lib/fuzzing: add fuzzer for arbitrary token/sd access checks

The token and descriptor are stored in NDR format; for this purpose we
add a new IDL struct containing this pair (along with a desired access
mask).

An upcoming commit will show how to collect seeds for this fuzzer.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

lib/fuzzing/fuzz_security_token_vs_descriptor.c

@@ -0,0 +1,60 @@
+/*
+  Fuzz a security token and descriptor through an access check
+  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 "librpc/gen_ndr/ndr_security.h"
+#include "libcli/security/security.h"
+#include "fuzzing/fuzzing.h"
+
+
+int LLVMFuzzerInitialize(int *argc, char ***argv)
+{
+	return 0;
+}
+
+
+int LLVMFuzzerTestOneInput(uint8_t *input, size_t len)
+{
+	TALLOC_CTX *mem_ctx = NULL;
+	struct security_token_descriptor_fuzzing_pair p = {0};
+	enum ndr_err_code ndr_err;
+	uint32_t access_granted;
+
+	DATA_BLOB blob = {
+		.data = input,
+		.length = len
+	};
+
+	mem_ctx = talloc_new(NULL);
+
+	ndr_err = ndr_pull_struct_blob(
+		&blob, mem_ctx, &p,
+		(ndr_pull_flags_fn_t)ndr_pull_security_token_descriptor_fuzzing_pair);
+
+	if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
+		goto end;
+	}
+	se_access_check(&p.sd,
+			&p.token,
+			p.access_desired,
+			&access_granted);
+
+end:
+	talloc_free(mem_ctx);
+	return 0;
+}

lib/fuzzing/wscript_build

@@ -132,6 +132,12 @@ bld.SAMBA_BINARY('fuzz_stable_sort_r',
                  deps='fuzzing stable_sort afl-fuzz-main',
                  fuzzer=True)
 
+bld.SAMBA_BINARY('fuzz_security_token_vs_descriptor',
+                 source='fuzz_security_token_vs_descriptor.c',
+                 deps='fuzzing samba-security afl-fuzz-main',
+                 fuzzer=True)
+
+
 # The fuzz_type and fuzz_function parameters make the built
 # fuzzer take the same input as ndrdump and so the same that
 # could be sent to the client or server as the stub data.

librpc/idl/security.idl

@@ -678,6 +678,12 @@ interface security
 		lsa_SystemAccessModeFlags rights_mask;
 	} security_token;
 
+        typedef [public] struct {
+                security_token token;
+                security_descriptor sd;
+                uint32 access_desired;
+        } security_token_descriptor_fuzzing_pair;
+
 	/* This is not yet sent over the network, but is simply defined in IDL */
 	typedef [public] struct {
 		uid_t uid;