1 files changed, 85 insertions, 0 deletions
diff --git a/hooks/merged-usr/extract00.sh b/hooks/merged-usr/extract00.sh
new file mode 100755
index 0000000..7334191
--- /dev/null
+++ b/hooks/merged-usr/extract00.sh
@@ -0,0 +1,85 @@
+#!/bin/sh
+
+set -eu
+
+if [ "${MMDEBSTRAP_VERBOSITY:-1}" -ge 3 ]; then
+	set -x
+fi
+
+TARGET="$1"
+
+# can_usrmerge_symlink() and can_usrmerge_symlink() are
+# Copyright 2023 Helmut Grohne <helmut@subdivi.de>
+# and part of the debootstrap source in /usr/share/debootstrap/functions
+# https://salsa.debian.org/installer-team/debootstrap/-/merge_requests/96
+# https://bugs.debian.org/104989
+can_usrmerge_symlink() {
+	# Absolute symlinks can be relocated without problems.
+	test "${2#/}" = "$2" || return 0
+	while :; do
+		if test "${2#/}" != "$2"; then
+			# Handle double-slashes.
+			set -- "$1" "${2#/}"
+		elif test "${2#./}" != "$2"; then
+			# Handle ./ inside a link target.
+			set -- "$1" "${2#./}"
+		elif test "$2" = ..; then
+			# A parent directory symlink is ok if it does not
+			# cross the top level directory.
+			test "${1%/*/*}" != "$1" -a -n "${1%/*/*}"
+			return $?
+		elif test "${2#../}" != "$2"; then
+			# Symbolic link crossing / cannot be moved safely.
+			# This is prohibited by Debian Policy 10.5.
+			test "${1%/*/*}" = "$1" -o -z "${1%/*/*}" && return 1
+			set -- "${1%/*}" "${2#../}"
+		else
+			# Consider the symlink ok if its target does not
+			# contain a parent directory. When we fail here,
+			# the link target is non-minimal and doesn't happen
+			# in the archive.
+			test "${2#*/../}" = "$2"
+			return $?
+		fi
+	done
+}
+
+merge_usr_entry() {
+	# shellcheck disable=SC3043
+	local entry canon
+	canon="$TARGET/usr/${1#"$TARGET/"}"
+	test -h "$canon" &&
+		error 1 USRMERGEFAIL "cannot move %s as its destination exists as a symlink" "${1#"$TARGET"}"
+	if ! test -e "$canon"; then
+		mv "$1" "$canon"
+		return 0
+	fi
+	test -d "$1" ||
+		error 1 USRMERGEFAIL "cannot move non-directory %s as its destination exists" "${1#"$TARGET"}"
+	test -d "$canon" ||
+		error 1 USRMERGEFAIL "cannot move directory %s as its destination is not a directory" "${1#"$TARGET"}"
+	for entry in "$1/"* "$1/."*; do
+		# Some shells return . and .. on dot globs.
+		test "${entry%/.}" != "${entry%/..}" && continue
+		if test -h "$entry" && ! can_usrmerge_symlink "${entry#"$TARGET"}" "$(readlink "$entry")"; then
+			error 1 USRMERGEFAIL "cannot move relative symlink crossing top-level directory" "${entry#"$TARGET"}"
+		fi
+		# Ignore glob match failures
+		if test "${entry%'/*'}" != "${entry%'/.*'}" && ! test -e "$entry"; then
+			continue
+		fi
+		merge_usr_entry "$entry"
+	done
+	rmdir "$1"
+}
+
+# This is list includes all possible multilib directories. It must be
+# updated when new multilib directories are being added. Hopefully,
+# all new architectures use multiarch instead, so we never get to
+# update this.
+for dir in bin lib lib32 lib64 libo32 libx32 sbin; do
+	test -h "$TARGET/$dir" && continue
+	test -e "$TARGET/$dir" || continue
+	merge_usr_entry "$TARGET/$dir"
+	ln -s "usr/$dir" "$TARGET/$dir"
+done