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afl-analyze.c
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afl-analyze.c
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/*
Copyright 2016 Google LLC 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
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
/*
american fuzzy lop - file format analyzer
-----------------------------------------
Written and maintained by Michal Zalewski <lcamtuf@google.com>
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 "android-ashmem.h"
#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_hex_offsets, /* Show hex offsets? */
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 == (void *)-1) 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 ">");
if (use_hex_offsets)
SAYF(cRST cGRA "%s[%06x] " cRST, (i + off) ? "\n" : "", i + off);
else
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
if (use_hex_offsets)
SAYF(" Offset %x, length %u: ", i, rlen);
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-analyze-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"
"Other stuff:\n\n"
" -V - show version number and exit\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;
/* Workaround for a QEMU stability glitch. */
setenv("QEMU_LOG", "nochain", 1);
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 <lcamtuf@google.com>\n");
while ((opt = getopt(argc,argv,"+i:f:m:t:eQV")) > 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;