libselinux: add selabel_file(5) fuzzer

Add two fuzzer 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>
---
v2: add patch

libselinux/fuzz/selabel_file_compiled-fuzzer.c

@@ -0,0 +1,279 @@
+#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);
+
+	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;
+}