libselinux: add selabel_file(5) fuzzer

Add two fuzzers reading and performing lookup on selabel_file(5)
databases.  One fuzzer takes input in form of a textual fcontext
definition, the other one takes compiled fcontexts definitions.  The
lookup key and whether to lookup any or a specific file type is also
part of the generated input.

CC: Evgeny Vereshchagin <evverx@gmail.com>
Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Acked-by: James Carter <jwcart2@gmail.com>
This commit is contained in:
Christian Göttsche 2024-11-05 19:33:18 +01:00 committed by James Carter
parent daa3e6e9ba
commit 8997f54322
6 changed files with 566 additions and 20 deletions

0
libselinux/fuzz/input Normal file
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@ -0,0 +1,281 @@
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>
#include <selinux/label.h>
#include "../src/label_file.h"
extern int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
#define MEMFD_FILE_NAME "file_contexts"
#define CTRL_PARTIAL (1U << 0)
#define CTRL_FIND_ALL (1U << 1)
#define CTRL_MODE (1U << 2)
__attribute__ ((format(printf, 2, 3)))
static int null_log(int type __attribute__((unused)), const char *fmt __attribute__((unused)), ...)
{
return 0;
}
static int validate_context(char **ctxp)
{
assert(strcmp(*ctxp, "<<none>>") != 0);
if (*ctxp[0] == '\0') {
errno = EINVAL;
return -1;
}
return 0;
}
static int write_full(int fd, const void *data, size_t size)
{
ssize_t rc;
const unsigned char *p = data;
while (size > 0) {
rc = write(fd, p, size);
if (rc == -1) {
if (errno == EINTR)
continue;
return -1;
}
p += rc;
size -= rc;
}
return 0;
}
static FILE* convert_data(const uint8_t *data, size_t size)
{
FILE* stream;
int fd, rc;
fd = memfd_create(MEMFD_FILE_NAME, MFD_CLOEXEC);
if (fd == -1)
return NULL;
rc = write_full(fd, data, size);
if (rc == -1) {
close(fd);
return NULL;
}
stream = fdopen(fd, "r");
if (!stream) {
close(fd);
return NULL;
}
rc = fseek(stream, 0L, SEEK_SET);
if (rc == -1) {
fclose(stream);
return NULL;
}
return stream;
}
int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
{
struct selabel_handle rec;
struct saved_data sdata = {};
struct spec_node *root = NULL;
FILE* fp = NULL;
struct lookup_result *result = NULL;
uint8_t control;
uint8_t *fcontext_data1 = NULL, *fcontext_data2 = NULL, *fcontext_data3 = NULL;
char *key = NULL;
size_t fcontext_data1_len, fcontext_data2_len, fcontext_data3_len, key_len;
bool partial, find_all;
mode_t mode;
int rc;
/*
* Treat first byte as control byte, whether to use partial mode, find all matches or mode to lookup
*/
if (size == 0)
return 0;
control = data[0];
data++;
size--;
if (control & ~(CTRL_PARTIAL | CTRL_FIND_ALL | CTRL_MODE))
return 0;
partial = control & CTRL_PARTIAL;
find_all = control & CTRL_FIND_ALL;
/* S_IFSOCK has the highest integer value */
mode = (control & CTRL_MODE) ? S_IFSOCK : 0;
/*
* Split the fuzzer input into up to four pieces: one to three compiled fcontext
* definitions (to mimic file_contexts, file_contexts.homedirs and file_contexts.local,
* and the lookup key
*/
const unsigned char separator[4] = { 0xde, 0xad, 0xbe, 0xef };
const uint8_t *sep = memmem(data, size, separator, 4);
if (!sep || sep == data)
return 0;
fcontext_data1_len = sep - data;
fcontext_data1 = malloc(fcontext_data1_len);
if (!fcontext_data1)
goto cleanup;
memcpy(fcontext_data1, data, fcontext_data1_len);
data += fcontext_data1_len + 4;
size -= fcontext_data1_len + 4;
sep = memmem(data, size, separator, 4);
if (sep) {
fcontext_data2_len = sep - data;
fcontext_data2 = malloc(fcontext_data2_len);
if (!fcontext_data2)
goto cleanup;
memcpy(fcontext_data2, data, fcontext_data2_len);
data += fcontext_data2_len + 4;
size -= fcontext_data2_len + 4;
}
sep = memmem(data, size, separator, 4);
if (sep) {
fcontext_data3_len = sep - data;
fcontext_data3 = malloc(fcontext_data3_len);
if (!fcontext_data3)
goto cleanup;
memcpy(fcontext_data3, data, fcontext_data3_len);
data += fcontext_data3_len + 4;
size -= fcontext_data3_len + 4;
}
key_len = size;
key = malloc(key_len + 1);
if (!key)
goto cleanup;
memcpy(key, data, key_len);
key[key_len] = '\0';
/*
* Mock selabel handle
*/
rec = (struct selabel_handle) {
.backend = SELABEL_CTX_FILE,
.validating = 1,
.data = &sdata,
};
selinux_set_callback(SELINUX_CB_LOG, (union selinux_callback) { .func_log = &null_log });
/* validate to pre-compile regular expressions */
selinux_set_callback(SELINUX_CB_VALIDATE, (union selinux_callback) { .func_validate = &validate_context });
root = calloc(1, sizeof(*root));
if (!root)
goto cleanup;
sdata.root = root;
fp = convert_data(fcontext_data1, fcontext_data1_len);
if (!fp)
goto cleanup;
errno = 0;
rc = load_mmap(fp, fcontext_data1_len, &rec, MEMFD_FILE_NAME);
if (rc) {
assert(errno != 0);
goto cleanup;
}
fclose(fp);
fp = convert_data(fcontext_data2, fcontext_data2_len);
if (!fp)
goto cleanup;
errno = 0;
rc = load_mmap(fp, fcontext_data2_len, &rec, MEMFD_FILE_NAME);
if (rc) {
assert(errno != 0);
goto cleanup;
}
fclose(fp);
fp = convert_data(fcontext_data3, fcontext_data3_len);
if (!fp)
goto cleanup;
errno = 0;
rc = load_mmap(fp, fcontext_data3_len, &rec, MEMFD_FILE_NAME);
if (rc) {
assert(errno != 0);
goto cleanup;
}
sort_specs(&sdata);
assert(cmp(&rec, &rec) == SELABEL_EQUAL);
errno = 0;
result = lookup_all(&rec, key, mode, partial, find_all);
if (!result)
assert(errno != 0);
for (const struct lookup_result *res = result; res; res = res->next) {
assert(res->regex_str);
assert(res->regex_str[0] != '\0');
assert(res->lr->ctx_raw);
assert(res->lr->ctx_raw[0] != '\0');
assert(strcmp(res->lr->ctx_raw, "<<none>>") != 0);
assert(!res->lr->ctx_trans);
assert(res->lr->validated);
assert(res->prefix_len <= strlen(res->regex_str));
}
cleanup:
free_lookup_result(result);
if (fp)
fclose(fp);
if (sdata.root) {
free_spec_node(sdata.root);
free(sdata.root);
}
{
struct mmap_area *area, *last_area;
area = sdata.mmap_areas;
while (area) {
rc = munmap(area->addr, area->len);
assert(rc == 0);
last_area = area;
area = area->next;
free(last_area);
}
}
free(key);
free(fcontext_data3);
free(fcontext_data2);
free(fcontext_data1);
/* Non-zero return values are reserved for future use. */
return 0;
}

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@ -0,0 +1,225 @@
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>
#include <selinux/label.h>
#include "../src/label_file.h"
extern int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
#define MEMFD_FILE_NAME "file_contexts"
#define CTRL_PARTIAL (1U << 0)
#define CTRL_FIND_ALL (1U << 1)
#define CTRL_MODE (1U << 2)
__attribute__ ((format(printf, 2, 3)))
static int null_log(int type __attribute__((unused)), const char *fmt __attribute__((unused)), ...)
{
return 0;
}
static int validate_context(char **ctxp)
{
assert(strcmp(*ctxp, "<<none>>") != 0);
if (*ctxp[0] == '\0') {
errno = EINVAL;
return -1;
}
return 0;
}
static int write_full(int fd, const void *data, size_t size)
{
ssize_t rc;
const unsigned char *p = data;
while (size > 0) {
rc = write(fd, p, size);
if (rc == -1) {
if (errno == EINTR)
continue;
return -1;
}
p += rc;
size -= rc;
}
return 0;
}
static FILE* convert_data(const uint8_t *data, size_t size)
{
FILE* stream;
int fd, rc;
fd = memfd_create(MEMFD_FILE_NAME, MFD_CLOEXEC);
if (fd == -1)
return NULL;
rc = write_full(fd, data, size);
if (rc == -1) {
close(fd);
return NULL;
}
stream = fdopen(fd, "r");
if (!stream) {
close(fd);
return NULL;
}
rc = fseek(stream, 0L, SEEK_SET);
if (rc == -1) {
fclose(stream);
return NULL;
}
return stream;
}
int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
{
struct selabel_handle rec;
struct saved_data sdata = {};
struct spec_node *root = NULL;
FILE* fp = NULL;
struct lookup_result *result = NULL;
uint8_t control;
uint8_t *fcontext_data = NULL;
char *key = NULL;
size_t fcontext_data_len, key_len;
bool partial, find_all;
mode_t mode;
int rc;
/*
* Treat first byte as control byte, whether to use partial mode, find all matches or mode to lookup
*/
if (size == 0)
return 0;
control = data[0];
data++;
size--;
if (control & ~(CTRL_PARTIAL | CTRL_FIND_ALL | CTRL_MODE))
return 0;
partial = control & CTRL_PARTIAL;
find_all = control & CTRL_FIND_ALL;
/* S_IFSOCK has the highest integer value */
mode = (control & CTRL_MODE) ? S_IFSOCK : 0;
/*
* Split the fuzzer input into two pieces: the textual fcontext definition and the lookup key
*/
const unsigned char separator[4] = { 0xde, 0xad, 0xbe, 0xef };
const uint8_t *sep = memmem(data, size, separator, 4);
if (!sep || sep == data)
return 0;
fcontext_data_len = sep - data;
fcontext_data = malloc(fcontext_data_len);
if (!fcontext_data)
goto cleanup;
memcpy(fcontext_data, data, fcontext_data_len);
key_len = size - fcontext_data_len - 4;
key = malloc(key_len + 1);
if (!key)
goto cleanup;
memcpy(key, sep + 4, key_len);
key[key_len] = '\0';
/*
* Mock selabel handle
*/
rec = (struct selabel_handle) {
.backend = SELABEL_CTX_FILE,
.validating = 1,
.data = &sdata,
};
selinux_set_callback(SELINUX_CB_LOG, (union selinux_callback) { .func_log = &null_log });
/* validate to pre-compile regular expressions */
selinux_set_callback(SELINUX_CB_VALIDATE, (union selinux_callback) { .func_validate = &validate_context });
root = calloc(1, sizeof(*root));
if (!root)
goto cleanup;
sdata.root = root;
fp = convert_data(fcontext_data, fcontext_data_len);
if (!fp)
goto cleanup;
errno = 0;
rc = process_text_file(fp, /*prefix=*/ NULL, &rec, MEMFD_FILE_NAME);
if (rc) {
assert(errno != 0);
goto cleanup;
}
sort_specs(&sdata);
assert(cmp(&rec, &rec) == SELABEL_EQUAL);
errno = 0;
result = lookup_all(&rec, key, mode, partial, find_all);
if (!result)
assert(errno != 0);
for (const struct lookup_result *res = result; res; res = res->next) {
assert(res->regex_str);
assert(res->regex_str[0] != '\0');
assert(res->lr->ctx_raw);
assert(res->lr->ctx_raw[0] != '\0');
assert(strcmp(res->lr->ctx_raw, "<<none>>") != 0);
assert(!res->lr->ctx_trans);
assert(res->lr->validated);
assert(res->prefix_len <= strlen(res->regex_str));
}
cleanup:
free_lookup_result(result);
if (fp)
fclose(fp);
if (sdata.root) {
free_spec_node(sdata.root);
free(sdata.root);
}
{
struct mmap_area *area, *last_area;
area = sdata.mmap_areas;
while (area) {
rc = munmap(area->addr, area->len);
assert(rc == 0);
last_area = area;
area = area->next;
free(last_area);
}
}
free(key);
free(fcontext_data);
/* Non-zero return values are reserved for future use. */
return 0;
}

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@ -27,6 +27,13 @@
#include "label_file.h"
#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
# define FUZZ_EXTERN
#else
# define FUZZ_EXTERN static
#endif /* FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION */
/*
* Warn about duplicate specifications.
*/
@ -114,7 +121,7 @@ static int nodups_spec_node(const struct spec_node *node, const char *path)
return rc;
}
static int process_text_file(FILE *fp, const char *prefix,
FUZZ_EXTERN int process_text_file(FILE *fp, const char *prefix,
struct selabel_handle *rec, const char *path)
{
int rc;
@ -720,7 +727,7 @@ static int load_mmap_spec_node(struct mmap_area *mmap_area, const char *path, bo
return 0;
}
static int load_mmap(FILE *fp, const size_t len, struct selabel_handle *rec,
FUZZ_EXTERN int load_mmap(FILE *fp, const size_t len, struct selabel_handle *rec,
const char *path)
{
struct saved_data *data = rec->data;
@ -1449,16 +1456,7 @@ static uint32_t search_literal_spec(const struct literal_spec *array, uint32_t s
return (uint32_t)-1;
}
struct lookup_result {
const char *regex_str;
struct selabel_lookup_rec *lr;
uint16_t prefix_len;
uint8_t file_kind;
bool has_meta_chars;
struct lookup_result *next;
};
static void free_lookup_result(struct lookup_result *result)
FUZZ_EXTERN void free_lookup_result(struct lookup_result *result)
{
struct lookup_result *tmp;
@ -1690,7 +1688,7 @@ static uint8_t mode_to_file_kind(int type) {
// Finds all the matches of |key| in the given context. Returns the result in
// the allocated array and updates the match count. If match_count is NULL,
// stops early once the 1st match is found.
static struct lookup_result *lookup_all(struct selabel_handle *rec,
FUZZ_EXTERN struct lookup_result *lookup_all(struct selabel_handle *rec,
const char *key,
int type,
bool partial,
@ -2283,7 +2281,7 @@ static enum selabel_cmp_result spec_node_cmp(const struct spec_node *node1, cons
return result;
}
static enum selabel_cmp_result cmp(const struct selabel_handle *h1, const struct selabel_handle *h2)
FUZZ_EXTERN enum selabel_cmp_result cmp(const struct selabel_handle *h1, const struct selabel_handle *h2)
{
const struct saved_data *data1, *data2;

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@ -50,6 +50,23 @@
#define LABEL_FILE_KIND_LNK 6
#define LABEL_FILE_KIND_REG 7
/* Only exported for fuzzing */
struct lookup_result {
const char *regex_str;
struct selabel_lookup_rec *lr;
uint16_t prefix_len;
uint8_t file_kind;
bool has_meta_chars;
struct lookup_result *next;
};
#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
extern int load_mmap(FILE *fp, const size_t len, struct selabel_handle *rec, const char *path);
extern int process_text_file(FILE *fp, const char *prefix, struct selabel_handle *rec, const char *path);
extern void free_lookup_result(struct lookup_result *result);
extern struct lookup_result *lookup_all(struct selabel_handle *rec, const char *key, int type, bool partial, bool find_all);
extern enum selabel_cmp_result cmp(const struct selabel_handle *h1, const struct selabel_handle *h2);
#endif /* FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION */
struct selabel_sub {
char *src;
unsigned int slen;

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@ -44,10 +44,13 @@ export LIB_FUZZING_ENGINE=${LIB_FUZZING_ENGINE:--fsanitize=fuzzer}
rm -rf "$DESTDIR"
make -C libsepol clean
make -C libselinux clean
# LIBSO and LIBMAP shouldn't be expanded here because their values are unknown until Makefile
# has been read by make
# shellcheck disable=SC2016
make -C libsepol V=1 LD_SONAME_FLAGS='-soname,$(LIBSO),--version-script=$(LIBMAP)' -j"$(nproc)" install
# shellcheck disable=SC2016
make -C libselinux V=1 LD_SONAME_FLAGS='-soname,$(LIBSO),--version-script=libselinux.map' -j"$(nproc)" install
## secilc fuzzer ##
@ -84,3 +87,25 @@ $CXX $CXXFLAGS $LIB_FUZZING_ENGINE checkpolicy-fuzzer.o checkpolicy/*.o "$DESTDI
zip -j "$OUT/checkpolicy-fuzzer_seed_corpus.zip" checkpolicy/fuzz/min_pol.mls.conf
cp checkpolicy/fuzz/checkpolicy-fuzzer.dict "$OUT/"
## selabel-file text fcontext based fuzzer ##
# CFLAGS, CXXFLAGS and LIB_FUZZING_ENGINE have to be split to be accepted by
# the compiler/linker so they shouldn't be quoted
# shellcheck disable=SC2086
$CC $CFLAGS -DUSE_PCRE2 -DPCRE2_CODE_UNIT_WIDTH=8 -c -o selabel_file_text-fuzzer.o libselinux/fuzz/selabel_file_text-fuzzer.c
# shellcheck disable=SC2086
$CXX $CXXFLAGS $LIB_FUZZING_ENGINE selabel_file_text-fuzzer.o "$DESTDIR/usr/lib/libselinux.a" -lpcre2-8 -o "$OUT/selabel_file_text-fuzzer"
zip -j "$OUT/selabel_file_text-fuzzer_seed_corpus.zip" libselinux/fuzz/input
## selabel-file compiled fcontext based fuzzer ##
# CFLAGS, CXXFLAGS and LIB_FUZZING_ENGINE have to be split to be accepted by
# the compiler/linker so they shouldn't be quoted
# shellcheck disable=SC2086
$CC $CFLAGS -DUSE_PCRE2 -DPCRE2_CODE_UNIT_WIDTH=8 -c -o selabel_file_compiled-fuzzer.o libselinux/fuzz/selabel_file_compiled-fuzzer.c
# shellcheck disable=SC2086
$CXX $CXXFLAGS $LIB_FUZZING_ENGINE selabel_file_compiled-fuzzer.o "$DESTDIR/usr/lib/libselinux.a" -lpcre2-8 -o "$OUT/selabel_file_compiled-fuzzer"
zip -j "$OUT/selabel_file_compiled-fuzzer_seed_corpus.zip" libselinux/fuzz/input