Control: tags -1 + patch
Hello,
I reproduced this issue against mmdebstrap 1.5.7-3.
The fallback comes from File::Temp::tempdir(..., TMPDIR => 1), which delegates
directory selection to File::Spec->tmpdir and may skip an unusable TMPDIR in
favour of another writable candidate such as /tmp.
The attached patch treats a non-empty explicit TMPDIR as the exact parent
directory by using File::Temp's DIR option at the actual temporary-root
creation call. It preserves the existing system temporary-directory behaviour
when TMPDIR is unset or empty.
The patch also adds a regression test for an unwritable explicit TMPDIR,
verifies that no /tmp/mmdebstrap.* fallback is selected, and clarifies that
this temporary-root path is used for tar, squashfs, ext2, ext4, and null output.
Verification on Ubuntu 24.04 covered unset, empty, writable, unwritable,
missing, and non-directory TMPDIR values. Perl syntax, Perl::Critic severity 4,
POD rendering, the 79-character code-line limit, and the rendered regression
test's ShellCheck and shfmt checks passed.
The complete 283-case source matrix and Debian autopkgtest were not run.
Regards,
Leo (Meng Hsi) Li
GitHub: @teamleaderleo
diff --git a/mmdebstrap b/mmdebstrap
--- a/mmdebstrap
+++ b/mmdebstrap
@@ -6868,7 +6868,11 @@
}
- # since the output is a tarball, we create the rootfs in a temporary
- # directory
+ # create the rootfs in a temporary directory before creating or
+ # discarding the requested output
- $options->{root} = tempdir('mmdebstrap.XXXXXXXXXX', TMPDIR => 1);
+ my @tempdir_options = (TMPDIR => 1);
+ if (defined $ENV{TMPDIR} && $ENV{TMPDIR} ne '') {
+ @tempdir_options = (DIR => $ENV{TMPDIR});
+ }
+ $options->{root} = tempdir('mmdebstrap.XXXXXXXXXX', @tempdir_options);
info "using $options->{root} as tempdir";
# add an flock on the temporary directory to prevent cleanup by systemd
# see section Age in tmpfiles.d(5)
@@ -8970,11 +8974,16 @@
=item C<TMPDIR>
-When creating a tarball, a temporary directory is populated with the rootfs
-before the tarball is packed. The location of that temporary directory will be
-in F</tmp> or the location pointed to by C<TMPDIR> if that environment variable
-is set. Setting C<TMPDIR> to a different directory than F</tmp> is useful if
-you have F</tmp> on a tmpfs that is too small for your rootfs.
+For the C<tar>, C<squashfs>, C<ext2>, C<ext4>, and C<null> formats,
+B<mmdebstrap> populates a temporary directory with the root filesystem before
+creating or discarding the requested output.
+
+If C<TMPDIR> is unset or empty, the directory is created in the system
+temporary location, usually F</tmp>. If C<TMPDIR> is set to a non-empty value,
+B<mmdebstrap> creates the temporary root below that directory and exits with an
+error if it cannot do so. Setting C<TMPDIR> to a different directory than
+F</tmp> is useful if F</tmp> is on a tmpfs that is too small for the root
+filesystem.
If you set C<TMPDIR> in B<unshare> mode, then the unshared user must be able to
access the directory. This means that the directory itself must be
diff --git a/coverage.txt b/coverage.txt
--- a/coverage.txt
+++ b/coverage.txt
@@ -114,6 +114,10 @@ Test: custom-tmpdir
Needs-Root: true
Modes: unshare
+Test: fail-with-unwritable-tmpdir
+Needs-Root: true
+Modes: chrootless
+
Test: xz-compressed-tarball
Test: directory-ending-in-tar
diff --git a/tests/fail-with-unwritable-tmpdir b/tests/fail-with-unwritable-tmpdir
new file mode 100755
--- /dev/null
+++ b/tests/fail-with-unwritable-tmpdir
@@ -0,0 +1,41 @@
+#!/bin/sh
+set -eu
+export LC_ALL=C.UTF-8
+
+[ "$(id -u)" -eq 0 ]
+
+if ! id "${SUDO_USER:-user}" >/dev/null 2>&1; then
+ if [ ! -e /mmdebstrap-testenv ]; then
+ echo "this test modifies the system and should only be run inside a container" >&2
+ exit 1
+ fi
+ useradd --home-dir "/home/${SUDO_USER:-user}" --create-home "${SUDO_USER:-user}"
+fi
+prefix="runuser -u ${SUDO_USER:-user} --"
+homedir=$($prefix sh -c 'cd && pwd')
+tmpdir="$homedir/mmdebstrap-unwritable-tmpdir"
+$prefix mkdir "$tmpdir"
+chmod 0555 "$tmpdir"
+trap 'chmod 0700 "$tmpdir"; rm -rf "$tmpdir"' EXIT INT TERM
+
+if $prefix touch "$tmpdir/should-fail" 2>/dev/null; then
+ echo "test setup failed: TMPDIR is writable" >&2
+ exit 1
+fi
+
+ret=0
+output="$($prefix env TMPDIR="$tmpdir" {{ CMD }} \
+ --dry-run --mode={{ MODE }} --variant=apt \
+ {{ DIST }} /dev/null {{ MIRROR }} 2>&1)" || ret=$?
+
+if [ "$ret" = 0 ]; then
+ echo "expected failure but got exit $ret" >&2
+ exit 1
+fi
+
+printf '%s\n' "$output" | grep -F "$tmpdir"
+
+if printf '%s\n' "$output" | grep -F 'I: using /tmp/mmdebstrap.'; then
+ echo "mmdebstrap silently fell back to /tmp" >&2
+ exit 1
+fi
