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/* Copyright (C) 2021 Yubico AB - See COPYING */
#include <assert.h>
#include <err.h>
#include <errno.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include "fuzz/fuzz.h"
#include "fuzz/wiredata.h"
#include "fuzz/authfile.h"
#define MUTATE_SEED 0x01
#define MUTATE_PARAM 0x02
#define MUTATE_WIREDATA 0x04
#define MUTATE_ALL (MUTATE_SEED | MUTATE_PARAM | MUTATE_WIREDATA)
size_t LLVMFuzzerMutate(uint8_t *, size_t, size_t);
int LLVMFuzzerInitialize(int *, char ***);
int LLVMFuzzerTestOneInput(const uint8_t *, size_t);
size_t LLVMFuzzerCustomMutator(uint8_t *, size_t, size_t, unsigned int);
struct param {
uint32_t seed;
char user[MAXSTR];
char conf[MAXSTR];
char conv[MAXSTR];
struct blob authfile;
struct blob wiredata;
};
struct conv_appdata {
char *str;
char *save;
};
/* fuzzer configuration */
static unsigned int flags = MUTATE_ALL;
/* it is far easier for the fuzzer to guess the native format */
static const char dummy_authfile[] = AUTHFILE_SSH;
/* module configuration split by fuzzer on semicolon */
static const char *dummy_conf = "sshformat;pinverification=0;manual;";
/* conversation dummy for manual authentication */
static const char *dummy_conv =
"94/ZgCC5htEl9SRmTRfUffKCzU/2ScRJYNFSlC5U+ik=\n"
"ssh:\n"
"WCXjBhDooWIRWWD+HsIj5lKcn0tugCANy15cMhyK8eKxvwEAAAAP\n"
"MEQCIDBrIO3J/B9Y7LJca3A7t0m76WcxoATJe0NG/"
"ZsjOMq2AiAdBGrjMalfVtzEe0rjWfnRrGhMFyRyaRuPfCHVYdIWdg==\n";
/* wiredata collected from an authenticator during authentication */
static unsigned char dummy_wiredata[] = {
WIREDATA_CTAP_INIT,
WIREDATA_CTAP_CBOR_INFO,
WIREDATA_CTAP_CBOR_ASSERT_DISCOVER,
WIREDATA_CTAP_CBOR_ASSERT_AUTHENTICATE,
};
static size_t pack(uint8_t *data, size_t len, const struct param *p) {
size_t ilen = len;
if (pack_u32(&data, &len, p->seed) != 1 ||
pack_string(&data, &len, p->user) != 1 ||
pack_string(&data, &len, p->conf) != 1 ||
pack_string(&data, &len, p->conv) != 1 ||
pack_blob(&data, &len, &p->authfile) != 1 ||
pack_blob(&data, &len, &p->wiredata) != 1) {
return 0;
}
return ilen - len;
}
static int set_blob(struct blob *blob, const void *data, size_t len) {
if (len > MAXBLOB)
return 0;
memcpy(blob->body, data, len);
blob->len = len;
return 1;
}
static int set_string(char *dst, const char *src, size_t size) {
int n;
/* FIXME: use strlcpy */
n = snprintf(dst, size, "%s", src);
if (n < 0 || (size_t) n >= size)
return 0;
return 1;
}
static size_t pack_dummy(uint8_t *data, size_t len) {
struct param dummy;
size_t r;
memset(&dummy, 0, sizeof(dummy));
if (!set_string(dummy.user, "user", MAXSTR) ||
!set_string(dummy.conf, dummy_conf, MAXSTR) ||
!set_string(dummy.conv, dummy_conv, MAXSTR) ||
!set_blob(&dummy.authfile, dummy_authfile, sizeof(dummy_authfile)) ||
!set_blob(&dummy.wiredata, dummy_wiredata, sizeof(dummy_wiredata))) {
assert(0); /* dummy couldn't be prepared */
return 0;
}
r = pack(data, len, &dummy);
assert(r != 0); /* dummy couldn't be packed */
return r;
}
static struct param *unpack(const uint8_t *data, size_t len) {
struct param *p = NULL;
if ((p = calloc(1, sizeof(*p))) == NULL ||
unpack_u32(&data, &len, &p->seed) != 1 ||
unpack_string(&data, &len, p->user) != 1 ||
unpack_string(&data, &len, p->conf) != 1 ||
unpack_string(&data, &len, p->conv) != 1 ||
unpack_blob(&data, &len, &p->authfile) != 1 ||
unpack_blob(&data, &len, &p->wiredata) != 1) {
free(p);
return NULL;
}
return p;
}
static void mutate_blob(struct blob *blob) {
blob->len =
LLVMFuzzerMutate((uint8_t *) blob->body, blob->len, sizeof(blob->body));
}
static void mutate_string(char *s, size_t maxlen) {
size_t len;
len = LLVMFuzzerMutate((uint8_t *) s, strlen(s), maxlen);
s[len - 1] = '\0';
}
static void mutate(struct param *p, uint32_t seed) {
if (flags & MUTATE_SEED)
p->seed = seed;
if (flags & MUTATE_PARAM) {
mutate_string(p->user, MAXSTR);
mutate_string(p->conf, MAXSTR);
mutate_string(p->conv, MAXSTR);
mutate_blob(&p->authfile);
}
if (flags & MUTATE_WIREDATA)
mutate_blob(&p->wiredata);
}
static void consume(const void *body, size_t len) {
const volatile uint8_t *ptr = body;
volatile uint8_t x = 0;
while (len--)
x ^= *ptr++;
}
static int conv_cb(int num_msg, const struct pam_message **msg,
struct pam_response **resp_p, void *appdata_ptr) {
struct conv_appdata *conv = appdata_ptr;
struct pam_response *resp = NULL;
const char *str = NULL;
assert(num_msg == 1);
assert(resp_p != NULL);
consume(msg[0]->msg, strlen(msg[0]->msg));
if ((*resp_p = resp = calloc(1, sizeof(*resp))) == NULL)
return PAM_CONV_ERR;
if (msg[0]->msg_style == PAM_PROMPT_ECHO_OFF ||
msg[0]->msg_style == PAM_PROMPT_ECHO_ON) {
str = strtok_r(conv->save ? NULL : conv->str, "\n", &conv->save);
if (str != NULL && (resp->resp = strdup(str)) == NULL) {
free(resp);
return PAM_CONV_ERR;
}
}
return PAM_SUCCESS;
}
static void prepare_argv(char *s, const char **argv, int *argc) {
const char *delim = ";";
char *token, *save;
int size = *argc;
*argc = 0;
token = strtok_r(s, delim, &save);
while (token != NULL && *argc < size) {
argv[(*argc)++] = token;
token = strtok_r(NULL, delim, &save);
}
}
static void prepare_conv(struct pam_conv *conv, struct conv_appdata *data,
char *str) {
data->str = str;
conv->conv = conv_cb;
conv->appdata_ptr = data;
}
static int prepare_authfile(const unsigned char *data, size_t len) {
int fd;
ssize_t r;
if ((fd = memfd_create("u2f_keys", MFD_CLOEXEC)) == -1)
return -1;
if ((r = write(fd, data, len)) == -1 || (size_t) r != len ||
lseek(fd, 0, SEEK_SET) == -1) {
close(fd);
return -1;
}
return fd;
}
int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
struct param *param = NULL;
struct pam_conv conv;
struct conv_appdata conv_data;
const char *argv[32];
int argc = 32;
int fd = -1;
memset(&argv, 0, sizeof(*argv));
memset(&conv, 0, sizeof(conv));
memset(&conv_data, 0, sizeof(conv_data));
if ((param = unpack(data, size)) == NULL)
goto err;
/* init libfido2's fuzzing prng */
prng_init(param->seed);
/* configure wrappers */
prepare_conv(&conv, &conv_data, param->conv);
set_conv(&conv);
set_user(param->user);
set_wiredata(param->wiredata.body, param->wiredata.len);
if ((fd = prepare_authfile(param->authfile.body, param->authfile.len)) == -1)
goto err;
set_authfile(fd);
prepare_argv(param->conf, &argv[0], &argc);
pam_sm_authenticate((void *) FUZZ_PAM_HANDLE, 0, argc, argv);
err:
if (fd != -1)
close(fd);
free(param);
return 0;
}
size_t LLVMFuzzerCustomMutator(uint8_t *data, size_t size, size_t maxsize,
unsigned int seed) {
size_t blob_len;
struct param *p = NULL;
if ((p = unpack(data, size)) == NULL)
return pack_dummy(data, maxsize);
mutate(p, seed);
blob_len = pack(data, maxsize, p);
free(p);
return blob_len;
}
static void parse_mutate_flags(const char *opt, unsigned int *mutate_flags) {
const char *f;
if ((f = strchr(opt, '=')) == NULL || strlen(++f) == 0)
errx(1, "usage: --pam-u2f-mutate=<flag>");
if (strcmp(f, "seed") == 0)
*mutate_flags |= MUTATE_SEED;
else if (strcmp(f, "param") == 0)
*mutate_flags |= MUTATE_PARAM;
else if (strcmp(f, "wiredata") == 0)
*mutate_flags |= MUTATE_WIREDATA;
else
errx(1, "--pam-u2f-mutate: unknown flag '%s'", f);
}
int LLVMFuzzerInitialize(int *argc, char ***argv) {
unsigned int mutate_flags = 0;
for (int i = 0; i < *argc; i++) {
if (strncmp((*argv)[i], "--pam-u2f-mutate=", 17) == 0) {
parse_mutate_flags((*argv)[i], &mutate_flags);
}
}
if (mutate_flags)
flags = mutate_flags;
return 0;
}
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