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afl-analyze.c
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afl-analyze.c
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/*
american fuzzy lop - file format analyzer
-----------------------------------------
Written and maintained by Michal Zalewski <[email protected]>
Copyright 2016 Google Inc. All rights reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at:
http://www.apache.org/licenses/LICENSE-2.0
A nifty utility that grabs an input file and takes a stab at explaining
its structure by observing how changes to it affect the execution path.
If the output scrolls past the edge of the screen, pipe it to 'less -r'.
*/
#define AFL_MAIN
#include "config.h"
#include "types.h"
#include "debug.h"
#include "alloc-inl.h"
#include "hash.h"
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#include <signal.h>
#include <dirent.h>
#include <fcntl.h>
#include <ctype.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/resource.h>
static s32 child_pid; /* PID of the tested program */
static u8* trace_bits; /* SHM with instrumentation bitmap */
static u8 *in_file, /* Analyzer input test case */
*prog_in, /* Targeted program input file */
*target_path, /* Path to target binary */
*doc_path; /* Path to docs */
static u8 *in_data; /* Input data for analysis */
static u32 in_len, /* Input data length */
orig_cksum, /* Original checksum */
total_execs, /* Total number of execs */
exec_hangs, /* Total number of hangs */
exec_tmout = EXEC_TIMEOUT; /* Exec timeout (ms) */
static u64 mem_limit = MEM_LIMIT; /* Memory limit (MB) */
static s32 shm_id, /* ID of the SHM region */
dev_null_fd = -1; /* FD to /dev/null */
static u8 edges_only, /* Ignore hit counts? */
use_stdin = 1; /* Use stdin for program input? */
static volatile u8
stop_soon, /* Ctrl-C pressed? */
child_timed_out; /* Child timed out? */
/* Constants used for describing byte behavior. */
#define RESP_NONE 0x00 /* Changing byte is a no-op. */
#define RESP_MINOR 0x01 /* Some changes have no effect. */
#define RESP_VARIABLE 0x02 /* Changes produce variable paths. */
#define RESP_FIXED 0x03 /* Changes produce fixed patterns. */
#define RESP_LEN 0x04 /* Potential length field */
#define RESP_CKSUM 0x05 /* Potential checksum */
#define RESP_SUSPECT 0x06 /* Potential "suspect" blob */
/* Classify tuple counts. This is a slow & naive version, but good enough here. */
static u8 count_class_lookup[256] = {
[0] = 0,
[1] = 1,
[2] = 2,
[3] = 4,
[4 ... 7] = 8,
[8 ... 15] = 16,
[16 ... 31] = 32,
[32 ... 127] = 64,
[128 ... 255] = 128
};
static void classify_counts(u8* mem) {
u32 i = MAP_SIZE;
if (edges_only) {
while (i--) {
if (*mem) *mem = 1;
mem++;
}
} else {
while (i--) {
*mem = count_class_lookup[*mem];
mem++;
}
}
}
/* See if any bytes are set in the bitmap. */
static inline u8 anything_set(void) {
u32* ptr = (u32*)trace_bits;
u32 i = (MAP_SIZE >> 2);
while (i--) if (*(ptr++)) return 1;
return 0;
}
/* Get rid of shared memory and temp files (atexit handler). */
static void remove_shm(void) {
unlink(prog_in); /* Ignore errors */
shmctl(shm_id, IPC_RMID, NULL);
}
/* Configure shared memory. */
static void setup_shm(void) {
u8* shm_str;
shm_id = shmget(IPC_PRIVATE, MAP_SIZE, IPC_CREAT | IPC_EXCL | 0600);
if (shm_id < 0) PFATAL("shmget() failed");
atexit(remove_shm);
shm_str = alloc_printf("%d", shm_id);
setenv(SHM_ENV_VAR, shm_str, 1);
ck_free(shm_str);
trace_bits = shmat(shm_id, NULL, 0);
if (!trace_bits) PFATAL("shmat() failed");
}
/* Read initial file. */
static void read_initial_file(void) {
struct stat st;
s32 fd = open(in_file, O_RDONLY);
if (fd < 0) PFATAL("Unable to open '%s'", in_file);
if (fstat(fd, &st) || !st.st_size)
FATAL("Zero-sized input file.");
if (st.st_size >= TMIN_MAX_FILE)
FATAL("Input file is too large (%u MB max)", TMIN_MAX_FILE / 1024 / 1024);
in_len = st.st_size;
in_data = ck_alloc_nozero(in_len);
ck_read(fd, in_data, in_len, in_file);
close(fd);
OKF("Read %u byte%s from '%s'.", in_len, in_len == 1 ? "" : "s", in_file);
}
/* Write output file. */
static s32 write_to_file(u8* path, u8* mem, u32 len) {
s32 ret;
unlink(path); /* Ignore errors */
ret = open(path, O_RDWR | O_CREAT | O_EXCL, 0600);
if (ret < 0) PFATAL("Unable to create '%s'", path);
ck_write(ret, mem, len, path);
lseek(ret, 0, SEEK_SET);
return ret;
}
/* Handle timeout signal. */
static void handle_timeout(int sig) {
child_timed_out = 1;
if (child_pid > 0) kill(child_pid, SIGKILL);
}
/* Execute target application. Returns exec checksum, or 0 if program
times out. */
static u32 run_target(char** argv, u8* mem, u32 len, u8 first_run) {
static struct itimerval it;
int status = 0;
s32 prog_in_fd;
u32 cksum;
memset(trace_bits, 0, MAP_SIZE);
MEM_BARRIER();
prog_in_fd = write_to_file(prog_in, mem, len);
child_pid = fork();
if (child_pid < 0) PFATAL("fork() failed");
if (!child_pid) {
struct rlimit r;
if (dup2(use_stdin ? prog_in_fd : dev_null_fd, 0) < 0 ||
dup2(dev_null_fd, 1) < 0 ||
dup2(dev_null_fd, 2) < 0) {
*(u32*)trace_bits = EXEC_FAIL_SIG;
PFATAL("dup2() failed");
}
close(dev_null_fd);
close(prog_in_fd);
if (mem_limit) {
r.rlim_max = r.rlim_cur = ((rlim_t)mem_limit) << 20;
#ifdef RLIMIT_AS
setrlimit(RLIMIT_AS, &r); /* Ignore errors */
#else
setrlimit(RLIMIT_DATA, &r); /* Ignore errors */
#endif /* ^RLIMIT_AS */
}
r.rlim_max = r.rlim_cur = 0;
setrlimit(RLIMIT_CORE, &r); /* Ignore errors */
execv(target_path, argv);
*(u32*)trace_bits = EXEC_FAIL_SIG;
exit(0);
}
close(prog_in_fd);
/* Configure timeout, wait for child, cancel timeout. */
child_timed_out = 0;
it.it_value.tv_sec = (exec_tmout / 1000);
it.it_value.tv_usec = (exec_tmout % 1000) * 1000;
setitimer(ITIMER_REAL, &it, NULL);
if (waitpid(child_pid, &status, 0) <= 0) FATAL("waitpid() failed");
child_pid = 0;
it.it_value.tv_sec = 0;
it.it_value.tv_usec = 0;
setitimer(ITIMER_REAL, &it, NULL);
MEM_BARRIER();
/* Clean up bitmap, analyze exit condition, etc. */
if (*(u32*)trace_bits == EXEC_FAIL_SIG)
FATAL("Unable to execute '%s'", argv[0]);
classify_counts(trace_bits);
total_execs++;
if (stop_soon) {
SAYF(cRST cLRD "\n+++ Analysis aborted by user +++\n" cRST);
exit(1);
}
/* Always discard inputs that time out. */
if (child_timed_out) {
exec_hangs++;
return 0;
}
cksum = hash32(trace_bits, MAP_SIZE, HASH_CONST);
/* We don't actually care if the target is crashing or not,
except that when it does, the checksum should be different. */
if (WIFSIGNALED(status) ||
(WIFEXITED(status) && WEXITSTATUS(status) == MSAN_ERROR) ||
(WIFEXITED(status) && WEXITSTATUS(status))) {
cksum ^= 0xffffffff;
}
if (first_run) orig_cksum = cksum;
return cksum;
}
#ifdef USE_COLOR
/* Helper function to display a human-readable character. */
static void show_char(u8 val) {
switch (val) {
case 0 ... 32:
case 127 ... 255: SAYF("#%02x", val); break;
default: SAYF(" %c ", val);
}
}
/* Show the legend */
static void show_legend(void) {
SAYF(" " cLGR bgGRA " 01 " cRST " - no-op block "
cBLK bgLGN " 01 " cRST " - suspected length field\n"
" " cBRI bgGRA " 01 " cRST " - superficial content "
cBLK bgYEL " 01 " cRST " - suspected cksum or magic int\n"
" " cBLK bgCYA " 01 " cRST " - critical stream "
cBLK bgLRD " 01 " cRST " - suspected checksummed block\n"
" " cBLK bgMGN " 01 " cRST " - \"magic value\" section\n\n");
}
#endif /* USE_COLOR */
/* Interpret and report a pattern in the input file. */
static void dump_hex(u8* buf, u32 len, u8* b_data) {
u32 i;
for (i = 0; i < len; i++) {
#ifdef USE_COLOR
u32 rlen = 1, off;
#else
u32 rlen = 1;
#endif /* ^USE_COLOR */
u8 rtype = b_data[i] & 0x0f;
/* Look ahead to determine the length of run. */
while (i + rlen < len && (b_data[i] >> 7) == (b_data[i + rlen] >> 7)) {
if (rtype < (b_data[i + rlen] & 0x0f)) rtype = b_data[i + rlen] & 0x0f;
rlen++;
}
/* Try to do some further classification based on length & value. */
if (rtype == RESP_FIXED) {
switch (rlen) {
case 2: {
u16 val = *(u16*)(in_data + i);
/* Small integers may be length fields. */
if (val && (val <= in_len || SWAP16(val) <= in_len)) {
rtype = RESP_LEN;
break;
}
/* Uniform integers may be checksums. */
if (val && abs(in_data[i] - in_data[i + 1]) > 32) {
rtype = RESP_CKSUM;
break;
}
break;
}
case 4: {
u32 val = *(u32*)(in_data + i);
/* Small integers may be length fields. */
if (val && (val <= in_len || SWAP32(val) <= in_len)) {
rtype = RESP_LEN;
break;
}
/* Uniform integers may be checksums. */
if (val && (in_data[i] >> 7 != in_data[i + 1] >> 7 ||
in_data[i] >> 7 != in_data[i + 2] >> 7 ||
in_data[i] >> 7 != in_data[i + 3] >> 7)) {
rtype = RESP_CKSUM;
break;
}
break;
}
case 1: case 3: case 5 ... MAX_AUTO_EXTRA - 1: break;
default: rtype = RESP_SUSPECT;
}
}
/* Print out the entire run. */
#ifdef USE_COLOR
for (off = 0; off < rlen; off++) {
/* Every 16 digits, display offset. */
if (!((i + off) % 16)) {
if (off) SAYF(cRST cLCY ">");
SAYF(cRST cGRA "%s[%06u] " cRST, (i + off) ? "\n" : "", i + off);
}
switch (rtype) {
case RESP_NONE: SAYF(cLGR bgGRA); break;
case RESP_MINOR: SAYF(cBRI bgGRA); break;
case RESP_VARIABLE: SAYF(cBLK bgCYA); break;
case RESP_FIXED: SAYF(cBLK bgMGN); break;
case RESP_LEN: SAYF(cBLK bgLGN); break;
case RESP_CKSUM: SAYF(cBLK bgYEL); break;
case RESP_SUSPECT: SAYF(cBLK bgLRD); break;
}
show_char(in_data[i + off]);
if (off != rlen - 1 && (i + off + 1) % 16) SAYF(" "); else SAYF(cRST " ");
}
#else
SAYF(" Offset %u, length %u: ", i, rlen);
switch (rtype) {
case RESP_NONE: SAYF("no-op block\n"); break;
case RESP_MINOR: SAYF("superficial content\n"); break;
case RESP_VARIABLE: SAYF("critical stream\n"); break;
case RESP_FIXED: SAYF("\"magic value\" section\n"); break;
case RESP_LEN: SAYF("suspected length field\n"); break;
case RESP_CKSUM: SAYF("suspected cksum or magic int\n"); break;
case RESP_SUSPECT: SAYF("suspected checksummed block\n"); break;
}
#endif /* ^USE_COLOR */
i += rlen - 1;
}
#ifdef USE_COLOR
SAYF(cRST "\n");
#endif /* USE_COLOR */
}
/* Actually analyze! */
static void analyze(char** argv) {
u32 i;
u32 boring_len = 0, prev_xff = 0, prev_x01 = 0, prev_s10 = 0, prev_a10 = 0;
u8* b_data = ck_alloc(in_len + 1);
u8 seq_byte = 0;
b_data[in_len] = 0xff; /* Intentional terminator. */
ACTF("Analyzing input file (this may take a while)...\n");
#ifdef USE_COLOR
show_legend();
#endif /* USE_COLOR */
for (i = 0; i < in_len; i++) {
u32 xor_ff, xor_01, sub_10, add_10;
u8 xff_orig, x01_orig, s10_orig, a10_orig;
/* Perform walking byte adjustments across the file. We perform four
operations designed to elicit some response from the underlying
code. */
in_data[i] ^= 0xff;
xor_ff = run_target(argv, in_data, in_len, 0);
in_data[i] ^= 0xfe;
xor_01 = run_target(argv, in_data, in_len, 0);
in_data[i] = (in_data[i] ^ 0x01) - 0x10;
sub_10 = run_target(argv, in_data, in_len, 0);
in_data[i] += 0x20;
add_10 = run_target(argv, in_data, in_len, 0);
in_data[i] -= 0x10;
/* Classify current behavior. */
xff_orig = (xor_ff == orig_cksum);
x01_orig = (xor_01 == orig_cksum);
s10_orig = (sub_10 == orig_cksum);
a10_orig = (add_10 == orig_cksum);
if (xff_orig && x01_orig && s10_orig && a10_orig) {
b_data[i] = RESP_NONE;
boring_len++;
} else if (xff_orig || x01_orig || s10_orig || a10_orig) {
b_data[i] = RESP_MINOR;
boring_len++;
} else if (xor_ff == xor_01 && xor_ff == sub_10 && xor_ff == add_10) {
b_data[i] = RESP_FIXED;
} else b_data[i] = RESP_VARIABLE;
/* When all checksums change, flip most significant bit of b_data. */
if (prev_xff != xor_ff && prev_x01 != xor_01 &&
prev_s10 != sub_10 && prev_a10 != add_10) seq_byte ^= 0x80;
b_data[i] |= seq_byte;
prev_xff = xor_ff;
prev_x01 = xor_01;
prev_s10 = sub_10;
prev_a10 = add_10;
}
dump_hex(in_data, in_len, b_data);
SAYF("\n");
OKF("Analysis complete. Interesting bits: %0.02f%% of the input file.",
100.0 - ((double)boring_len * 100) / in_len);
if (exec_hangs)
WARNF(cLRD "Encountered %u timeouts - results may be skewed." cRST,
exec_hangs);
ck_free(b_data);
}
/* Handle Ctrl-C and the like. */
static void handle_stop_sig(int sig) {
stop_soon = 1;
if (child_pid > 0) kill(child_pid, SIGKILL);
}
/* Do basic preparations - persistent fds, filenames, etc. */
static void set_up_environment(void) {
u8* x;
dev_null_fd = open("/dev/null", O_RDWR);
if (dev_null_fd < 0) PFATAL("Unable to open /dev/null");
if (!prog_in) {
u8* use_dir = ".";
if (!access(use_dir, R_OK | W_OK | X_OK)) {
use_dir = getenv("TMPDIR");
if (!use_dir) use_dir = "/tmp";
prog_in = alloc_printf("%s/.afl-tmin-temp-%u", use_dir, getpid());
}
}
/* Set sane defaults... */
x = getenv("ASAN_OPTIONS");
if (x) {
if (!strstr(x, "abort_on_error=1"))
FATAL("Custom ASAN_OPTIONS set without abort_on_error=1 - please fix!");
if (!strstr(x, "symbolize=0"))
FATAL("Custom ASAN_OPTIONS set without symbolize=0 - please fix!");
}
x = getenv("MSAN_OPTIONS");
if (x) {
if (!strstr(x, "exit_code=" STRINGIFY(MSAN_ERROR)))
FATAL("Custom MSAN_OPTIONS set without exit_code="
STRINGIFY(MSAN_ERROR) " - please fix!");
if (!strstr(x, "symbolize=0"))
FATAL("Custom MSAN_OPTIONS set without symbolize=0 - please fix!");
}
setenv("ASAN_OPTIONS", "abort_on_error=1:"
"detect_leaks=0:"
"symbolize=0:"
"allocator_may_return_null=1", 0);
setenv("MSAN_OPTIONS", "exit_code=" STRINGIFY(MSAN_ERROR) ":"
"symbolize=0:"
"abort_on_error=1:"
"allocator_may_return_null=1:"
"msan_track_origins=0", 0);
if (getenv("AFL_PRELOAD")) {
setenv("LD_PRELOAD", getenv("AFL_PRELOAD"), 1);
setenv("DYLD_INSERT_LIBRARIES", getenv("AFL_PRELOAD"), 1);
}
}
/* Setup signal handlers, duh. */
static void setup_signal_handlers(void) {
struct sigaction sa;
sa.sa_handler = NULL;
sa.sa_flags = SA_RESTART;
sa.sa_sigaction = NULL;
sigemptyset(&sa.sa_mask);
/* Various ways of saying "stop". */
sa.sa_handler = handle_stop_sig;
sigaction(SIGHUP, &sa, NULL);
sigaction(SIGINT, &sa, NULL);
sigaction(SIGTERM, &sa, NULL);
/* Exec timeout notifications. */
sa.sa_handler = handle_timeout;
sigaction(SIGALRM, &sa, NULL);
}
/* Detect @@ in args. */
static void detect_file_args(char** argv) {
u32 i = 0;
u8* cwd = getcwd(NULL, 0);
if (!cwd) PFATAL("getcwd() failed");
while (argv[i]) {
u8* aa_loc = strstr(argv[i], "@@");
if (aa_loc) {
u8 *aa_subst, *n_arg;
/* Be sure that we're always using fully-qualified paths. */
if (prog_in[0] == '/') aa_subst = prog_in;
else aa_subst = alloc_printf("%s/%s", cwd, prog_in);
/* Construct a replacement argv value. */
*aa_loc = 0;
n_arg = alloc_printf("%s%s%s", argv[i], aa_subst, aa_loc + 2);
argv[i] = n_arg;
*aa_loc = '@';
if (prog_in[0] != '/') ck_free(aa_subst);
}
i++;
}
free(cwd); /* not tracked */
}
/* Display usage hints. */
static void usage(u8* argv0) {
SAYF("\n%s [ options ] -- /path/to/target_app [ ... ]\n\n"
"Required parameters:\n\n"
" -i file - input test case to be analyzed by the tool\n"
"Execution control settings:\n\n"
" -f file - input file read by the tested program (stdin)\n"
" -t msec - timeout for each run (%u ms)\n"
" -m megs - memory limit for child process (%u MB)\n"
" -Q - use binary-only instrumentation (QEMU mode)\n\n"
"Analysis settings:\n\n"
" -e - look for edge coverage only, ignore hit counts\n\n"
"For additional tips, please consult %s/README.\n\n",
argv0, EXEC_TIMEOUT, MEM_LIMIT, doc_path);
exit(1);
}
/* Find binary. */
static void find_binary(u8* fname) {
u8* env_path = 0;
struct stat st;
if (strchr(fname, '/') || !(env_path = getenv("PATH"))) {
target_path = ck_strdup(fname);
if (stat(target_path, &st) || !S_ISREG(st.st_mode) ||
!(st.st_mode & 0111) || st.st_size < 4)
FATAL("Program '%s' not found or not executable", fname);
} else {
while (env_path) {
u8 *cur_elem, *delim = strchr(env_path, ':');
if (delim) {
cur_elem = ck_alloc(delim - env_path + 1);
memcpy(cur_elem, env_path, delim - env_path);
delim++;
} else cur_elem = ck_strdup(env_path);
env_path = delim;
if (cur_elem[0])
target_path = alloc_printf("%s/%s", cur_elem, fname);
else
target_path = ck_strdup(fname);
ck_free(cur_elem);
if (!stat(target_path, &st) && S_ISREG(st.st_mode) &&
(st.st_mode & 0111) && st.st_size >= 4) break;
ck_free(target_path);
target_path = 0;
}
if (!target_path) FATAL("Program '%s' not found or not executable", fname);
}
}
/* Fix up argv for QEMU. */
static char** get_qemu_argv(u8* own_loc, char** argv, int argc) {
char** new_argv = ck_alloc(sizeof(char*) * (argc + 4));
u8 *tmp, *cp, *rsl, *own_copy;
memcpy(new_argv + 3, argv + 1, sizeof(char*) * argc);
/* Now we need to actually find qemu for argv[0]. */
new_argv[2] = target_path;
new_argv[1] = "--";
tmp = getenv("AFL_PATH");
if (tmp) {
cp = alloc_printf("%s/afl-qemu-trace", tmp);
if (access(cp, X_OK))
FATAL("Unable to find '%s'", tmp);
target_path = new_argv[0] = cp;
return new_argv;
}
own_copy = ck_strdup(own_loc);
rsl = strrchr(own_copy, '/');
if (rsl) {
*rsl = 0;
cp = alloc_printf("%s/afl-qemu-trace", own_copy);
ck_free(own_copy);
if (!access(cp, X_OK)) {
target_path = new_argv[0] = cp;
return new_argv;
}
} else ck_free(own_copy);
if (!access(BIN_PATH "/afl-qemu-trace", X_OK)) {
target_path = new_argv[0] = BIN_PATH "/afl-qemu-trace";
return new_argv;
}
FATAL("Unable to find 'afl-qemu-trace'.");
}
/* Main entry point */
int main(int argc, char** argv) {
s32 opt;
u8 mem_limit_given = 0, timeout_given = 0, qemu_mode = 0;
char** use_argv;
doc_path = access(DOC_PATH, F_OK) ? "docs" : DOC_PATH;
SAYF(cCYA "afl-analyze " cBRI VERSION cRST " by <[email protected]>\n");
while ((opt = getopt(argc,argv,"+i:f:m:t:eQ")) > 0)
switch (opt) {
case 'i':
if (in_file) FATAL("Multiple -i options not supported");
in_file = optarg;
break;
case 'f':
if (prog_in) FATAL("Multiple -f options not supported");
use_stdin = 0;
prog_in = optarg;
break;
case 'e':
if (edges_only) FATAL("Multiple -e options not supported");
edges_only = 1;
break;
case 'm': {
u8 suffix = 'M';
if (mem_limit_given) FATAL("Multiple -m options not supported");
mem_limit_given = 1;
if (!strcmp(optarg, "none")) {
mem_limit = 0;
break;
}
if (sscanf(optarg, "%llu%c", &mem_limit, &suffix) < 1 ||
optarg[0] == '-') FATAL("Bad syntax used for -m");
switch (suffix) {
case 'T': mem_limit *= 1024 * 1024; break;
case 'G': mem_limit *= 1024; break;
case 'k': mem_limit /= 1024; break;
case 'M': break;
default: FATAL("Unsupported suffix or bad syntax for -m");
}
if (mem_limit < 5) FATAL("Dangerously low value of -m");
if (sizeof(rlim_t) == 4 && mem_limit > 2000)
FATAL("Value of -m out of range on 32-bit systems");
}
break;