fuzz: add initial fuzzing infrastructure

The fuzzers will be used by oss-fuzz to automatically and
continuously fuzz systemd.

This commit includes the build tooling necessary to build fuzz
targets, and a fuzzer for the DNS packet parser.

scripts/oss-fuzz.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+# SPDX-License-Identifier: LGPL-2.1+
+#
+# Copyright 2017 Jonathan Rudenberg
+#
+# systemd is free software; you can redistribute it and/or modify it
+# under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation; either version 2.1 of the License, or
+# (at your option) any later version.
+#
+# systemd is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with systemd; If not, see <http://www.gnu.org/licenses/>.
+
+set -ex
+
+export LC_CTYPE=C.UTF-8
+
+meson $WORK -Doss-fuzz=true -Db_lundef=false -Dseccomp=false -Dlz4=false -Dlibiptc=false -Dlibidn=false
+ninja -C $WORK fuzzers
+
+# get DNS packet corpus
+df=$WORK/dns-fuzzing
+rm -rf $df
+git clone --depth 1 https://github.com/CZ-NIC/dns-fuzzing $df
+zip -jqr $OUT/fuzz-dns-packet_seed_corpus.zip $df/packet
+
+mkdir -p $OUT/src/shared
+mv $WORK/src/shared/libsystemd-shared-*.so $OUT/src/shared
+
+find $WORK -maxdepth 1 -type f -executable -name "fuzz-*" -exec mv {} $OUT \;
+mv $WORK/*.so src/fuzz/*.options $OUT