| /* |
| american fuzzy lop++ - forkserver code |
| -------------------------------------- |
| |
| Originally written by Michal Zalewski |
| |
| Forkserver design by Jann Horn <jannhorn@googlemail.com> |
| |
| Now maintained by Marc Heuse <mh@mh-sec.de>, |
| Heiko Eißfeldt <heiko.eissfeldt@hexco.de> and |
| Andrea Fioraldi <andreafioraldi@gmail.com> |
| |
| Copyright 2016, 2017 Google Inc. All rights reserved. |
| Copyright 2019-2020 AFLplusplus Project. 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 |
| |
| Shared code that implements a forkserver. This is used by the fuzzer |
| as well the other components like afl-tmin. |
| |
| */ |
| |
| #include "config.h" |
| #include "types.h" |
| #include "debug.h" |
| #include "common.h" |
| #include "list.h" |
| #include "forkserver.h" |
| |
| #include <stdio.h> |
| #include <unistd.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <time.h> |
| #include <errno.h> |
| #include <signal.h> |
| #include <sys/time.h> |
| #include <sys/wait.h> |
| #include <sys/resource.h> |
| #include <sys/select.h> |
| |
| /** |
| * The correct fds for reading and writing pipes |
| */ |
| |
| /* Describe integer as memory size. */ |
| |
| list_t fsrv_list = {.element_prealloc_count = 0}; |
| |
| /* Initializes the struct */ |
| |
| void afl_fsrv_init(afl_forkserver_t *fsrv) { |
| |
| // this structure needs default so we initialize it if this was not done |
| // already |
| |
| fsrv->use_stdin = 1; |
| fsrv->out_fd = -1; |
| fsrv->out_dir_fd = -1; |
| fsrv->dev_null_fd = -1; |
| #ifndef HAVE_ARC4RANDOM |
| fsrv->dev_urandom_fd = -1; |
| #endif |
| fsrv->exec_tmout = EXEC_TIMEOUT; |
| fsrv->mem_limit = MEM_LIMIT; |
| fsrv->child_pid = -1; |
| fsrv->out_dir_fd = -1; |
| |
| fsrv->use_fauxsrv = 0; |
| fsrv->prev_timed_out = 0; |
| |
| list_append(&fsrv_list, fsrv); |
| |
| } |
| |
| /* Internal forkserver for dumb_mode=1 and non-forkserver mode runs. |
| It execvs for each fork, forwarding exit codes and child pids to afl. */ |
| |
| static void afl_fauxsrv_execv(afl_forkserver_t *fsrv, char **argv) { |
| |
| unsigned char tmp[4] = {0}; |
| pid_t child_pid = -1; |
| |
| /* Phone home and tell the parent that we're OK. If parent isn't there, |
| assume we're not running in forkserver mode and just execute program. */ |
| |
| if (write(FORKSRV_FD + 1, tmp, 4) != 4) abort(); // TODO: Abort? |
| |
| void (*old_sigchld_handler)(int) = signal(SIGCHLD, SIG_DFL); |
| |
| while (1) { |
| |
| uint32_t was_killed; |
| int status; |
| |
| /* Wait for parent by reading from the pipe. Exit if read fails. */ |
| |
| if (read(FORKSRV_FD, &was_killed, 4) != 4) exit(0); |
| |
| /* Create a clone of our process. */ |
| |
| child_pid = fork(); |
| |
| if (child_pid < 0) PFATAL("Fork failed"); |
| |
| /* In child process: close fds, resume execution. */ |
| |
| if (!child_pid) { // New child |
| |
| signal(SIGCHLD, old_sigchld_handler); |
| // FORKSRV_FD is for communication with AFL, we don't need it in the |
| // child. |
| close(FORKSRV_FD); |
| close(FORKSRV_FD + 1); |
| |
| // TODO: exec... |
| |
| execv(fsrv->target_path, argv); |
| |
| /* Use a distinctive bitmap signature to tell the parent about execv() |
| falling through. */ |
| |
| *(u32 *)fsrv->trace_bits = EXEC_FAIL_SIG; |
| |
| PFATAL("Execv failed in fauxserver."); |
| |
| } |
| |
| /* In parent process: write PID to AFL. */ |
| |
| if (write(FORKSRV_FD + 1, &child_pid, 4) != 4) exit(0); |
| |
| /* after child exited, get and relay exit status to parent through waitpid. |
| */ |
| |
| if (waitpid(child_pid, &status, 0) < 0) { |
| |
| // Zombie Child could not be collected. Scary! |
| PFATAL("Fauxserver could not determin child's exit code. "); |
| |
| } |
| |
| /* Relay wait status to AFL pipe, then loop back. */ |
| |
| if (write(FORKSRV_FD + 1, &status, 4) != 4) exit(0); |
| |
| } |
| |
| } |
| |
| /* Spins up fork server (instrumented mode only). The idea is explained here: |
| |
| http://lcamtuf.blogspot.com/2014/10/fuzzing-binaries-without-execve.html |
| |
| In essence, the instrumentation allows us to skip execve(), and just keep |
| cloning a stopped child. So, we just execute once, and then send commands |
| through a pipe. The other part of this logic is in afl-as.h / llvm_mode */ |
| |
| void afl_fsrv_start(afl_forkserver_t *fsrv, char **argv) { |
| |
| int st_pipe[2], ctl_pipe[2]; |
| int status; |
| s32 rlen; |
| |
| if (fsrv->use_fauxsrv) ACTF("Using Fauxserver:"); |
| |
| if (!getenv("AFL_QUIET")) ACTF("Spinning up the fork server..."); |
| |
| if (pipe(st_pipe) || pipe(ctl_pipe)) PFATAL("pipe() failed"); |
| |
| fsrv->child_timed_out = 0; |
| fsrv->fsrv_pid = fork(); |
| |
| if (fsrv->fsrv_pid < 0) PFATAL("fork() failed"); |
| |
| if (!fsrv->fsrv_pid) { |
| |
| /* CHILD PROCESS */ |
| |
| struct rlimit r; |
| |
| /* Umpf. On OpenBSD, the default fd limit for root users is set to |
| soft 128. Let's try to fix that... */ |
| |
| if (!getrlimit(RLIMIT_NOFILE, &r) && r.rlim_cur < FORKSRV_FD + 2) { |
| |
| r.rlim_cur = FORKSRV_FD + 2; |
| setrlimit(RLIMIT_NOFILE, &r); /* Ignore errors */ |
| |
| } |
| |
| if (fsrv->mem_limit) { |
| |
| r.rlim_max = r.rlim_cur = ((rlim_t)fsrv->mem_limit) << 20; |
| |
| #ifdef RLIMIT_AS |
| setrlimit(RLIMIT_AS, &r); /* Ignore errors */ |
| #else |
| /* This takes care of OpenBSD, which doesn't have RLIMIT_AS, but |
| according to reliable sources, RLIMIT_DATA covers anonymous |
| maps - so we should be getting good protection against OOM bugs. */ |
| |
| setrlimit(RLIMIT_DATA, &r); /* Ignore errors */ |
| #endif /* ^RLIMIT_AS */ |
| |
| } |
| |
| /* Dumping cores is slow and can lead to anomalies if SIGKILL is delivered |
| before the dump is complete. */ |
| |
| // r.rlim_max = r.rlim_cur = 0; |
| // setrlimit(RLIMIT_CORE, &r); /* Ignore errors */ |
| |
| /* Isolate the process and configure standard descriptors. If out_file is |
| specified, stdin is /dev/null; otherwise, out_fd is cloned instead. */ |
| |
| setsid(); |
| |
| if (!get_afl_env("AFL_DEBUG_CHILD_OUTPUT")) { |
| |
| dup2(fsrv->dev_null_fd, 1); |
| dup2(fsrv->dev_null_fd, 2); |
| |
| } |
| |
| if (!fsrv->use_stdin) { |
| |
| dup2(fsrv->dev_null_fd, 0); |
| |
| } else { |
| |
| dup2(fsrv->out_fd, 0); |
| close(fsrv->out_fd); |
| |
| } |
| |
| /* Set up control and status pipes, close the unneeded original fds. */ |
| |
| if (dup2(ctl_pipe[0], FORKSRV_FD) < 0) PFATAL("dup2() failed"); |
| if (dup2(st_pipe[1], FORKSRV_FD + 1) < 0) PFATAL("dup2() failed"); |
| |
| close(ctl_pipe[0]); |
| close(ctl_pipe[1]); |
| close(st_pipe[0]); |
| close(st_pipe[1]); |
| |
| close(fsrv->out_dir_fd); |
| close(fsrv->dev_null_fd); |
| #ifndef HAVE_ARC4RANDOM |
| close(fsrv->dev_urandom_fd); |
| #endif |
| close(fsrv->plot_file == NULL ? -1 : fileno(fsrv->plot_file)); |
| |
| /* This should improve performance a bit, since it stops the linker from |
| doing extra work post-fork(). */ |
| |
| if (!getenv("LD_BIND_LAZY")) setenv("LD_BIND_NOW", "1", 0); |
| |
| /* Set sane defaults for ASAN if nothing else specified. */ |
| |
| setenv("ASAN_OPTIONS", |
| "abort_on_error=1:" |
| "detect_leaks=0:" |
| "malloc_context_size=0:" |
| "symbolize=0:" |
| "allocator_may_return_null=1", |
| 0); |
| |
| /* MSAN is tricky, because it doesn't support abort_on_error=1 at this |
| point. So, we do this in a very hacky way. */ |
| |
| setenv("MSAN_OPTIONS", |
| "exit_code=" STRINGIFY(MSAN_ERROR) ":" |
| "symbolize=0:" |
| "abort_on_error=1:" |
| "malloc_context_size=0:" |
| "allocator_may_return_null=1:" |
| "msan_track_origins=0", |
| 0); |
| |
| if (fsrv->use_fauxsrv) { |
| |
| afl_fauxsrv_execv(fsrv, argv); |
| |
| } else { |
| |
| execv(fsrv->target_path, argv); |
| |
| } |
| |
| /* Use a distinctive bitmap signature to tell the parent about execv() |
| falling through. */ |
| |
| *(u32 *)fsrv->trace_bits = EXEC_FAIL_SIG; |
| exit(0); |
| |
| } |
| |
| /* PARENT PROCESS */ |
| |
| /* Close the unneeded endpoints. */ |
| |
| close(ctl_pipe[0]); |
| close(st_pipe[1]); |
| |
| fsrv->fsrv_ctl_fd = ctl_pipe[1]; |
| fsrv->fsrv_st_fd = st_pipe[0]; |
| |
| /* Wait for the fork server to come up, but don't wait too long. */ |
| |
| rlen = 0; |
| if (fsrv->exec_tmout) { |
| |
| rlen = 4; |
| u32 time = read_timed(fsrv->fsrv_st_fd, &status, rlen, |
| fsrv->exec_tmout * FORK_WAIT_MULT); |
| |
| if (time > fsrv->exec_tmout * FORK_WAIT_MULT) { |
| |
| fsrv->child_timed_out = 1; |
| kill(fsrv->fsrv_pid, SIGKILL); |
| |
| } |
| |
| if (!time) { kill(fsrv->fsrv_pid, SIGKILL); } |
| |
| } else { |
| |
| rlen = read(fsrv->fsrv_st_fd, &status, 4); |
| |
| } |
| |
| /* If we have a four-byte "hello" message from the server, we're all set. |
| Otherwise, try to figure out what went wrong. */ |
| |
| if (rlen == 4) { |
| |
| if (!getenv("AFL_QUIET")) OKF("All right - fork server is up."); |
| return; |
| |
| } |
| |
| if (fsrv->child_timed_out) |
| FATAL("Timeout while initializing fork server (adjusting -t may help)"); |
| |
| if (waitpid(fsrv->fsrv_pid, &status, 0) <= 0) PFATAL("waitpid() failed"); |
| |
| if (WIFSIGNALED(status)) { |
| |
| if (fsrv->mem_limit && fsrv->mem_limit < 500 && fsrv->uses_asan) { |
| |
| SAYF("\n" cLRD "[-] " cRST |
| "Whoops, the target binary crashed suddenly, " |
| "before receiving any input\n" |
| " from the fuzzer! Since it seems to be built with ASAN and you " |
| "have a\n" |
| " restrictive memory limit configured, this is expected; please " |
| "read\n" |
| " %s/notes_for_asan.md for help.\n", |
| doc_path); |
| |
| } else if (!fsrv->mem_limit) { |
| |
| SAYF("\n" cLRD "[-] " cRST |
| "Whoops, the target binary crashed suddenly, " |
| "before receiving any input\n" |
| " from the fuzzer! There are several probable explanations:\n\n" |
| |
| " - The binary is just buggy and explodes entirely on its own. " |
| "If so, you\n" |
| " need to fix the underlying problem or find a better " |
| "replacement.\n\n" |
| |
| MSG_FORK_ON_APPLE |
| |
| " - Less likely, there is a horrible bug in the fuzzer. If other " |
| "options\n" |
| " fail, poke <afl-users@googlegroups.com> for troubleshooting " |
| "tips.\n"); |
| |
| } else { |
| |
| u8 val_buf[STRINGIFY_VAL_SIZE_MAX]; |
| |
| SAYF("\n" cLRD "[-] " cRST |
| "Whoops, the target binary crashed suddenly, " |
| "before receiving any input\n" |
| " from the fuzzer! There are several probable explanations:\n\n" |
| |
| " - The current memory limit (%s) is too restrictive, causing " |
| "the\n" |
| " target to hit an OOM condition in the dynamic linker. Try " |
| "bumping up\n" |
| " the limit with the -m setting in the command line. A simple " |
| "way confirm\n" |
| " this diagnosis would be:\n\n" |
| |
| MSG_ULIMIT_USAGE |
| " /path/to/fuzzed_app )\n\n" |
| |
| " Tip: you can use http://jwilk.net/software/recidivm to " |
| "quickly\n" |
| " estimate the required amount of virtual memory for the " |
| "binary.\n\n" |
| |
| " - The binary is just buggy and explodes entirely on its own. " |
| "If so, you\n" |
| " need to fix the underlying problem or find a better " |
| "replacement.\n\n" |
| |
| MSG_FORK_ON_APPLE |
| |
| " - Less likely, there is a horrible bug in the fuzzer. If other " |
| "options\n" |
| " fail, poke <afl-users@googlegroups.com> for troubleshooting " |
| "tips.\n", |
| stringify_mem_size(val_buf, sizeof(val_buf), fsrv->mem_limit << 20), |
| fsrv->mem_limit - 1); |
| |
| } |
| |
| FATAL("Fork server crashed with signal %d", WTERMSIG(status)); |
| |
| } |
| |
| if (*(u32 *)fsrv->trace_bits == EXEC_FAIL_SIG) |
| FATAL("Unable to execute target application ('%s')", argv[0]); |
| |
| if (fsrv->mem_limit && fsrv->mem_limit < 500 && fsrv->uses_asan) { |
| |
| SAYF("\n" cLRD "[-] " cRST |
| "Hmm, looks like the target binary terminated " |
| "before we could complete a\n" |
| " handshake with the injected code. Since it seems to be built " |
| "with ASAN and\n" |
| " you have a restrictive memory limit configured, this is " |
| "expected; please\n" |
| " read %s/notes_for_asan.md for help.\n", |
| doc_path); |
| |
| } else if (!fsrv->mem_limit) { |
| |
| SAYF("\n" cLRD "[-] " cRST |
| "Hmm, looks like the target binary terminated " |
| "before we could complete a\n" |
| " handshake with the injected code. Perhaps there is a horrible " |
| "bug in the\n" |
| " fuzzer. Poke <afl-users@googlegroups.com> for troubleshooting " |
| "tips.\n"); |
| |
| } else { |
| |
| u8 val_buf[STRINGIFY_VAL_SIZE_MAX]; |
| |
| SAYF( |
| "\n" cLRD "[-] " cRST |
| "Hmm, looks like the target binary terminated " |
| "before we could complete a\n" |
| " handshake with the injected code. There are %s probable " |
| "explanations:\n\n" |
| |
| "%s" |
| " - The current memory limit (%s) is too restrictive, causing an " |
| "OOM\n" |
| " fault in the dynamic linker. This can be fixed with the -m " |
| "option. A\n" |
| " simple way to confirm the diagnosis may be:\n\n" |
| |
| MSG_ULIMIT_USAGE |
| " /path/to/fuzzed_app )\n\n" |
| |
| " Tip: you can use http://jwilk.net/software/recidivm to quickly\n" |
| " estimate the required amount of virtual memory for the " |
| "binary.\n\n" |
| |
| " - Less likely, there is a horrible bug in the fuzzer. If other " |
| "options\n" |
| " fail, poke <afl-users@googlegroups.com> for troubleshooting " |
| "tips.\n", |
| getenv(DEFER_ENV_VAR) ? "three" : "two", |
| getenv(DEFER_ENV_VAR) |
| ? " - You are using deferred forkserver, but __AFL_INIT() is " |
| "never\n" |
| " reached before the program terminates.\n\n" |
| : "", |
| stringify_int(val_buf, sizeof(val_buf), fsrv->mem_limit << 20), |
| fsrv->mem_limit - 1); |
| |
| } |
| |
| FATAL("Fork server handshake failed"); |
| |
| } |
| |
| void afl_fsrv_killall() { |
| |
| LIST_FOREACH(&fsrv_list, afl_forkserver_t, { |
| |
| if (el->child_pid > 0) kill(el->child_pid, SIGKILL); |
| |
| }); |
| |
| } |
| |
| void afl_fsrv_deinit(afl_forkserver_t *fsrv) { |
| |
| list_remove(&fsrv_list, fsrv); |
| |
| } |
| |
