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Clear set-ID bits when securing the Windows VM mount sources #9605

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Clear set-ID bits when securing the Windows VM mount sources #9605

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9 changes: 6 additions & 3 deletions bin/omarchy-windows-vm
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Original file line number Diff line number Diff line change
Expand Up @@ -580,14 +580,17 @@ prepare_caller_mounts() {
# Privacy is an explicit preflight step for both already-pinned sources, not
# a side effect halfway through the two-mount transaction. Old umask-022
# installs are hardened together before either Docker-facing anchor changes.
chmod 0700 -- "/proc/$BASHPID/fd/$storage_fd" "/proc/$BASHPID/fd/$shared_fd" || {
# Symbolic, because a numeric mode leaves S_ISGID standing on a directory and
# the mode check below then rejects a source we were asked to secure.
chmod u=rwx,go=,a-s -- "/proc/$BASHPID/fd/$storage_fd" "/proc/$BASHPID/fd/$shared_fd" || {
exec {storage_fd}<&-
exec {shared_fd}<&-
return 1
}
storage_mode=$(stat -Lc '%a' "/proc/$BASHPID/fd/$storage_fd" 2>/dev/null) || storage_mode=""
shared_mode=$(stat -Lc '%a' "/proc/$BASHPID/fd/$shared_fd" 2>/dev/null) || shared_mode=""
if [[ $storage_mode != 700 || $shared_mode != 700 ]]; then
echo "omarchy-windows-vm: could not secure mount sources to mode 700 (storage=$storage_mode shared=$shared_mode)" >&2
exec {storage_fd}<&-
exec {shared_fd}<&-
return 1
Expand Down Expand Up @@ -1015,7 +1018,7 @@ prepare_user_mount_sources() {
echo "omarchy-windows-vm: storage and shared must be different directories" >&2
return 1
}
chmod 0700 -- "$storage" "$shared"
chmod u=rwx,go=,a-s -- "$storage" "$shared"
}

storage_space_path() {
Expand Down Expand Up @@ -1058,7 +1061,7 @@ write_credentials() {
local username="$1" password="$2" old_umask dir tmp
dir=$(dirname -- "$CREDENTIALS_FILE")
mkdir -p "$dir" || return 1
chmod 0700 "$dir" || return 1
chmod u=rwx,go=,a-s -- "$dir" || return 1
old_umask=$(umask)
umask 077
tmp=$(mktemp "$dir/.credentials.XXXXXX") || { umask "$old_umask"; return 1; }
Expand Down
23 changes: 23 additions & 0 deletions test/shell.d/windows-vm-compose-test.sh
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Expand Up @@ -176,6 +176,22 @@ resolve_caller
find "$CALLER_DATA_ROOT" -name 'rejected-*' -print -quit | grep -q . && fail "source was quarantined"
pass "invalid second source leaves paths and anchors untouched and leaks no FD"

# A set-ID bit on either source must not survive the privacy step. `chmod 0700`
# leaves S_ISGID standing on a directory, and the exact mode 700 the elevated
# path then demands would reject a source it had just been asked to secure.
reset_case
mkdir -p "$HOME/.windows" "$HOME/Windows"
chmod 2700 "$HOME/.windows"
chmod 6700 "$HOME/Windows"
prepare_user_mount_sources
[[ $(stat -Lc '%a' "$HOME/.windows") == 700 ]] || fail "setgid storage source was not cleared to 700"
[[ $(stat -Lc '%a' "$HOME/Windows") == 700 ]] || fail "setuid/setgid shared source was not cleared to 700"
chmod 2700 "$HOME/.windows"
write 4G 2 64G setgid pw UTC
resolve_caller
[[ $(stat -Lc '%a' "$EXPECTED_STORAGE") == 700 && $(stat -Lc '%a' "$EXPECTED_SHARED") == 700 ]] || fail "mount leaves are not private after a set-ID source"
pass "a set-ID bit on either source is cleared instead of failing the mount"

# Distinct caller-owned symlink targets are supported and remain links.
reset_case
external_storage="$TMPDIR/external-storage"
Expand Down Expand Up @@ -477,6 +493,13 @@ unset -f mv
! find "$credentials_dir" -name '.credentials.*' -print -quit | grep -q . || fail "failed credentials write left a temporary file"
pass "credentials are atomically replaced as a private regular file"

# The directory holding the plaintext password is hardened the same way, so a
# set-ID bit inherited from its parent cannot hand new credentials a group.
chmod 2755 "$credentials_dir"
write_credentials dave 'another-pw'
[[ $(stat -c '%a' "$credentials_dir") == 700 ]] || fail "credentials directory kept a set-ID bit"
pass "a set-ID bit on the credentials directory is cleared"

# Free-space accounting follows the real storage target.
reset_case
mkdir -p "$external_storage" "$HOME/Windows"
Expand Down