libsepol: add libfuzz based fuzzer for reading binary policies

Introduce a libfuzz[1] based fuzzer testing the parsing of a binary
policy.

Build the fuzzer in the oss-fuzz script.

[1]: https://llvm.org/docs/LibFuzzer.html

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>

libsepol/fuzz/binpolicy-fuzzer.c

@@ -0,0 +1,63 @@
+#include <sepol/debug.h>
+#include <sepol/kernel_to_cil.h>
+#include <sepol/kernel_to_conf.h>
+#include <sepol/policydb/policydb.h>
+
+extern int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+
+static int write_binary_policy(policydb_t *p, FILE *outfp)
+{
+	struct policy_file pf;
+
+	policy_file_init(&pf);
+	pf.type = PF_USE_STDIO;
+	pf.fp = outfp;
+	return policydb_write(p, &pf);
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+	policydb_t policydb = {};
+	sidtab_t sidtab = {};
+	struct policy_file pf;
+	FILE *devnull = NULL;
+
+	sepol_debug(0);
+
+	policy_file_init(&pf);
+	pf.type = PF_USE_MEMORY;
+	pf.data = (char *) data;
+	pf.len = size;
+
+	if (policydb_init(&policydb))
+		goto exit;
+
+	if (policydb_read(&policydb, &pf, /*verbose=*/0))
+		goto exit;
+
+	if (policydb_load_isids(&policydb, &sidtab))
+		goto exit;
+
+	if (policydb.policy_type == POLICY_KERN)
+		(void) policydb_optimize(&policydb);
+
+	devnull = fopen("/dev/null", "w");
+	if (!devnull)
+		goto exit;
+
+	(void) write_binary_policy(&policydb, devnull);
+
+	(void) sepol_kernel_policydb_to_conf(devnull, &policydb);
+
+	(void) sepol_kernel_policydb_to_cil(devnull, &policydb);
+
+exit:
+	if (devnull != NULL)
+		fclose(devnull);
+
+	policydb_destroy(&policydb);
+	sepol_sidtab_destroy(&sidtab);
+
+	/* Non-zero return values are reserved for future use. */
+	return 0;
+}

scripts/oss-fuzz.sh

@@ -32,7 +32,7 @@ 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:-$flags}
+export CFLAGS="${CFLAGS:-$flags} -I$DESTDIR/usr/include -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64"
 
 export CXX=${CXX:-clang++}
 export CXXFLAGS=${CXXFLAGS:-$flags}
@@ -49,11 +49,24 @@ make -C libsepol clean
 # shellcheck disable=SC2016
 make -C libsepol V=1 LD_SONAME_FLAGS='-soname,$(LIBSO),--version-script=$(LIBMAP)' -j"$(nproc)" install
 
+## secilc fuzzer ##
+
 # CFLAGS, CXXFLAGS and LIB_FUZZING_ENGINE have to be split to be accepted by
 # the compiler/linker so they shouldn't be quoted
 # shellcheck disable=SC2086
-$CC $CFLAGS -I"$DESTDIR/usr/include" -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -c -o secilc-fuzzer.o libsepol/fuzz/secilc-fuzzer.c
+$CC $CFLAGS -c -o secilc-fuzzer.o libsepol/fuzz/secilc-fuzzer.c
 # shellcheck disable=SC2086
 $CXX $CXXFLAGS $LIB_FUZZING_ENGINE secilc-fuzzer.o "$DESTDIR/usr/lib/libsepol.a" -o "$OUT/secilc-fuzzer"
 
 zip -r "$OUT/secilc-fuzzer_seed_corpus.zip" secilc/test
+
+## binary policy fuzzer ##
+
+# CFLAGS, CXXFLAGS and LIB_FUZZING_ENGINE have to be split to be accepted by
+# the compiler/linker so they shouldn't be quoted
+# shellcheck disable=SC2086
+$CC $CFLAGS -c -o binpolicy-fuzzer.o libsepol/fuzz/binpolicy-fuzzer.c
+# shellcheck disable=SC2086
+$CXX $CXXFLAGS $LIB_FUZZING_ENGINE binpolicy-fuzzer.o "$DESTDIR/usr/lib/libsepol.a" -o "$OUT/binpolicy-fuzzer"
+
+zip -j "$OUT/binpolicy-fuzzer_seed_corpus.zip" libsepol/fuzz/policy.bin