 /// present, else the header's whole seconds.
 fn mtime<R: Read>(entry: &mut tar::Entry<R>) -> Result<Instant> {
@@ -236,6 +252,42 @@ mod tests {
         assert_eq!(s.catalogue().unwrap().len(), before);
     }
 
+    /// A PAX "size" record overrides the header's size field, as Go writes
+    /// for files over 8 GiB; the whole body must be stored.
+    #[test]
+    fn pax_size_override() {
+        let (d, s) = store("absorb-pax");
+        let mut t = Vec::new();
+        let rec = |k: &str, v: &str| {
+            let body = format!(" {k}={v}\n");
+            let mut n = body.len() + 1;
+            while format!("{n}{body}").len() != n {
+                n += 1;
+            }
+            format!("{n}{body}")
+        };
+        let pax = rec("size", "11");
+        let mut h = header("PaxHeaders/big", tar::EntryType::XHeader, pax.len() as u64, 0o644, 0);
+        h.set_cksum();
+        t.extend_from_slice(h.as_bytes());
+        let mut p = pax.into_bytes();
+        p.resize(p.len().div_ceil(512) * 512, 0);
+        t.extend_from_slice(&p);
+        let h = header("big.bin", tar::EntryType::Regular, 0, 0o644, 0);
+        t.extend_from_slice(h.as_bytes());
+        let mut body = b"hello world".to_vec();
+        body.resize(512, 0);
+        t.extend_from_slice(&body);
+        t.extend_from_slice(&[0u8; 1024]);
+        let mut cat = s.catalogue().unwrap();
+        absorb(&s, &mut cat, &t[..], "", &mut |_, _| {}).unwrap();
+        let r = cat.current("big.bin").unwrap();
+        assert_eq!(r.size, 11);
+        let dir = crate::platform::fs::Dir::open(&d.0).unwrap();
+        s.extract(r, &dir, std::ffi::OsStr::new("o")).unwrap();
+        assert_eq!(std::fs::read(d.0.join("o")).unwrap(), b"hello world");
+    }
+
     #[test]
     fn names_and_times() {
         // As in Go, only names that would climb out are refused; others are

src/agent.rs

@@ -226,6 +226,19 @@ mod imp {
         }
     }
 
+    fn read_fd0(buf: &mut [u8]) -> std::io::Result<()> {
+        let mut done = 0;
+        while done < buf.len() {
+            match rustix::io::read(rustix::stdio::stdin(), &mut buf[done..]) {
+                Ok(0) => return Err(std::io::ErrorKind::UnexpectedEof.into()),
+                Ok(n) => done += n,
+                Err(rustix::io::Errno::INTR) => {}
+                Err(e) => return Err(e.into()),
+            }
+        }
+        Ok(())
+    }
+
     /// The agent process. Returns when it expires or is told to quit.
     pub fn run(sock: &Path, ttl: &str, mode: &str) {
         let mut out = std::io::stdout();
@@ -249,7 +262,9 @@ mod imp {
             Ok(b) => b,
             Err(e) => return report(&mut out, &e.to_string()),
         };
-        if std::io::stdin().lock().read_exact(secret.as_mut_slice()).is_err() {
+        // Read straight from fd 0 into the locked page: std's buffered
+        // stdin would leave a copy in ordinary heap memory.
+        if read_fd0(secret.as_mut_slice()).is_err() {
             return report(&mut out, "no key received");
         }
         {
@@ -258,8 +273,12 @@ mod imp {
                 return report(&mut out, &e);
             }
         }
-        // A socket left by an agent that died stops bind; start has already
-        // stopped any live one.
+        // A socket left by an agent that died stops bind. Remove it only if
+        // nothing answers on it, so a concurrent unlock's live agent is not
+        // cut off from `vault lock`.
+        if UnixStream::connect(sock).is_ok() {
+            return report(&mut out, "another agent is already running for this key");
+        }
         let _ = std::fs::remove_file(sock);
         let l = match UnixListener::bind(sock) {
             Ok(l) => l,

src/cli.rs

@@ -477,8 +477,14 @@ fn run(cmd: &str, args: &[String]) -> Result<i32> {
             }
             let (s, _lock) = ctx.open(true)?;
             let mut cat = s.catalogue()?;
-            // Never ingest, or delete, the vault or its key.
-            let skip: Vec<FileId> = [ctx.vault_dir()?, ctx.key()?].iter().filter_map(|p| FileId::of(p, true)).collect();
+            // Never ingest, or delete, the vault, anything inside it, or its key.
+            let vault_dir = ctx.vault_dir()?;
+            if let (Ok(v), Ok(src)) = (std::fs::canonicalize(&vault_dir), std::fs::canonicalize(&pos[0])) {
+                if src != v && src.starts_with(&v) {
+                    crate::bail!("{} is inside the vault", pos[0]);
+                }
+            }
+            let skip: Vec<FileId> = [vault_dir, ctx.key()?].iter().filter_map(|p| FileId::of(p, true)).collect();
             let yes = ctx.flags.yes;
             add_path(&s, &mut cat, Path::new(&pos[0]), &dest, migrate, &skip, &mut |names| {
                 yes || confirm_overwrite(names)

src/crypto/stream.rs

@@ -122,6 +122,8 @@ pub struct StreamWriter<W: Write> {
     dst: Option<W>,
     buf: Vec<u8>,
     index: u64,
+    /// Set by any failure: like Go's sticky error, every later call fails.
+    failed: bool,
 }
 
 impl<W: Write> StreamWriter<W> {
@@ -131,6 +133,7 @@ impl<W: Write> StreamWriter<W> {
             dst: Some(dst),
             buf: Vec::with_capacity(ENC_CHUNK_SIZE),
             index: 0,
+            failed: false,
         }
     }
 
@@ -141,7 +144,24 @@ impl<W: Write> StreamWriter<W> {
         w
     }
 
+    fn check(&self) -> io::Result<()> {
+        if self.failed {
+            Err(io::Error::other("encrypted stream writer already failed"))
+        } else {
+            Ok(())
+        }
+    }
+
     fn flush_chunk(&mut self, last: bool) -> io::Result<()> {
+        let r = self.seal_and_write(last);
+        if r.is_err() {
+            self.failed = true;
+            self.buf.zeroize();
+        }
+        r
+    }
+
+    fn seal_and_write(&mut self, last: bool) -> io::Result<()> {
         let n = self.buf.len();
         self.buf.resize(n + TAG_SIZE, 0);
         self.cipher.seal(self.index, last, &mut self.buf);
@@ -152,6 +172,7 @@ impl<W: Write> StreamWriter<W> {
     }
 
     pub fn finish(mut self) -> io::Result<W> {
+        self.check()?;
         self.flush_chunk(true)?;
         Ok(self.dst.take().expect("writer in use"))
     }
@@ -159,6 +180,7 @@ impl<W: Write> StreamWriter<W> {
 
 impl<W: Write> Write for StreamWriter<W> {
     fn write(&mut self, mut p: &[u8]) -> io::Result<usize> {
+        self.check()?;
         let total = p.len();
         while !p.is_empty() {
             let take = p.len().min(CHUNK_SIZE - self.buf.len());
@@ -174,6 +196,7 @@ impl<W: Write> Write for StreamWriter<W> {
     }
 
     fn flush(&mut self) -> io::Result<()> {
+        self.check()?;
         self.dst.as_mut().expect("writer in use").flush()
     }
 }
@@ -287,8 +310,11 @@ impl<R: Read> StreamReader<R> {
             }
             if raw.len() < ENC_CHUNK_SIZE {
                 // A short first chunk is final; empty is the empty file.
-                let p = self.open(raw, true)?;
-                expect_eof(&mut self.src)?;
+                let mut p = self.open(raw, true)?;
+                if let Err(e) = expect_eof(&mut self.src) {
+                    p.zeroize();
+                    return Err(e);
+                }
                 self.deliver(p);
                 self.done = true;
                 return Ok(());
@@ -307,9 +333,19 @@ impl<R: Read> StreamReader<R> {
             if next.len() == TAG_SIZE {
                 return Err(StreamError::EmptyLastChunk.into());
             }
-            let p = self.open(pending, false)?;
-            let q = self.open(next, true)?;
-            expect_eof(&mut self.src)?;
+            let mut p = self.open(pending, false)?;
+            let mut q = match self.open(next, true) {
+                Ok(q) => q,
+                Err(e) => {
+                    p.zeroize();
+                    return Err(e);
+                }
+            };
+            if let Err(e) = expect_eof(&mut self.src) {
+                p.zeroize();
+                q.zeroize();
+                return Err(e);
+            }
             self.deliver(p);
             self.queued = Some(q);
             self.done = true;
@@ -514,7 +550,8 @@ impl<'a, S: ReadAt + ?Sized> StreamReaderAt<'a, S> {
             ));
         }
         let mut n = 0;
-        let mut chunk = vec![0u8; ENC_CHUNK_SIZE];
+        // Cleared on every exit, early returns included.
+        let mut chunk = zeroize::Zeroizing::new(vec![0u8; ENC_CHUNK_SIZE]);
         let mut cache = self.cache.lock().unwrap_or_else(|e| e.into_inner());
         while n < p.len() && off < self.size {
             let idx = off / CHUNK_SIZE as u64;
@@ -538,7 +575,7 @@ impl<'a, S: ReadAt + ?Sized> StreamReaderAt<'a, S> {
             n += take;
             off += take as u64;
         }
-        chunk.zeroize();
+
         Ok(n)
     }
 }
@@ -750,6 +787,26 @@ pub(crate) mod tests {
         assert!(encrypted_chunk_count(ENC_CHUNK_SIZE as u64 + 16).is_err());
     }
 
+    /// After a failed write the writer refuses everything, as Go's does,
+    /// instead of growing past a chunk.
+    #[test]
+    fn writer_failure_is_sticky() {
+        struct Full;
+        impl Write for Full {
+            fn write(&mut self, _: &[u8]) -> io::Result<usize> {
+                Err(io::Error::other("disk full"))
+            }
+            fn flush(&mut self) -> io::Result<()> {
+                Ok(())
+            }
+        }
+        let mut w = StreamWriter::new(&[1u8; 32], Full);
+        assert!(w.write_all(&pt(CHUNK_SIZE + 1)).is_err());
+        assert!(w.write_all(&pt(10)).is_err());
+        assert!(w.flush().is_err());
+        assert!(w.finish().is_err());
+    }
+
     #[test]
     fn counter_overflow_is_refused() {
         let mut w = StreamWriter::starting_at(&[1u8; 32], Vec::new(), u64::MAX);

src/keyfile.rs

@@ -124,49 +124,102 @@ pub fn encode_pem(body: &[u8]) -> String {
 }
 
 /// The block body if `data` is one `VAULT KEY` PEM block, optionally with
-/// text before it (as Go's `pem.Decode` allows) and only whitespace after.
+/// text before it and only whitespace after: a port of Go's `pem.Decode`
+/// followed by vault's checks on its result.
 pub fn decode_pem(data: &[u8]) -> Option<Vec<u8>> {
-    let begin = format!("-----BEGIN {PEM_TYPE}-----");
-    let end = format!("-----END {PEM_TYPE}-----");
-    let start = if data.starts_with(b"-----BEGIN ") {
-        0
-    } else {
-        find(data, b"\n-----BEGIN ")? + 1
-    };
-    let mut lines = data[start..].split_inclusive(|&c| c == b'\n');
-    let first = lines.next()?;
-    if trim_right(first) != begin.as_bytes() {
+    let (typ, body, rest) = go_pem_decode(data)?;
+    if typ != PEM_TYPE.as_bytes() || !go_trim_space(rest).is_empty() {
         return None;
     }
-    let mut b64 = Vec::new();
-    let mut after = None;
-    let mut consumed = start + first.len();
-    for line in lines.by_ref() {
-        consumed += line.len();
-        let t = trim_right(line);
-        if t == end.as_bytes() {
-            after = Some(consumed);
-            break;
-        }
-        if t.contains(&b':') {
-            // A PEM header line; Go accepts and ignores them.
-            continue;
-        }
-        b64.extend(t.iter().filter(|c| !matches!(c, b' ' | b'\t')));
-    }
-    let after = after?;
-    if !data[after..].iter().all(|c| c.is_ascii_whitespace()) {
-        return None;
-    }
-    base64::engine::general_purpose::STANDARD.decode(&b64).ok()
+    Some(body)
 }
 
-fn trim_right(l: &[u8]) -> &[u8] {
-    let mut e = l.len();
-    while e > 0 && matches!(l[e - 1], b' ' | b'\t' | b'\r' | b'\n') {
-        e -= 1;
+/// Go's `getLine`: up to the next LF (dropping one CR before it), with
+/// trailing spaces and tabs removed, and the rest after the LF.
+fn get_line(data: &[u8]) -> (&[u8], &[u8]) {
+    let (mut i, j) = match data.iter().position(|&c| c == b'\n') {
+        Some(i) => (i, i + 1),
+        None => (data.len(), data.len()),
+    };
+    if j > i && i > 0 && data[i - 1] == b'\r' {
+        i -= 1;
+    }
+    let mut line = &data[..i];
+    while let [rest @ .., b' ' | b'\t'] = line {
+        line = rest;
+    }
+    (line, &data[j..])
+}
+
+/// Go's `bytes.TrimSpace` (Unicode white space in UTF-8 text).
+fn go_trim_space(b: &[u8]) -> &[u8] {
+    match std::str::from_utf8(b) {
+        Ok(s) => s.trim_matches(char::is_whitespace).as_bytes(),
+        Err(_) => b.trim_ascii(),
+    }
+}
+
+/// Go's `encoding/pem.Decode`: the first well-formed block's type, bytes
+/// and the data after it. Malformed candidates are skipped, as in Go.
+fn go_pem_decode(data: &[u8]) -> Option<(Vec<u8>, Vec<u8>, &[u8])> {
+    const START: &[u8] = b"\n-----BEGIN ";
+    const END: &[u8] = b"\n-----END ";
+    const EOL: &[u8] = b"-----";
+    let mut rest = data;
+    loop {
+        if rest.starts_with(&START[1..]) {
+            rest = &rest[START.len() - 1..];
+        } else if let Some(i) = find(rest, START) {
+            rest = &rest[i + START.len()..];
+        } else {
+            return None;
+        }
+        let (type_line, r) = get_line(rest);
+        rest = r;
+        let Some(typ) = type_line.strip_suffix(EOL) else { continue };
+        let mut headers = 0;
+        loop {
+            if rest.is_empty() {
+                return None;
+            }
+            let (line, next) = get_line(rest);
+            if !line.contains(&b':') {
+                break;
+            }
+            headers += 1;
+            rest = next;
+        }
+        let (end_index, trailer_index) = if headers == 0 && rest.starts_with(&END[1..]) {
+            (0, END.len() - 1)
+        } else {
+            match find(rest, END) {
+                Some(i) => (i, i + END.len()),
+                None => continue,
+            }
+        };
+        let trailer = &rest[trailer_index..];
+        let tlen = typ.len() + EOL.len();
+        if trailer.len() < tlen {
+            continue;
+        }
+        let (t, rest_of_end) = trailer.split_at(tlen);
+        if !t.starts_with(typ) || !t.ends_with(EOL) || !get_line(rest_of_end).0.is_empty() {
+            continue;
+        }
+        // Go's StdEncoding skips CR and LF; removeSpacesAndTabs drops the rest.
+        let b64: Vec<u8> = rest[..end_index]
+            .iter()
+            .copied()
+            .filter(|c| !matches!(c, b' ' | b'\t' | b'\r' | b'\n'))
+            .collect();
+        let lenient = base64::engine::GeneralPurpose::new(
+            &base64::alphabet::STANDARD,
+            base64::engine::GeneralPurposeConfig::new().with_decode_allow_trailing_bits(true),
+        );
+        let Ok(bytes) = lenient.decode(&b64) else { continue };
+        let after = get_line(&rest[end_index + END.len() - 1..]).1;
+        return Some((typ.to_vec(), bytes, after));
     }
-    &l[..e]
 }
 
 fn find(h: &[u8], n: &[u8]) -> Option<usize> {
@@ -327,6 +380,27 @@ mod tests {
         assert!(decode_pem(format!("{pem}x").as_bytes()).is_none());
         assert!(decode_pem(pem.replace("VAULT KEY", "VAULT KEX").as_bytes()).is_none());
         assert!(decode_pem(pem.replace("-----END", "-----FIN").as_bytes()).is_none());
+        // Cases where an earlier, simpler parser differed from Go's pem.Decode.
+        // (In the second body line: a colon in the first makes it a header.)
+        let first = pem.find('\n').unwrap();
+        let mid = first + 1 + pem[first + 1..].find('\n').unwrap() + 30;
+        assert!(
+            decode_pem(format!("{}:{}", &pem[..mid], &pem[mid..]).as_bytes()).is_none(),
+            "colon inside the body"
+        );
+        assert!(
+            decode_pem(format!("{pem}\u{b}\u{a0}").as_bytes()).is_some(),
+            "Unicode space after the block"
+        );
+        assert!(decode_pem(pem.replacen("\n", "\r\n", 3).as_bytes()).is_some(), "CRLF lines");
+        assert!(
+            decode_pem(format!("-----BEGIN X\n{pem}").as_bytes()).is_some(),
+            "a bad BEGIN line before the block"
+        );
+        assert!(
+            decode_pem(format!("-----BEGIN VAULT KEY-----\nProc-Type: 4,x\n\n{}", &pem[26..]).as_bytes()).is_some(),
+            "headers"
+        );
         let mut short = body.clone();
         short.pop();
         assert_eq!(parse_body(&short).err(), Some(Error::NotAKeyFile));

src/platform/fs.rs

@@ -165,10 +165,33 @@ fn publish_inner(tmp: &Path, dst: &Path) -> io::Result<()> {
 /// atomic no-clobber publish wherever hard links work.
 #[cfg(not(windows))]
 fn link_publish(tmp: &Path, dst: &Path) -> io::Result<()> {
-    std::fs::hard_link(tmp, dst)?;
-    // The data is safely at dst; a failure to drop the temporary name is
-    // reported but dst stays.
-    std::fs::remove_file(tmp)
+    std::fs::hard_link(tmp, dst).map_err(no_atomic)?;
+    // The data is safely at dst; failing to drop the temporary name is only
+    // worth a warning.
+    if let Err(e) = std::fs::remove_file(tmp) {
+        eprintln!(
+            "vault: could not remove temporary file {}: {}",
+            tmp.display(),
+            crate::util::io_reason(&e)
+        );
+    }
+    Ok(())
+}
+
+/// A filesystem with neither RENAME_NOREPLACE nor hard links cannot publish
+/// without risking a replace; say so rather than fall back.
+#[cfg(not(windows))]
+fn no_atomic(e: io::Error) -> io::Error {
+    if e.kind() == io::ErrorKind::AlreadyExists {
+        return e;
+    }
+    io::Error::new(
+        e.kind(),
+        format!(
+            "this filesystem offers no atomic no-replace rename or hard link ({})",
+            crate::util::io_reason(&e)
+        ),
+    )
 }
 
 #[cfg(windows)]
@@ -325,9 +348,11 @@ impl Dir {
             match linkat(&self.fd, tmp, &self.fd, name, AtFlags::empty()) {
                 Ok(()) => {}
                 Err(rustix::io::Errno::EXIST) => return Err(exists_error(&dst)),
-                Err(e) => return Err(e.into()),
+                Err(e) => return Err(no_atomic(e.into())),
+            }
+            if let Err(e) = unlinkat(&self.fd, tmp, AtFlags::empty()) {
+                eprintln!("vault: could not remove temporary file {}: {e}", self.path.join(tmp).display());
             }
-            unlinkat(&self.fd, tmp, AtFlags::empty())?;
             Ok(())
         }
         #[cfg(not(unix))]
@@ -380,13 +405,27 @@ fn is_reparse(_: &std::fs::Metadata) -> bool {
     false
 }
 
+/// On Windows, also refuse names NTFS would treat specially: alternate
+/// data streams (`a:b`), reserved device names, trailing dots or spaces.
+fn windows_safe(name: &OsStr) -> bool {
+    if !cfg!(windows) {
+        return true;
+    }
+    let Some(n) = name.to_str() else { return false };
+    let stem = n.split('.').next().unwrap_or("").trim_end().to_ascii_uppercase();
+    let reserved = matches!(stem.as_str(), "CON" | "PRN" | "AUX" | "NUL" | "CONIN$" | "CONOUT$")
+        || ((stem.starts_with("COM") || stem.starts_with("LPT")) && stem.len() == 4 && stem.as_bytes()[3].is_ascii_digit());
+    !n.contains([':', '<', '>', '"', '|', '?', '*']) && !n.ends_with(['.', ' ']) && !reserved
+}
+
 /// A single, plain path component: no separators, not "." or "..".
 fn check_component(name: &OsStr) -> io::Result<()> {
     let ok = !name.is_empty()
         && name != "."
         && name != ".."
         && Path::new(name).components().count() == 1
-        && matches!(Path::new(name).components().next(), Some(std::path::Component::Normal(_)));
+        && matches!(Path::new(name).components().next(), Some(std::path::Component::Normal(_)))
+        && windows_safe(name);
     if ok {
         Ok(())
     } else {

src/store/tests.rs

@@ -458,6 +458,17 @@ fn duplicate_records_recover() {
 #[cfg(target_os = "linux")]
 #[test]
 fn repeated_failures_do_not_leak() {
+    // Thread counts are per process, and other tests run in parallel: run
+    // the real check alone in a child copy of this test binary.
+    if std::env::var_os("VAULT_LEAK_CHILD").is_none() {
+        let o = std::process::Command::new(std::env::current_exe().unwrap())
+            .args(["--exact", "store::tests::repeated_failures_do_not_leak", "--test-threads=1"])
+            .env("VAULT_LEAK_CHILD", "1")
+            .output()
+            .unwrap();
+        assert!(o.status.success(), "{}", String::from_utf8_lossy(&o.stdout));
+        return;
+    }
     let threads = || std::fs::read_dir("/proc/self/task").unwrap().count();
     let (d, s) = vault("leak");
     let mut cat = s.catalogue().unwrap();

tests/cli.rs

@@ -256,6 +256,15 @@ fn migrate_deletes_only_stored_originals() {
     // Never the vault or the key.
     let o = e.run(RUST, Some(REAL), &["add", "store"]);
     assert!(String::from_utf8_lossy(&o.stderr).contains("is the vault or its key"));
+    // Nor anything inside the vault: migrating its records would delete them.
+    let before = e.names(RUST, REAL);
+    let o = e.run(RUST, Some(REAL), &["migrate", "--yes", "store/records"]);
+    assert!(
+        String::from_utf8_lossy(&o.stderr).contains("is inside the vault"),
+        "{}",
+        String::from_utf8_lossy(&o.stderr)
+    );
+    assert_eq!(e.names(RUST, REAL), before);
 }
 
 #[cfg(unix)]