Add AFL_FORK_SERVER_KILL_SIGNAL environment variable.

The AFL_FORK_SERVER_KILL_SIGNAL variable allows to configure the signal
used to kill the fork server on termination.

afl-cmin

@@ -123,6 +123,8 @@ function usage() {
 "AFL_FORKSRV_INIT_TMOUT: time the fuzzer waits for the forkserver to come up\n" \
 "AFL_KEEP_TRACES: leave the temporary <out_dir>/.traces directory\n" \
 "AFL_KILL_SIGNAL: Signal delivered to child processes on timeout (default: SIGKILL)\n" \
+"AFL_FORK_SERVER_KILL_SIGNAL: Signal delivered to fork server processes on termination\n"
+"                             (default: SIGTERM)\n"
 "AFL_NO_FORKSRV: run target via execve instead of using the forkserver\n" \
 "AFL_CMIN_ALLOW_ANY: write tuples for crashing inputs also\n" \
 "AFL_PATH: path for the afl-showmap binary if not found anywhere in PATH\n" \

docs/env_variables.md

@@ -409,11 +409,18 @@ checks or alter some of the more exotic semantics of the tool:
     the afl-fuzz -g/-G command line option to control the minimum/maximum
     of fuzzing input generated.
 
-  - `AFL_KILL_SIGNAL`: Set the signal ID to be delivered to child processes on
-    timeout. Unless you implement your own targets or instrumentation, you
+  - `AFL_KILL_SIGNAL`: Set the signal ID to be delivered to child processes
+    on timeout. Unless you implement your own targets or instrumentation, you
     likely don't have to set it. By default, on timeout and on exit, `SIGKILL`
     (`AFL_KILL_SIGNAL=9`) will be delivered to the child.
 
+  - `AFL_FORK_SERVER_KILL_SIGNAL`: Set the signal ID to be delivered to the
+    fork server when AFL++ is terminated. Unless you implement your
+    fork server, you likely do not have to set it. By default, `SIGTERM`
+    (`AFL_FORK_SERVER_KILL_SIGNAL=15`) will be delivered to the fork server.
+    NOTE: Uncatchable signals, such as `SIGKILL`, cause child processes of
+    the fork server to be orphaned and leaves them in a zombie state.
+
   - `AFL_MAP_SIZE` sets the size of the shared map that afl-analyze, afl-fuzz,
     afl-showmap, and afl-tmin create to gather instrumentation data from the
     target. This must be equal or larger than the size the target was compiled

include/afl-fuzz.h

@@ -393,8 +393,8 @@ typedef struct afl_env_vars {
       *afl_hang_tmout, *afl_forksrv_init_tmout, *afl_preload,
       *afl_max_det_extras, *afl_statsd_host, *afl_statsd_port,
       *afl_crash_exitcode, *afl_statsd_tags_flavor, *afl_testcache_size,
-      *afl_testcache_entries, *afl_kill_signal, *afl_target_env,
-      *afl_persistent_record, *afl_exit_on_time;
+      *afl_testcache_entries, *afl_child_kill_signal, *afl_fsrv_kill_signal,
+      *afl_target_env, *afl_persistent_record, *afl_exit_on_time;
 
 } afl_env_vars_t;
 
@@ -1268,4 +1268,3 @@ void queue_testcase_store_mem(afl_state_t *afl, struct queue_entry *q, u8 *mem);
 #endif
 
 #endif
-

include/common.h

@@ -67,10 +67,11 @@ u8 *find_binary(u8 *fname);
 
 u8 *find_afl_binary(u8 *own_loc, u8 *fname);
 
-/* Parses the kill signal environment variable, FATALs on error.
-  If the env is not set, sets the env to default_signal for the signal handlers
-  and returns the default_signal. */
-int parse_afl_kill_signal_env(u8 *afl_kill_signal_env, int default_signal);
+/* Parses the (numeric) kill signal environment variable passed
+   via `numeric_signal_as_str`.
+   If NULL is passed, the `default_signal` value is returned.
+   FATALs if `numeric_signal_as_str` is not a valid integer .*/
+int parse_afl_kill_signal(u8 *numeric_signal_as_str, int default_signal);
 
 /* Read a bitmap from file fname to memory
    This is for the -B option again. */
@@ -133,4 +134,3 @@ FILE *create_ffile(u8 *fn);
 s32 create_file(u8 *fn);
 
 #endif
-

include/envs.h

@@ -110,6 +110,7 @@ static char *afl_environment_variables[] = {
     "AFL_INST_RATIO",
     "AFL_KEEP_TIMEOUTS",
     "AFL_KILL_SIGNAL",
+    "AFL_FORK_SERVER_KILL_SIGNAL",
     "AFL_KEEP_TRACES",
     "AFL_KEEP_ASSEMBLY",
     "AFL_LD_HARD_FAIL",
@@ -239,4 +240,3 @@ static char *afl_environment_variables[] = {
 extern char *afl_environment_variables[];
 
 #endif
-

include/forkserver.h

@@ -164,6 +164,8 @@ typedef struct afl_forkserver {
   void (*add_extra_func)(void *afl_ptr, u8 *mem, u32 len);
 
   u8 child_kill_signal;
+  u8 fsrv_kill_signal;
+
   u8 persistent_mode;
 
 #ifdef __linux__

src/afl-analyze.c

@@ -1116,7 +1116,10 @@ int main(int argc, char **argv_orig, char **envp) {
   }
 
   fsrv.child_kill_signal =
-      parse_afl_kill_signal_env(getenv("AFL_KILL_SIGNAL"), SIGKILL);
+      parse_afl_kill_signal(getenv("AFL_KILL_SIGNAL"), SIGKILL);
+  fsrv.fsrv_kill_signal =
+      parse_afl_kill_signal(getenv("AFL_FORK_SERVER_KILL_SIGNAL"), SIGTERM);
+
 
   read_initial_file();
   (void)check_binary_signatures(fsrv.target_path);

src/afl-common.c

@@ -456,38 +456,24 @@ u8 *find_afl_binary(u8 *own_loc, u8 *fname) {
 
 }
 
-/* Parses the kill signal environment variable, FATALs on error.
-  If the env is not set, sets the env to default_signal for the signal handlers
-  and returns the default_signal. */
-int parse_afl_kill_signal_env(u8 *afl_kill_signal_env, int default_signal) {
 
-  if (afl_kill_signal_env && afl_kill_signal_env[0]) {
+int parse_afl_kill_signal(u8 *numeric_signal_as_str, int default_signal) {
+
+  if (numeric_signal_as_str && numeric_signal_as_str[0]) {
 
     char *endptr;
     u8    signal_code;
-    signal_code = (u8)strtoul(afl_kill_signal_env, &endptr, 10);
+    signal_code = (u8)strtoul(numeric_signal_as_str, &endptr, 10);
     /* Did we manage to parse the full string? */
-    if (*endptr != '\0' || endptr == (char *)afl_kill_signal_env) {
-
-      FATAL("Invalid AFL_KILL_SIGNAL: %s (expected unsigned int)",
-            afl_kill_signal_env);
-
+    if (*endptr != '\0' || endptr == (char *)numeric_signal_as_str) {
+      FATAL("Invalid signal name: %s", numeric_signal_as_str);
+    } else {
+      return signal_code;
     }
 
-    return signal_code;
-
-  } else {
-
-    char *sigstr = alloc_printf("%d", default_signal);
-    if (!sigstr) { FATAL("Failed to alloc mem for signal buf"); }
-
-    /* Set the env for signal handler */
-    setenv("AFL_KILL_SIGNAL", sigstr, 1);
-    free(sigstr);
-    return default_signal;
-
   }
 
+  return default_signal;
 }
 
 static inline unsigned int helper_min3(unsigned int a, unsigned int b,
@@ -1253,4 +1239,3 @@ s32 create_file(u8 *fn) {
   return fd;
 
 }
-

src/afl-forkserver.c

@@ -1245,8 +1245,8 @@ void afl_fsrv_kill(afl_forkserver_t *fsrv) {
   if (fsrv->child_pid > 0) { kill(fsrv->child_pid, fsrv->child_kill_signal); }
   if (fsrv->fsrv_pid > 0) {
 
-    kill(fsrv->fsrv_pid, SIGTERM);
-    if (waitpid(fsrv->fsrv_pid, NULL, 0) <= 0) { WARNF("error waitpid\n"); }
+    kill(fsrv->fsrv_pid, fsrv->fsrv_kill_signal);
+    waitpid(fsrv->fsrv_pid, NULL, 0);
 
   }
 

src/afl-fuzz-state.c

@@ -485,10 +485,15 @@ void read_afl_environment(afl_state_t *afl, char **envp) {
 #endif
 
           } else if (!strncmp(env, "AFL_KILL_SIGNAL",
-
                               afl_environment_variable_len)) {
 
-            afl->afl_env.afl_kill_signal =
+            afl->afl_env.afl_child_kill_signal =
+                (u8 *)get_afl_env(afl_environment_variables[i]);
+
+          } else if (!strncmp(env, "AFL_FORK_SERVER_KILL_SIGNAL",
+                              afl_environment_variable_len)) {
+
+            afl->afl_env.afl_fsrv_kill_signal =
                 (u8 *)get_afl_env(afl_environment_variables[i]);
 
           } else if (!strncmp(env, "AFL_TARGET_ENV",
@@ -657,8 +662,7 @@ void afl_states_stop(void) {
     /* NOTE: We need to make sure that the parent (the forkserver) reap the child (see below). */
     if (el->fsrv.child_pid > 0) kill(el->fsrv.child_pid, el->fsrv.child_kill_signal);
     if (el->fsrv.fsrv_pid > 0) {
-      /* This must be SIGTERM, to allow the forkserver to reap the child before exiting. */
-      kill(el->fsrv.fsrv_pid, SIGTERM);
+      kill(el->fsrv.fsrv_pid, el->fsrv.fsrv_kill_signal);
       /* Make sure the forkserver does not end up as zombie. */
       waitpid(el->fsrv.fsrv_pid, NULL, 0);
     }

src/afl-fuzz.c

@@ -1359,7 +1359,9 @@ int main(int argc, char **argv_orig, char **envp) {
   #endif
 
   afl->fsrv.child_kill_signal =
-      parse_afl_kill_signal_env(afl->afl_env.afl_kill_signal, SIGKILL);
+      parse_afl_kill_signal(afl->afl_env.afl_child_kill_signal, SIGKILL);
+  afl->fsrv.fsrv_kill_signal =
+      parse_afl_kill_signal(afl->afl_env.afl_fsrv_kill_signal, SIGTERM);
 
   setup_signal_handlers();
   check_asan_opts(afl);

src/afl-showmap.c

@@ -866,6 +866,8 @@ static void usage(u8 *argv0) {
       "startup (in milliseconds)\n"
       "AFL_KILL_SIGNAL: Signal ID delivered to child processes on timeout, "
       "etc. (default: SIGKILL)\n"
+      "AFL_FORK_SERVER_KILL_SIGNAL: Signal delivered to fork server processes on termination"
+      "                             (default: SIGTERM)\n"
       "AFL_MAP_SIZE: the shared memory size for that target. must be >= the "
       "size the target was compiled for\n"
       "AFL_PRELOAD: LD_PRELOAD / DYLD_INSERT_LIBRARIES settings for target\n"
@@ -1259,7 +1261,9 @@ int main(int argc, char **argv_orig, char **envp) {
     be_quiet = save_be_quiet;
 
     fsrv->child_kill_signal =
-        parse_afl_kill_signal_env(getenv("AFL_KILL_SIGNAL"), SIGKILL);
+        parse_afl_kill_signal(getenv("AFL_KILL_SIGNAL"), SIGKILL);
+    fsrv->fsrv_kill_signal =
+        parse_afl_kill_signal(getenv("AFL_FORK_SERVER_KILL_SIGNAL"), SIGTERM);
 
     if (new_map_size) {
 

src/afl-tmin.c

@@ -881,6 +881,8 @@ static void usage(u8 *argv0) {
       "AFL_CRASH_EXITCODE: optional child exit code to be interpreted as crash\n"
       "AFL_FORKSRV_INIT_TMOUT: time spent waiting for forkserver during startup (in milliseconds)\n"
       "AFL_KILL_SIGNAL: Signal ID delivered to child processes on timeout, etc. (default: SIGKILL)\n"
+      "AFL_FORK_SERVER_KILL_SIGNAL: Signal delivered to fork server processes on termination\n"
+      "                             (default: SIGTERM)\n"
       "AFL_MAP_SIZE: the shared memory size for that target. must be >= the size\n"
       "              the target was compiled for\n"
       "AFL_PRELOAD:  LD_PRELOAD / DYLD_INSERT_LIBRARIES settings for target\n"
@@ -1196,7 +1198,10 @@ int main(int argc, char **argv_orig, char **envp) {
   }
 
   fsrv->child_kill_signal =
-      parse_afl_kill_signal_env(getenv("AFL_KILL_SIGNAL"), SIGKILL);
+      parse_afl_kill_signal(getenv("AFL_KILL_SIGNAL"), SIGKILL);
+  fsrv->fsrv_kill_signal =
+      parse_afl_kill_signal(getenv("AFL_FORK_SERVER_KILL_SIGNAL"), SIGTERM);
+
 
   if (getenv("AFL_CRASH_EXITCODE")) {