/* american fuzzy lop++ - forkserver code -------------------------------------- Originally written by Michal Zalewski Forkserver design by Jann Horn Now maintained by by Marc Heuse , Heiko Eißfeldt and Andrea Fioraldi Copyright 2016, 2017 Google Inc. All rights reserved. Copyright 2019 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 "forkserver.h" #include #include #include #include #include #include #include #include #include #include /* a program that includes afl-forkserver needs to define these */ extern u8 uses_asan; extern u8 *trace_bits; extern s32 forksrv_pid, child_pid, fsrv_ctl_fd, fsrv_st_fd; extern s32 out_fd, out_dir_fd, dev_null_fd; /* initialize these with -1 */ #ifndef HAVE_ARC4RANDOM extern s32 dev_urandom_fd; #endif extern u32 exec_tmout; extern u64 mem_limit; extern u8 * out_file, *target_path, *doc_path; extern FILE *plot_file; /* we need this internally but can be defined and read extern in the main source */ u8 child_timed_out; /* Describe integer as memory size. */ u8 *forkserver_DMS(u64 val) { static u8 tmp[12][16]; static u8 cur; #define CHK_FORMAT(_divisor, _limit_mult, _fmt, _cast) \ do { \ \ if (val < (_divisor) * (_limit_mult)) { \ \ sprintf(tmp[cur], _fmt, ((_cast)val) / (_divisor)); \ return tmp[cur]; \ \ } \ \ } while (0) cur = (cur + 1) % 12; /* 0-9999 */ CHK_FORMAT(1, 10000, "%llu B", u64); /* 10.0k - 99.9k */ CHK_FORMAT(1024, 99.95, "%0.01f kB", double); /* 100k - 999k */ CHK_FORMAT(1024, 1000, "%llu kB", u64); /* 1.00M - 9.99M */ CHK_FORMAT(1024 * 1024, 9.995, "%0.02f MB", double); /* 10.0M - 99.9M */ CHK_FORMAT(1024 * 1024, 99.95, "%0.01f MB", double); /* 100M - 999M */ CHK_FORMAT(1024 * 1024, 1000, "%llu MB", u64); /* 1.00G - 9.99G */ CHK_FORMAT(1024LL * 1024 * 1024, 9.995, "%0.02f GB", double); /* 10.0G - 99.9G */ CHK_FORMAT(1024LL * 1024 * 1024, 99.95, "%0.01f GB", double); /* 100G - 999G */ CHK_FORMAT(1024LL * 1024 * 1024, 1000, "%llu GB", u64); /* 1.00T - 9.99G */ CHK_FORMAT(1024LL * 1024 * 1024 * 1024, 9.995, "%0.02f TB", double); /* 10.0T - 99.9T */ CHK_FORMAT(1024LL * 1024 * 1024 * 1024, 99.95, "%0.01f TB", double); #undef CHK_FORMAT /* 100T+ */ strcpy(tmp[cur], "infty"); return tmp[cur]; } /* the timeout handler */ void handle_timeout(int sig) { if (child_pid > 0) { child_timed_out = 1; kill(child_pid, SIGKILL); } else if (child_pid == -1 && forksrv_pid > 0) { child_timed_out = 1; kill(forksrv_pid, SIGKILL); } } /* Spin 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 init_forkserver(char **argv) { static struct itimerval it; int st_pipe[2], ctl_pipe[2]; int status; s32 rlen; ACTF("Spinning up the fork server..."); if (pipe(st_pipe) || pipe(ctl_pipe)) PFATAL("pipe() failed"); child_timed_out = 0; forksrv_pid = fork(); if (forksrv_pid < 0) PFATAL("fork() failed"); if (!forksrv_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 (mem_limit) { r.rlim_max = r.rlim_cur = ((rlim_t)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 (!getenv("AFL_DEBUG_CHILD_OUTPUT")) { dup2(dev_null_fd, 1); dup2(dev_null_fd, 2); } if (out_file) { dup2(dev_null_fd, 0); } else { dup2(out_fd, 0); close(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(out_dir_fd); close(dev_null_fd); #ifndef HAVE_ARC4RANDOM close(dev_urandom_fd); #endif close(plot_file == NULL ? -1 : fileno(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); execv(target_path, argv); /* Use a distinctive bitmap signature to tell the parent about execv() falling through. */ *(u32 *)trace_bits = EXEC_FAIL_SIG; exit(0); } /* PARENT PROCESS */ /* Close the unneeded endpoints. */ close(ctl_pipe[0]); close(st_pipe[1]); fsrv_ctl_fd = ctl_pipe[1]; fsrv_st_fd = st_pipe[0]; /* Wait for the fork server to come up, but don't wait too long. */ if (exec_tmout) { it.it_value.tv_sec = ((exec_tmout * FORK_WAIT_MULT) / 1000); it.it_value.tv_usec = ((exec_tmout * FORK_WAIT_MULT) % 1000) * 1000; } setitimer(ITIMER_REAL, &it, NULL); rlen = read(fsrv_st_fd, &status, 4); it.it_value.tv_sec = 0; it.it_value.tv_usec = 0; setitimer(ITIMER_REAL, &it, NULL); /* 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) { OKF("All right - fork server is up."); return; } if (child_timed_out) FATAL("Timeout while initializing fork server (adjusting -t may help)"); if (waitpid(forksrv_pid, &status, 0) <= 0) PFATAL("waitpid() failed"); if (WIFSIGNALED(status)) { if (mem_limit && mem_limit < 500 && 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.txt for help.\n", doc_path); } else if (!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 for troubleshooting " "tips.\n"); } else { 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 for troubleshooting " "tips.\n", forkserver_DMS(mem_limit << 20), mem_limit - 1); } FATAL("Fork server crashed with signal %d", WTERMSIG(status)); } if (*(u32 *)trace_bits == EXEC_FAIL_SIG) FATAL("Unable to execute target application ('%s')", argv[0]); if (mem_limit && mem_limit < 500 && 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.txt for help.\n", doc_path); } else if (!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 for troubleshooting " "tips.\n"); } else { 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 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" : "", forkserver_DMS(mem_limit << 20), mem_limit - 1); } FATAL("Fork server handshake failed"); }