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/*
Fuzz access check using SDDL strings and a known token
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 "libcli/security/conditional_ace.h"
#include "libcli/security/claims-conversions.h"
#include "lib/util/attr.h"
#include "librpc/gen_ndr/ndr_security.h"
#include "librpc/gen_ndr/ndr_conditional_ace.h"
#include "lib/util/bytearray.h"
#include "fuzzing/fuzzing.h"
static struct security_token token = {0};
static struct dom_sid dom_sid = {0};
/*
* For this one we initialise a security token to have a few claims
* and SIDs. The fuzz strings contain SDDL that will be tested against
* this token in se_access_check() or sec_access_check_ds() --
* supposing they compile.
*/
int LLVMFuzzerInitialize(int *argc, char ***argv)
{
size_t i;
TALLOC_CTX *mem_ctx = talloc_new(NULL);
struct dom_sid *sid = NULL;
struct claim_def {
const char *type;
const char *name;
const char *claim_sddl;
} claims[] = {
{
"user",
"shoe size",
"44"
},
{
"user",
"©",
"{\"unknown\", \"\", \" ←ā\"}"
},
{
"device",
"©",
"{\"unknown\", \" \", \" ←ā\"}"
},
{
"device",
"least favourite groups",
"{SID(S-1-1-0),SID(S-1-5-3),SID(S-1-57777-333-33-33-2)}"
},
{
"local",
"birds",
"{\"tern\"}"
},
};
const char * device_sids[] = {
"S-1-1-0",
"S-1-333-66",
"S-1-2-3-4-5-6-7-8-9",
};
const char * user_sids[] = {
"S-1-333-66",
"S-1-16-8448",
"S-1-9-8-7",
};
for (i = 0; i < ARRAY_SIZE(user_sids); i++) {
sid = sddl_decode_sid(mem_ctx, &user_sids[i], NULL);
if (sid == NULL) {
abort();
}
add_sid_to_array(mem_ctx, sid,
&token.sids,
&token.num_sids);
}
for (i = 0; i < ARRAY_SIZE(device_sids); i++) {
sid = sddl_decode_sid(mem_ctx, &device_sids[i], NULL);
if (sid == NULL) {
abort();
}
add_sid_to_array(mem_ctx, sid,
&token.device_sids,
&token.num_device_sids);
}
for (i = 0; i < ARRAY_SIZE(claims); i++) {
struct CLAIM_SECURITY_ATTRIBUTE_RELATIVE_V1 *claim = NULL;
struct claim_def c = claims[i];
claim = parse_sddl_literal_as_claim(mem_ctx,
c.name,
c.claim_sddl);
if (claim == NULL) {
abort();
}
add_claim_to_token(mem_ctx, &token, claim, c.type);
}
/* we also need a global domain SID */
string_to_sid(&dom_sid, device_sids[2]);
return 0;
}
int LLVMFuzzerTestOneInput(const uint8_t *input, size_t len)
{
TALLOC_CTX *mem_ctx = NULL;
struct security_descriptor *sd = NULL;
uint32_t access_desired;
uint32_t access_granted;
const char *sddl;
ssize_t i;
if (len < 5) {
return 0;
}
access_desired = PULL_LE_U32(input + len - 4, 0);
/*
* check there is a '\0'.
*
* Note this allows double-dealing for the last 4 bytes: they are used
* as the access_desired mask (see just above) but also *could* be
* part of the sddl string. But this doesn't matter, for three
* reasons:
*
* 1. the desired access mask doesn't usually matter much.
*
* 2. the final '\0' is rarely the operative one. Usually the
* effective string ends a long time before the end of the input, and
* the tail is just junk that comes along for the ride.
*
* 3. Even if there is a case where the end of the SDDL is part of the
* mask, the evolution strategy is very likely to try a different mask,
* because it likes to add junk on the end.
*
* But still, you ask, WHY? So that the seeds from here can be shared
* back and forth with the fuzz_sddl_parse seeds, which have the same
* form of a null-terminated-string-with-trailing-junk. If we started
* the loop at `len - 5` instead of `len - 1`, there might be
* interesting seeds that are valid there that would fail here. That's
* all.
*/
for (i = len - 1; i >= 0; i--) {
if (input[i] == 0) {
break;
}
}
if (i < 0) {
return 0;
}
sddl = (const char *)input;
mem_ctx = talloc_new(NULL);
sd = sddl_decode(mem_ctx, sddl, &dom_sid);
if (sd == NULL) {
goto end;
}
#ifdef FUZZ_SEC_ACCESS_CHECK_DS
/*
* The sec_access_check_ds() function has two arguments not found in
* se_access_check, and also not found in our fuzzing examples.
*
* One is a struct object_tree, which is used for object ACE types.
* The other is a SID, which is used as a default if an ACE lacks a
* SID.
*/
sec_access_check_ds(sd,
&token,
access_desired,
&access_granted,
NULL,
NULL);
#else
se_access_check(sd, &token, access_desired, &access_granted);
#endif
end:
talloc_free(mem_ctx);
return 0;
}
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