fauxserver

Makefile

@@ -146,7 +146,7 @@ ifdef STATIC
   PYFLAGS=
 
   CFLAGS += -static
-  LDFLAGS += -lm -lrt -lpthread -lz -lutil
+  LDFLAGS += -lm -lpthread -lz -lutil
 endif
 
 ifeq "$(shell echo '$(HASH)include <sys/ipc.h>@$(HASH)include <sys/shm.h>@int main() { int _id = shmget(IPC_PRIVATE, 65536, IPC_CREAT | IPC_EXCL | 0600); shmctl(_id, IPC_RMID, 0); return 0;}' | tr @ '\n' | $(CC) -x c - -o .test2 2>/dev/null && echo 1 || echo 0 ; rm -f .test2 )" "1"
@@ -154,13 +154,13 @@ ifeq "$(shell echo '$(HASH)include <sys/ipc.h>@$(HASH)include <sys/shm.h>@int ma
 else
 	SHMAT_OK=0
 	CFLAGS+=-DUSEMMAP=1
-	LDFLAGS+=-Wno-deprecated-declarations -lrt
+	LDFLAGS+=-Wno-deprecated-declarations
 endif
 
 ifeq "$(TEST_MMAP)" "1"
 	SHMAT_OK=0
 	CFLAGS+=-DUSEMMAP=1
-	LDFLAGS+=-Wno-deprecated-declarations -lrt
+	LDFLAGS+=-Wno-deprecated-declarations
 endif
 
 ifdef ASAN_BUILD
@@ -282,7 +282,7 @@ src/third_party/libradamsa/libradamsa.so: src/third_party/libradamsa/libradamsa.
 	$(MAKE) -C src/third_party/libradamsa/ CFLAGS="$(CFLAGS)"
 
 afl-fuzz: $(COMM_HDR) include/afl-fuzz.h $(AFL_FUZZ_FILES) src/afl-common.o src/afl-sharedmem.o src/afl-forkserver.o | test_x86
-	$(CC) $(CFLAGS) $(CFLAGS_FLTO) $(AFL_FUZZ_FILES) -lrt src/afl-common.o src/afl-sharedmem.o src/afl-forkserver.o -o $@ $(PYFLAGS) $(LDFLAGS)
+	$(CC) $(CFLAGS) $(CFLAGS_FLTO) $(AFL_FUZZ_FILES) src/afl-common.o src/afl-sharedmem.o src/afl-forkserver.o -o $@ $(PYFLAGS) $(LDFLAGS)
 
 afl-showmap: src/afl-showmap.c src/afl-common.o src/afl-sharedmem.o $(COMM_HDR) | test_x86
 	$(CC) $(CFLAGS) $(CFLAGS_FLTO) src/$@.c src/afl-common.o src/afl-sharedmem.o src/afl-forkserver.o -o $@ $(LDFLAGS)

include/forkserver.h

@@ -42,7 +42,7 @@ typedef struct afl_forkserver {
       child_pid,                        /* PID of the fuzzed program        */
       out_dir_fd;                       /* FD of the lock file              */
 
-  s32 out_fd,                 /* Persistent fd for afl->fsrv.out_file       */
+  s32 out_fd,                           /* Persistent fd for fsrv->out_file */
 #ifndef HAVE_ARC4RANDOM
       dev_urandom_fd,                   /* Persistent fd for /dev/urandom   */
 #endif
@@ -60,6 +60,8 @@ typedef struct afl_forkserver {
 
   u8 child_timed_out;                   /* Traced process timed out?        */
 
+  u8 use_fauxsrv;                       /* Fauxsrv for non-forking targets? */
+
 } afl_forkserver_t;
 
 void handle_timeout(int sig);

src/afl-common.c

@@ -43,14 +43,11 @@ void detect_file_args(char **argv, u8 *prog_in, u8 *use_stdin) {
 
   u32 i = 0;
   u8  cwd[PATH_MAX];
-  if (getcwd(cwd, (size_t)sizeof(cwd)) == NULL) {
+  if (getcwd(cwd, (size_t)sizeof(cwd)) == NULL) { PFATAL("getcwd() failed"); }
-
-    PFATAL("getcwd() failed");
-
-  }
 
   /* we are working with libc-heap-allocated argvs. So do not mix them with
-   * other allocation APIs like ck_alloc. That would disturb the free() calls. */
+   * other allocation APIs like ck_alloc. That would disturb the free() calls.
+   */
   while (argv[i]) {
 
     u8 *aa_loc = strstr(argv[i], "@@");
@@ -72,10 +69,15 @@ void detect_file_args(char **argv, u8 *prog_in, u8 *use_stdin) {
         /* Construct a replacement argv value. */
 
         if (prog_in[0] == '/') {
+
           n_arg = alloc_printf("%s%s%s", argv[i], prog_in, aa_loc + 2);
+
         } else {
+
           n_arg = alloc_printf("%s%s/%s%s", argv[i], cwd, prog_in, aa_loc + 2);
+
         }
+
         ck_free(argv[i]);
         argv[i] = n_arg;
 
@@ -86,7 +88,9 @@ void detect_file_args(char **argv, u8 *prog_in, u8 *use_stdin) {
     i++;
 
   }
+
   /* argvs are automatically freed at exit. */
+
 }
 
 /* duplicate the system argv so that

src/afl-forkserver.c

@@ -43,6 +43,10 @@
 #include <sys/resource.h>
 #include <sys/select.h>
 
+/**
+ * The correct fds for reading and writing pipes
+ */
+
 /* Describe integer as memory size. */
 
 extern u8 *doc_path;
@@ -151,10 +155,87 @@ void afl_fsrv_init(afl_forkserver_t *fsrv) {
   fsrv->child_pid = -1;
   fsrv->out_dir_fd = -1;
 
+  fsrv->use_fauxsrv = 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) {
+
+  static 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
@@ -170,6 +251,8 @@ void afl_fsrv_start(afl_forkserver_t *fsrv, char **argv) {
   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");
@@ -284,8 +367,16 @@ void afl_fsrv_start(afl_forkserver_t *fsrv, char **argv) {
            "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. */
 

src/afl-fuzz-run.c

@@ -39,16 +39,16 @@ void timeout_handle(union sigval timer_data) {
 
 u8 run_target(afl_state_t *afl, u32 timeout) {
 
-  struct sigevent          timer_signal_event;
+  s32 res;
-  static timer_t           timer;
+  int sret;
-  static struct itimerspec timer_period;
+
+  fd_set readfds;
+
   static struct timeval it;
   static u32            prev_timed_out = 0;
-  static u64               exec_ms = 0;
 
   int status = 0;
   u32 tb4;
-  int timer_status;
 
   afl->fsrv.child_timed_out = 0;
 
@@ -57,138 +57,12 @@ u8 run_target(afl_state_t *afl, u32 timeout) {
      territory. */
 
   memset(afl->fsrv.trace_bits, 0, MAP_SIZE);
-  memset(&timer_signal_event, 0, sizeof(struct sigevent));
-
-  timer_signal_event.sigev_notify = SIGEV_THREAD;
-  timer_signal_event.sigev_notify_function = timeout_handle;
 
   MEM_BARRIER();
 
-  /* If we're running in "dumb" mode, we can't rely on the fork server
+  /* we have the fork server (or faux server) up and running, so simply
-     logic compiled into the target program, so we will just keep calling
-     execve(). There is a bit of code duplication between here and
-     init_forkserver(), but c'est la vie. */
-
-  if (afl->dumb_mode == 1 || afl->no_forkserver) {
-
-    afl->fsrv.child_pid = fork();
-
-    if (afl->fsrv.child_pid < 0) PFATAL("fork() failed");
-
-    if (!afl->fsrv.child_pid) {
-
-      struct rlimit r;
-
-      if (afl->fsrv.mem_limit) {
-
-        r.rlim_max = r.rlim_cur = ((rlim_t)afl->fsrv.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 */
-
-      /* Isolate the process and configure standard descriptors. If
-         afl->fsrv.out_file is specified, stdin is /dev/null; otherwise,
-         afl->fsrv.out_fd is cloned instead. */
-
-      setsid();
-
-      dup2(afl->fsrv.dev_null_fd, 1);
-      dup2(afl->fsrv.dev_null_fd, 2);
-
-      if (afl->fsrv.out_file) {
-
-        dup2(afl->fsrv.dev_null_fd, 0);
-
-      } else {
-
-        dup2(afl->fsrv.out_fd, 0);
-        close(afl->fsrv.out_fd);
-
-      }
-
-      /* On Linux, would be faster to use O_CLOEXEC. Maybe TODO. */
-
-      close(afl->fsrv.dev_null_fd);
-      close(afl->fsrv.out_dir_fd);
-#ifndef HAVE_ARC4RANDOM
-      close(afl->fsrv.dev_urandom_fd);
-#endif
-      close(fileno(afl->fsrv.plot_file));
-
-      /* Set sane defaults for ASAN if nothing else specified. */
-
-      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:"
-                             "msan_track_origins=0", 0);
-
-      execv(afl->fsrv.target_path, afl->argv);
-
-      /* Use a distinctive bitmap value to tell the parent about execv()
-         falling through. */
-
-      *(u32 *)afl->fsrv.trace_bits = EXEC_FAIL_SIG;
-      exit(0);
-
-    }
-
-    /* Configure timeout using POSIX timers in dumb-mode,
-        as requested by user, then wait for child to terminate.
-     */
-
-    timer_signal_event.sigev_value.sival_int = afl->fsrv.child_pid;
-    timer_status = timer_create(CLOCK_MONOTONIC, &timer_signal_event, &timer);
-
-    if (timer_status == -1) { FATAL("Failed to create Timer"); }
-
-    timer_period.it_value.tv_sec = (timeout / 1000);
-    timer_period.it_value.tv_nsec = (timeout % 1000) * 1000000;
-    timer_period.it_interval.tv_sec = 0;
-    timer_period.it_interval.tv_nsec = 0;
-
-    timer_status = timer_settime(timer, 0, &timer_period, NULL);
-
-    if (timer_status == -1) {
-
-      timer_delete(timer);
-      if (errno == EINVAL) {
-
-        FATAL("Failed to set the timer. The timeout given is invalid.");
-
-      } else {
-
-        FATAL("Failed to set the timer to the given timeout");
-
-      }
-
-    }
-
-  } else {
-
-    /* In non-dumb mode, we have the fork server up and running, so simply
       tell it to have at it, and then read back PID. */
 
-    int res;
-
   if ((res = write(afl->fsrv.fsrv_ctl_fd, &prev_timed_out, 4)) != 4) {
 
     if (afl->stop_soon) return 0;
@@ -205,43 +79,8 @@ u8 run_target(afl_state_t *afl, u32 timeout) {
 
   if (afl->fsrv.child_pid <= 0) FATAL("Fork server is misbehaving (OOM?)");
 
-  }
+  /* use select to monitor the forkserver for timeouts. */
 
-  if (afl->dumb_mode == 1 || afl->no_forkserver) {
-
-    if (waitpid(afl->fsrv.child_pid, &status, 0) <= 0) {
-
-      timer_delete(timer);
-      PFATAL("waitpid() failed");
-
-    }
-
-    timer_gettime(timer, &timer_period);
-    exec_ms = (u64)timeout - (timer_period.it_value.tv_sec * 1000 +
-                              timer_period.it_value.tv_nsec / 1000000);
-    timer_period.it_value.tv_sec = 0;
-    timer_period.it_value.tv_nsec = 0;
-
-    timer_status = timer_settime(timer, 0, &timer_period, NULL);
-
-    if (timer_status == -1) {
-
-      timer_delete(timer);
-      FATAL("Failed to reset the timer.");
-
-    }
-
-    timer_delete(timer);
-
-  } else {
-
-    /* In non-dumb mode, use select to monitor the forkserver for timeouts.
-     */
-
-    s32 res;
-    int sret;
-
-    fd_set readfds;
   FD_ZERO(&readfds);
   FD_SET(afl->fsrv.fsrv_st_fd, &readfds);
   it.tv_sec = ((timeout) / 1000);
@@ -251,15 +90,18 @@ u8 run_target(afl_state_t *afl, u32 timeout) {
 
   if (sret == 0) {
 
-      kill(afl->fsrv.child_pid, SIGKILL);
+    /* If there was no response from forkserver after timeout seconds,
+    we kill the child. The forkserver should inform us afterwards */
 
-    } else {
+    kill(afl->fsrv.child_pid, SIGKILL);
+    afl->fsrv.child_timed_out = 1;
+
+  }
 
   if ((res = read(afl->fsrv.fsrv_st_fd, &status, 4)) != 4) {
 
     if (afl->stop_soon) return 0;
-        SAYF(
+    SAYF("\n" cLRD "[-] " cRST
-            "\n" cLRD "[-] " cRST
          "Unable to communicate with fork server. Some possible reasons:\n\n"
          "    - You've run out of memory. Use -m to increase the the memory "
          "limit\n"
@@ -284,18 +126,8 @@ u8 run_target(afl_state_t *afl, u32 timeout) {
 
   }
 
-    }
-
-    exec_ms = (u64)timeout - (it.tv_sec * 1000 + it.tv_usec / 1000);
-    it.tv_sec = 0;
-    it.tv_usec = 0;
-
-  }
-
   if (!WIFSTOPPED(status)) afl->fsrv.child_pid = 0;
 
-  if (exec_ms >= timeout) { afl->fsrv.child_timed_out = 1; }
-
   ++afl->total_execs;
 
   /* Any subsequent operations on afl->fsrv.trace_bits must not be moved by the
@@ -494,8 +326,7 @@ u8 calibrate_case(afl_state_t *afl, struct queue_entry *q, u8 *use_mem,
   /* Make sure the forkserver is up before we do anything, and let's not
      count its spin-up time toward binary calibration. */
 
-  if (afl->dumb_mode != 1 && !afl->no_forkserver && !afl->fsrv.fsrv_pid)
+  if (!afl->fsrv.fsrv_pid) afl_fsrv_start(&afl->fsrv, afl->argv);
-    afl_fsrv_start(&afl->fsrv, afl->argv);
   if (afl->dumb_mode != 1 && !afl->no_forkserver && !afl->cmplog_fsrv_pid &&
       afl->shm.cmplog_mode)
     init_cmplog_forkserver(afl);

src/afl-fuzz.c

@@ -785,6 +785,8 @@ int main(int argc, char **argv_orig, char **envp) {
   if (afl->dumb_mode == 2 && afl->no_forkserver)
     FATAL("AFL_DUMB_FORKSRV and AFL_NO_FORKSRV are mutually exclusive");
 
+  afl->fsrv.use_fauxsrv = afl->dumb_mode == 1 || afl->no_forkserver;
+
   if (getenv("LD_PRELOAD"))
     WARNF(
         "LD_PRELOAD is set, are you sure that is what to you want to do "