lib/fuzzing: fuzz_conditional_ace_blob

This parses the blob as a conditional ACE, and if possible tries
decompiling it into SDDL.

There are not many round-trip assertions we can honestly make, but we
keep the trip going as long as possible, in case it reveals anything.

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

diff --git a/lib/fuzzing/fuzz_conditional_ace_blob.c b/lib/fuzzing/fuzz_conditional_ace_blob.c
new file mode 100644 (file)
index 0000000..aed1cd3
--- /dev/null
+++ b/lib/fuzzing/fuzz_conditional_ace_blob.c
@@ -0,0 +1,144 @@
+/*
+  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) {
+               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,
+                                        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 docompilation 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;
+}

diff --git a/lib/fuzzing/wscript_build b/lib/fuzzing/wscript_build
index da972ddbae761f23314029b24251bc8b069fe75c..1e796bf3cb6b48f8b00bee7e3778d57ef1ddfd0c 100644 (file)
--- a/lib/fuzzing/wscript_build
+++ b/lib/fuzzing/wscript_build
@@ -42,6 +42,11 @@ bld.SAMBA_BINARY('fuzz_sess_crypt_blob',
                  deps='fuzzing samba-security LIBCLI_AUTH NDR_DSSETUP  afl-fuzz-main',
                  fuzzer=True)
 
+bld.SAMBA_BINARY('fuzz_conditional_ace_blob',
+                 source='fuzz_conditional_ace_blob.c',
+                 deps='fuzzing samba-security  afl-fuzz-main',
+                 fuzzer=True)
+
 bld.SAMBA_BINARY('fuzz_nmblib_parse_packet',
                  source='fuzz_nmblib_parse_packet.c',
                  deps='fuzzing libsmb afl-fuzz-main',