samba-mirror/lib/fuzzing/fuzz_conditional_ace_blob.c

/*
  Fuzz conditional ace decoding and encoding
  Copyright (C) Catalyst IT 2023

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 3 of the License, or
  (at your option) any later version.

  This program 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 General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "replace.h"
#include "libcli/security/security.h"
#include "lib/util/attr.h"
#include "librpc/gen_ndr/ndr_security.h"
#include "libcli/security/conditional_ace.h"
#include "librpc/gen_ndr/conditional_ace.h"
#include "fuzzing/fuzzing.h"


#define MAX_LENGTH (1024 * 1024 - 1)


int LLVMFuzzerInitialize(int *argc, char ***argv)
{
	return 0;
}


int LLVMFuzzerTestOneInput(const uint8_t *input, size_t len)
{
	TALLOC_CTX *mem_ctx = NULL;
	bool ok;
	struct ace_condition_script *s1 = NULL;
	struct ace_condition_script *s2 = NULL;
	const char *message = NULL;
	size_t message_offset;
	const char *sddl = NULL;
	DATA_BLOB e1, e2;
	size_t length;

	if (len > MAX_LENGTH) {
		return 0;
	}

	/*
	 * In this one we are treating the input data as an ACE blob,
	 * and decoding it into the structure and thence SDDL.
	 *
	 * This doesn't run the conditional ACE, for which we would
	 * need a security token.
	 */

	e1.data = input;
	e1.length = len;

	mem_ctx = talloc_new(NULL);

	s1 = parse_conditional_ace(mem_ctx, e1);
	if (s1 == NULL) {
		/* no worries, it was nonsense */
		TALLOC_FREE(mem_ctx);
		return 0;
	}

	/* back to blob form */
	ok = conditional_ace_encode_binary(mem_ctx, s1, &e2);
	if (! ok) {
		if (e1.length == CONDITIONAL_ACE_MAX_LENGTH) {
			/*
			 * This is an edge case where the encoder and
			 * decoder treat the boundary slightly
			 * differently, and the encoder refuses to
			 * encode to the maximum length. This is not
			 * an issue in the real world.
			 */
			TALLOC_FREE(mem_ctx);
			return 0;
		}
		abort();
	}

	if (data_blob_cmp(&e1, &e2) != 0) {
		abort();
	}

	sddl = sddl_from_conditional_ace(mem_ctx, s1);
	if (sddl == NULL) {
		/*
		 * we can't call this a failure, because the blob
		 * could easily have nonsensical programs that the
		 * SDDL decompiler is unwilling to countenance. For
		 * example, it could have an operator that requires
		 * arguments as the first token, when of course the
		 * arguments need to come first.
		 */
		TALLOC_FREE(mem_ctx);
		return 0;
	}

	s2 = ace_conditions_compile_sddl(mem_ctx,
					 ACE_CONDITION_FLAG_ALLOW_DEVICE,
					 sddl,
					 &message,
					 &message_offset,
					 &length);
	if (s2 == NULL) {
		/*
		 * We also don't complain when the SDDL decompiler
		 * produces an uncompilable program, because the
		 * decompiler is meant to be a display tool, not a
		 * verifier in itself.
		 */
		TALLOC_FREE(mem_ctx);
		return 0;
	}

	ok = conditional_ace_encode_binary(mem_ctx, s2, &e2);
	if (! ok) {
		abort();
	}

	/*
	 * It would be nice here to go:
	 *
	 * if (data_blob_cmp(&e1, &e2) != 0) {
	 *       abort();
	 * }
	 *
	 * but that isn't really fair. The decompilation into SDDL
	 * does not make thorough sanity checks because that is not
	 * its job -- it is just trying to depict what is there -- and
	 * there are many ambiguous decompilations.
	 *
	 * For example, a blob with a single literal integer token,
	 * say 42, can only really be shown in the SDDL syntax as
	 * "(42)", but when the compiler reads that it knows that a
	 * literal number is invalid except in a RHS argument, so it
	 * assumes "42" is a local attribute name.
	 *
	 * Even if the decompiler was a perfect verifier, a round trip
	 * through SDDL could not be guaranteed because, for example,
	 * an 8 bit integer can only be displayed in SDDL in the form
	 * that compiles to a 64 bit integer.
	 */

	TALLOC_FREE(mem_ctx);
	return 0;
}