libsepol/cil: move the fuzz target and build script to the selinux re…

…pository

It should make it easier to reproduce bugs found by OSS-Fuzz locally
without docker. The fuzz target can be built and run with the corpus
OSS-Fuzz has accumulated so far by running the following commands:
```
./scripts/oss-fuzz.sh
wget https://storage.googleapis.com/selinux-backup.clusterfuzz-external.appspot.com/corpus/libFuzzer/selinux_secilc-fuzzer/public.zip
unzip -d CORPUS public.zip
./out/secilc-fuzzer CORPUS/
```

It was tested in google/oss-fuzz#6026
by pointing OSS-Fuzz to the branch containing the patch and
running all the tests with all the sanitizers and fuzzing engines
there: https://github.com/google/oss-fuzz/actions/runs/1024673143

Signed-off-by: Evgeny Vereshchagin <evvers@ya.ru>

libsepol/fuzz/secilc-fuzzer.c

@@ -0,0 +1,69 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <getopt.h>
+#include <sys/stat.h>
+
+#include <sepol/cil/cil.h>
+#include <sepol/policydb.h>
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+	enum cil_log_level log_level = CIL_ERR;
+	struct sepol_policy_file *pf = NULL;
+	FILE *dev_null = NULL;
+	int target = SEPOL_TARGET_SELINUX;
+	int disable_dontaudit = 0;
+	int multiple_decls = 0;
+	int disable_neverallow = 0;
+	int preserve_tunables = 0;
+	int policyvers = POLICYDB_VERSION_MAX;
+	int mls = -1;
+	int attrs_expand_generated = 0;
+	struct cil_db *db = NULL;
+	sepol_policydb_t *pdb = NULL;
+
+	cil_set_log_level(log_level);
+
+	cil_db_init(&db);
+	cil_set_disable_dontaudit(db, disable_dontaudit);
+	cil_set_multiple_decls(db, multiple_decls);
+	cil_set_disable_neverallow(db, disable_neverallow);
+	cil_set_preserve_tunables(db, preserve_tunables);
+	cil_set_mls(db, mls);
+	cil_set_target_platform(db, target);
+	cil_set_policy_version(db, policyvers);
+	cil_set_attrs_expand_generated(db, attrs_expand_generated);
+
+	if (cil_add_file(db, "fuzz", (const char *)data, size) != SEPOL_OK)
+		goto exit;
+
+	if (cil_compile(db) != SEPOL_OK)
+		goto exit;
+
+	if (cil_build_policydb(db, &pdb) != SEPOL_OK)
+		goto exit;
+
+	if (sepol_policydb_optimize(pdb) != SEPOL_OK)
+		goto exit;
+
+	dev_null = fopen("/dev/null", "w");
+	if (dev_null == NULL)
+		goto exit;
+
+	if (sepol_policy_file_create(&pf) != 0)
+		goto exit;
+
+	sepol_policy_file_set_fp(pf, dev_null);
+
+	if (sepol_policydb_write(pdb, pf) != 0)
+		goto exit;
+exit:
+	if (dev_null != NULL)
+		fclose(dev_null);
+
+	cil_db_destroy(&db);
+	sepol_policydb_free(pdb);
+	sepol_policy_file_free(pf);
+	return 0;
+}

scripts/oss-fuzz.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+set -eux
+
+export DESTDIR=$(pwd)/DESTDIR
+
+SANITIZER=${SANITIZER:-address}
+flags="-O1 -fno-omit-frame-pointer -gline-tables-only -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=$SANITIZER -fsanitize=fuzzer-no-link"
+
+export CC=${CC:-clang}
+export CFLAGS=${CFLAGS:-$flags}
+
+export CXX=${CXX:-clang++}
+export CXXFLAGS=${CXXFLAGS:-$flags}
+
+export LDFLAGS="${LDFLAGS:-} $CFLAGS"
+
+export OUT=${OUT:-$(pwd)/out}
+mkdir -p $OUT
+
+export LIB_FUZZING_ENGINE=${LIB_FUZZING_ENGINE:--fsanitize=fuzzer}
+
+find -name Makefile | xargs sed -i 's/,-z,defs//'
+make V=1 -j$(nproc) install
+
+$CC $CFLAGS -I$DESTDIR/usr/include -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -c -o secilc-fuzzer.o libsepol/fuzz/secilc-fuzzer.c
+$CXX $CXXFLAGS $LIB_FUZZING_ENGINE secilc-fuzzer.o $DESTDIR/usr/lib/libsepol.a -o $OUT/secilc-fuzzer
+zip -r $OUT/secilc-fuzzer_seed_corpus.zip secilc/test