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fix(mv): don't destroy the destination when a cross-device move fails #13334

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fix(mv): don't destroy the destination when a cross-device move fails #13334

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162 changes: 119 additions & 43 deletions src/uu/mv/src/mv.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -793,13 +793,18 @@ fn rename(
Ok(())
}

/// Check if a file type must be recreated with [`copy_special_file`] rather
/// than copied by content: fifos, sockets, and device nodes.
#[cfg(unix)]
fn is_fifo(filetype: fs::FileType) -> bool {
fn is_special_file(filetype: fs::FileType) -> bool {
filetype.is_fifo()
|| filetype.is_socket()
|| filetype.is_block_device()
|| filetype.is_char_device()
}

#[cfg(not(unix))]
fn is_fifo(_filetype: fs::FileType) -> bool {
fn is_special_file(_filetype: fs::FileType) -> bool {
false
}

Expand Down Expand Up @@ -859,8 +864,8 @@ fn rename_with_fallback(
{
rename_dir_fallback(from, to, display_manager, verbose)
}
} else if is_fifo(file_type) {
rename_fifo_fallback(from, to)
} else if is_special_file(file_type) {
rename_special_fallback(from, to, &metadata)
} else {
#[cfg(unix)]
{
Expand All @@ -878,23 +883,80 @@ fn rename_with_fallback(
})
}

/// Replace the destination with a new pipe with the same name as the source.
/// Recreate the source special file (fifo, socket, or device node) at `to`,
/// preserving its ownership and permissions.
#[cfg(unix)]
fn rename_fifo_fallback(from: &Path, to: &Path) -> io::Result<()> {
if to.try_exists()? {
fs::remove_file(to)?;
fn copy_special_file(from: &Path, metadata: &fs::Metadata, to: &Path) -> io::Result<()> {
use nix::sys::stat::{Mode, SFlag, mknod};
use std::fs::Permissions;
use std::os::unix::fs::MetadataExt;

let file_type = metadata.file_type();
let mode = Mode::from_bits_truncate(metadata.mode() as _);
if file_type.is_fifo() {
// rustix::fs::mkfifoat is linux only
nix::unistd::mkfifo(to, mode)?;
} else {
let kind = if file_type.is_socket() {
SFlag::S_IFSOCK
} else if file_type.is_block_device() {
SFlag::S_IFBLK
} else {
SFlag::S_IFCHR
};
mknod(to, kind, mode, metadata.rdev() as _)?;
}
// rustix::fs::mkfifoat is linux only
nix::unistd::mkfifo(to, nix::sys::stat::Mode::from_bits_truncate(0o666))?;
fs::remove_file(from)
// chown before chmod: chown(2) clears setuid/setgid for non-root, and the
// explicit chmod undoes the umask applied during creation.
let _ = preserve_ownership(from, to);
let _ = fs::set_permissions(to, Permissions::from_mode(metadata.mode() & 0o7777));
Ok(())
}

/// Replace the destination with a new special file (fifo, socket, or device
/// node) with the same name as the source. The node is created under a
/// temporary name and then renamed over the destination, so that failing to
/// create it cannot destroy an existing destination.
#[cfg(unix)]
fn rename_special_fallback(from: &Path, to: &Path, metadata: &fs::Metadata) -> io::Result<()> {
use std::ffi::OsStr;
use std::os::unix::ffi::OsStrExt;

let parent = to
.parent()
.filter(|p| !p.as_os_str().is_empty())
.unwrap_or_else(|| Path::new("."));

let mut urandom = fs::File::open("/dev/urandom")?;

for _ in 0..32 {
let tmp_bytes = random_temp_name(&mut urandom)?;
let tmp = parent.join(OsStr::from_bytes(&tmp_bytes));

match copy_special_file(from, metadata, &tmp) {
Ok(()) => {
if let Err(e) = fs::rename(&tmp, to) {
let _ = fs::remove_file(&tmp);
return Err(e);
}
return fs::remove_file(from);
}
Err(e) if e.kind() == io::ErrorKind::AlreadyExists => {}
Err(e) => return Err(e),
}
}
Err(io::Error::new(
io::ErrorKind::AlreadyExists,
"could not allocate a unique temp name in destination directory",
))
}

#[cfg(not(unix))]
#[expect(
clippy::unnecessary_wraps,
reason = "fn sig must match on all platforms"
)]
fn rename_fifo_fallback(_from: &Path, _to: &Path) -> io::Result<()> {
fn rename_special_fallback(_from: &Path, _to: &Path, _metadata: &fs::Metadata) -> io::Result<()> {
Ok(())
}

Expand Down Expand Up @@ -927,6 +989,26 @@ fn rename_symlink_fallback(from: &Path, to: &Path) -> io::Result<()> {
fs::remove_file(from)
}

/// Generate a temp file name for atomically replacing a destination entry.
///
/// GNU's template is `CuXXXXXX`: a 2-char prefix plus 6 random chars
/// drawn from a 62-char alphabet. Modulo bias on a 256→62 mapping is
/// ~3% per slot — irrelevant for an 8-char unguessability budget. The
/// name is drawn from `/dev/urandom` so it is unguessable to other
/// users in the destination directory.
#[cfg(unix)]
fn random_temp_name(urandom: &mut impl io::Read) -> io::Result<[u8; 8]> {
const ALPHABET: &[u8; 62] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

let mut tmp_bytes = *b"Cu------";
let mut raw = [0u8; 6];
urandom.read_exact(&mut raw)?;
for (slot, byte) in tmp_bytes[2..].iter_mut().zip(raw) {
*slot = ALPHABET[(byte as usize) % ALPHABET.len()];
}
Ok(tmp_bytes)
}

/// Create a symlink at `to`, atomically replacing any existing entry via
/// a temp-name + `renameat(2)` so observers never see `to` missing.
///
Expand All @@ -937,16 +1019,10 @@ fn rename_symlink_fallback(from: &Path, to: &Path) -> io::Result<()> {
/// directory.
#[cfg(all(unix, not(target_os = "redox")))]
fn create_symlink_replace(target: &Path, to: &Path) -> io::Result<()> {
use io::Read;
use rustix::fs::{AtFlags, CWD, Mode, OFlags, openat, renameat, symlinkat, unlinkat};
use std::ffi::OsStr;
use std::os::unix::ffi::OsStrExt;

// GNU's template is `CuXXXXXX`: a 2-char prefix plus 6 random chars
// drawn from a 62-char alphabet. Modulo bias on a 256→62 mapping is
// ~3% per slot — irrelevant for an 8-char unguessability budget.
const ALPHABET: &[u8; 62] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

let parent = to
.parent()
.filter(|p| !p.as_os_str().is_empty())
Expand All @@ -965,12 +1041,7 @@ fn create_symlink_replace(target: &Path, to: &Path) -> io::Result<()> {
let mut urandom = fs::File::open("/dev/urandom")?;

for _ in 0..32 {
let mut tmp_bytes = *b"Cu------";
let mut raw = [0u8; 6];
urandom.read_exact(&mut raw)?;
for (slot, byte) in tmp_bytes[2..].iter_mut().zip(raw) {
*slot = ALPHABET[(byte as usize) % ALPHABET.len()];
}
let tmp_bytes = random_temp_name(&mut urandom)?;
let tmp = OsStr::from_bytes(&tmp_bytes);

match symlinkat(target, &dir_fd, tmp) {
Expand Down Expand Up @@ -1239,21 +1310,22 @@ fn copy_file_with_hardlinks_helper(
// Copy a symlink file (no-follow).
// rename_symlink_fallback already preserves ownership and removes the source.
rename_symlink_fallback(from, to)?;
} else if is_fifo(from.symlink_metadata()?.file_type()) {
// rustix::fs::mkfifoat is linux only
nix::unistd::mkfifo(to, nix::sys::stat::Mode::from_bits_truncate(0o666))?;
// Preserve ownership (uid/gid) from the source
let _ = preserve_ownership(from, to);
} else {
// Copy a regular file.
fs::copy(from, to)?;
// Copy xattrs, ignoring ENOTSUP errors (filesystem doesn't support xattrs)
#[cfg(all(unix, not(any(target_os = "macos", target_os = "redox"))))]
{
let _ = fsxattr::copy_xattrs_ignore_unsupported(from, to);
let metadata = from.symlink_metadata()?;
if is_special_file(metadata.file_type()) {
// Recreate a fifo, socket, or device node.
copy_special_file(from, &metadata, to)?;
} else {
// Copy a regular file.
fs::copy(from, to)?;
// Copy xattrs, ignoring ENOTSUP errors (filesystem doesn't support xattrs)
#[cfg(all(unix, not(any(target_os = "macos", target_os = "redox"))))]
{
let _ = fsxattr::copy_xattrs_ignore_unsupported(from, to);
}
// Preserve ownership (uid/gid) from the source
let _ = preserve_ownership(from, to);
}
// Preserve ownership (uid/gid) from the source
let _ = preserve_ownership(from, to);
}

Ok(())
Expand All @@ -1265,6 +1337,12 @@ fn rename_file_fallback(
#[cfg(unix)] hardlink_tracker: Option<&mut HardlinkTracker>,
#[cfg(unix)] hardlink_scanner: Option<&HardlinkGroupScanner>,
) -> io::Result<()> {
// Open the source before touching the destination: a source that cannot
// be opened for reading must not cost us an existing destination.
#[cfg(unix)]
let src_file = uucore::safe_copy::open_source(from, /* nofollow */ true)
.map_err(|err| io::Error::new(err.kind(), translate!("mv-error-permission-denied")))?;

// Remove existing target file if it exists
if to.is_symlink() {
fs::remove_file(to).map_err(|err| {
Expand Down Expand Up @@ -1293,16 +1371,14 @@ fn rename_file_fallback(
}
}

// Open src/dst with O_NOFOLLOW and keep the fds alive across copy,
// chown, xattr, and chmod so a concurrent path-swap can't redirect any
// step to a different inode.
// Src/dst are open with O_NOFOLLOW and the fds are kept alive across
// copy, chown, xattr, and chmod so a concurrent path-swap can't redirect
// any step to a different inode.
#[cfg(unix)]
{
use std::fs::Permissions;
use std::os::unix::fs::{MetadataExt, PermissionsExt};
use uucore::safe_copy::{create_dest_restrictive, open_source};
let src_file = open_source(from, /* nofollow */ true)
.map_err(|err| io::Error::new(err.kind(), translate!("mv-error-permission-denied")))?;
use uucore::safe_copy::create_dest_restrictive;
let src_mode = src_file
.metadata()
.map_err(|err| io::Error::new(err.kind(), translate!("mv-error-permission-denied")))?
Expand Down
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