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ossfuzz: Improvements to json_load_dump_fuzzer

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Add in diagnostics to json_load_dump_fuzzer so that if FUZZ_VERBOSE is
defined in the environment, additional debug information about the
current test case is output to stderr.

Replace json_dumps by json_dump_callback so that memory is not exhausted
by excessively nested json objects.
This commit is contained in:
Max Dymond 2019-07-24 10:10:24 +01:00
parent 1ac79b2558
commit 66dec35c8c
No known key found for this signature in database
GPG Key ID: 12A8D9E2219BD5FA
1 changed files with 64 additions and 6 deletions
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68
test/ossfuzz/json_load_dump_fuzzer.cc
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@ -1,12 +1,37 @@
#include <stdint.h> #include <stdint.h>
#include <stdlib.h>
#include <sys/types.h> #include <sys/types.h>
#include <inttypes.h>
#include "jansson.h" #include "jansson.h"
static int enable_diags;
#define FUZZ_DEBUG(FMT, ...) \
if (enable_diags) \
{ \
fprintf(stderr, FMT, ##__VA_ARGS__); \
fprintf(stderr, "\n"); \
}
static int json_dump_counter(const char *buffer, size_t size, void *data)
{
uint64_t *counter = reinterpret_cast<uint64_t *>(data);
*counter += size;
return 0;
}
extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
{ {
json_error_t error; json_error_t error;
// Enable or disable diagnostics based on the FUZZ_VERBOSE environment flag.
enable_diags = (getenv("FUZZ_VERBOSE") != NULL);
FUZZ_DEBUG("Input data length: %zd", size);
if (size < sizeof(size_t) + sizeof(size_t)) if (size < sizeof(size_t) + sizeof(size_t))
{ {
return 0; return 0;
@ -17,11 +42,45 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
data += sizeof(size_t); data += sizeof(size_t);
size -= sizeof(size_t); size -= sizeof(size_t);
FUZZ_DEBUG("load_flags: 0x%zx\n"
"& JSON_REJECT_DUPLICATES = 0x%zx\n"
"& JSON_DECODE_ANY = 0x%zx\n"
"& JSON_DISABLE_EOF_CHECK = 0x%zx\n"
"& JSON_DECODE_INT_AS_REAL = 0x%zx\n"
"& JSON_ALLOW_NUL = 0x%zx\n",
load_flags,
load_flags & JSON_REJECT_DUPLICATES,
load_flags & JSON_DECODE_ANY,
load_flags & JSON_DISABLE_EOF_CHECK,
load_flags & JSON_DECODE_INT_AS_REAL,
load_flags & JSON_ALLOW_NUL);
// Use the next sizeof(size_t) bytes as dump flags. // Use the next sizeof(size_t) bytes as dump flags.
size_t dump_flags = *(const size_t*)data; size_t dump_flags = *(const size_t*)data;
data += sizeof(size_t); data += sizeof(size_t);
size -= sizeof(size_t); size -= sizeof(size_t);
FUZZ_DEBUG("dump_flags: 0x%zx\n"
"& JSON_MAX_INDENT = 0x%zx\n"
"& JSON_COMPACT = 0x%zx\n"
"& JSON_ENSURE_ASCII = 0x%zx\n"
"& JSON_SORT_KEYS = 0x%zx\n"
"& JSON_PRESERVE_ORDER = 0x%zx\n"
"& JSON_ENCODE_ANY = 0x%zx\n"
"& JSON_ESCAPE_SLASH = 0x%zx\n"
"& JSON_REAL_PRECISION = 0x%zx\n"
"& JSON_EMBED = 0x%zx\n",
dump_flags,
dump_flags & JSON_MAX_INDENT,
dump_flags & JSON_COMPACT,
dump_flags & JSON_ENSURE_ASCII,
dump_flags & JSON_SORT_KEYS,
dump_flags & JSON_PRESERVE_ORDER,
dump_flags & JSON_ENCODE_ANY,
dump_flags & JSON_ESCAPE_SLASH,
((dump_flags >> 11) & 0x1F) << 11,
dump_flags & JSON_EMBED);
// Attempt to load the remainder of the data with the given load flags. // Attempt to load the remainder of the data with the given load flags.
const char* text = reinterpret_cast<const char *>(data); const char* text = reinterpret_cast<const char *>(data);
json_t* jobj = json_loadb(text, size, load_flags, &error); json_t* jobj = json_loadb(text, size, load_flags, &error);
@ -32,11 +91,10 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
} }
// Attempt to dump the loaded json object with the given dump flags. // Attempt to dump the loaded json object with the given dump flags.
char* out = json_dumps(jobj, dump_flags); uint64_t counter = 0;
if (out)
{ json_dump_callback(jobj, json_dump_counter, &counter, dump_flags);
free(out); FUZZ_DEBUG("Counter function counted %" PRIu64 " bytes.", counter);
}
if (jobj) if (jobj)
{ {