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.

src/fuzz/fuzz-dns-packet.c

@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+/***
+  Copyright 2018 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/>.
+***/
+
+#include "fuzz.h"
+#include "resolved-dns-packet.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        int r;
+
+        if (size > DNS_PACKET_SIZE_MAX)
+                return 0;
+
+        r = dns_packet_new(&p, DNS_PROTOCOL_DNS, 0, DNS_PACKET_SIZE_MAX);
+        if (r < 0)
+                return 0;
+        p->size = 0; /* by default append starts after the header, undo that */
+        dns_packet_append_blob(p, data, size, NULL);
+        if (size < DNS_PACKET_HEADER_SIZE) {
+                /* make sure we pad the packet back up to the minimum header size */
+                assert(p->allocated >= DNS_PACKET_HEADER_SIZE);
+                memzero(DNS_PACKET_DATA(p) + size, DNS_PACKET_HEADER_SIZE - size);
+                p->size = DNS_PACKET_HEADER_SIZE;
+        }
+        dns_packet_extract(p);
+
+        return 0;
+}

src/fuzz/fuzz-dns-packet.options

@@ -0,0 +1,2 @@
+[libfuzzer]
+max_len = 65535

src/fuzz/fuzz-main.c

@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+/***
+  Copyright 2018 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/>.
+***/
+
+#include "alloc-util.h"
+#include "log.h"
+#include "fileio.h"
+#include "fuzz.h"
+
+/* This is a test driver for the systemd fuzzers that provides main function
+ * for regression testing outside of oss-fuzz (https://github.com/google/oss-fuzz)
+ *
+ * It reads files named on the command line and passes them one by one into the
+ * fuzzer that it is compiled into. */
+
+int main(int argc, char **argv) {
+        int i, r;
+        size_t size;
+        char *name;
+
+        log_set_max_level(LOG_DEBUG);
+        for (i = 1; i < argc; i++) {
+                _cleanup_free_ char *buf = NULL;
+
+                name = argv[i];
+                r = read_full_file(name, &buf, &size);
+                if (r < 0) {
+                        log_error_errno(r, "Failed to open '%s': %m", name);
+                        return EXIT_FAILURE;
+                }
+                printf("%s... ", name);
+                fflush(stdout);
+                (void)LLVMFuzzerTestOneInput((uint8_t*)buf, size);
+                printf("ok\n");
+        }
+        return EXIT_SUCCESS;
+}

src/fuzz/fuzz.h

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+/***
+  Copyright 2018 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/>.
+***/
+
+#include <stddef.h>
+#include <stdint.h>
+
+/* The entry point into the fuzzer */
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);

src/fuzz/meson.build

@@ -0,0 +1,25 @@
+# SPDX-License-Identifier: LGPL-2.1+
+# Copyright 2018 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/>.
+
+fuzzers += [
+        [['src/fuzz/fuzz-dns-packet.c',
+          dns_type_headers],
+         [libsystemd_resolve_core,
+          libshared],
+         [libgcrypt,
+          libgpg_error,
+          libm]],
+]