Fix issues with Yama restrictions in FRIDA mode

frida_mode/README.md

@@ -288,6 +288,12 @@ ucomisd                                 2 ( 0.86%)
 * `AFL_FRIDA_STATS_INTERVAL` - The maximum frequency to output statistics
 information. Stats will be written whenever they are updated if the given
 interval has elapsed since last time they were written.
+* `AFL_FRIDA_TRACEABLE` - Set the child process to be traceable by any process
+to aid debugging and overcome the restrictions imposed by YAMA. Supported on
+Linux only. Permits a non-root user to use `gcore` or similar to collect a core
+dump of the instrumented target. Note that in order to capture the core dump you
+must set a sufficient timeout (using `-t`) to avoid `afl-fuzz` killing the
+process whilst it is being dumped.
 
 ## FASAN - Frida Address Sanitizer Mode
 Frida mode also supports FASAN. The design of this is actually quite simple and

frida_mode/frida.map

@@ -33,6 +33,7 @@
     js_api_set_stats_interval;
     js_api_set_stderr;
     js_api_set_stdout;
+    js_api_set_traceable;
 
   local:
     *;

frida_mode/include/entry.h

@@ -4,6 +4,7 @@
 #include "frida-gumjs.h"
 
 extern guint64  entry_point;
+extern gboolean traceable;
 extern gboolean entry_compiled;
 extern gboolean entry_run;
 
@@ -15,5 +16,7 @@ void entry_start(void);
 
 void entry_prologue(GumStalkerIterator *iterator, GumStalkerOutput *output);
 
+void entry_on_fork(void);
+
 #endif
 

frida_mode/src/entry.c

@@ -1,5 +1,9 @@
 #include <dlfcn.h>
 
+#if defined(__linux__) && !defined(__ANDROID__)
+  #include <sys/prctl.h>
+#endif
+
 #include "frida-gumjs.h"
 
 #include "debug.h"
@@ -16,6 +20,7 @@
 extern void __afl_manual_init();
 
 guint64  entry_point = 0;
+gboolean traceable = FALSE;
 gboolean entry_compiled = FALSE;
 gboolean entry_run = FALSE;
 
@@ -26,21 +31,48 @@ static void entry_launch(void) {
 
   /* Child here */
   entry_run = TRUE;
+  entry_on_fork();
   instrument_on_fork();
   seccomp_on_fork();
   stats_on_fork();
 
 }
 
+#if defined(__linux__) && !defined(__ANDROID__)
+void entry_on_fork(void) {
+
+  if (traceable) {
+
+    if (prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY) < 0) {
+
+      FATAL("Failed to PR_SET_PTRACER");
+
+    }
+
+  }
+
+}
+
+#else
+void entry_on_fork(void) {
+
+  if (set_dumpable) { WARNF("AFL_FRIDA_TRACEABLE unsupported"); }
+
+}
+
+#endif
+
 void entry_config(void) {
 
   entry_point = util_read_address("AFL_ENTRYPOINT");
+  if (getenv("AFL_FRIDA_TRACEABLE") != NULL) { traceable = TRUE; }
 
 }
 
 void entry_init(void) {
 
   OKF("entry_point: 0x%016" G_GINT64_MODIFIER "X", entry_point);
+  OKF("dumpable: [%c]", traceable ? 'X' : ' ');
 
   if (dlopen(NULL, RTLD_NOW) == NULL) { FATAL("Failed to dlopen: %d", errno); }
 

frida_mode/src/js/api.js

@@ -243,6 +243,12 @@ class Afl {
         const buf = Memory.allocUtf8String(file);
         Afl.jsApiSetStdOut(buf);
     }
+    /**
+     * See `AFL_FRIDA_TRACEABLE`.
+     */
+    static setTraceable() {
+        Afl.jsApiSetTraceable();
+    }
     static jsApiGetFunction(name, retType, argTypes) {
         const addr = Afl.module.getExportByName(name);
         return new NativeFunction(addr, retType, argTypes);
@@ -286,6 +292,7 @@ Afl.jsApiSetStatsFile = Afl.jsApiGetFunction("js_api_set_stats_file", "void", ["
 Afl.jsApiSetStatsInterval = Afl.jsApiGetFunction("js_api_set_stats_interval", "void", ["uint64"]);
 Afl.jsApiSetStdErr = Afl.jsApiGetFunction("js_api_set_stderr", "void", ["pointer"]);
 Afl.jsApiSetStdOut = Afl.jsApiGetFunction("js_api_set_stdout", "void", ["pointer"]);
+Afl.jsApiSetTraceable = Afl.jsApiGetFunction("js_api_set_traceable", "void", []);
 Afl.jsApiWrite = new NativeFunction(
 /* tslint:disable-next-line:no-null-keyword */
 Module.getExportByName(null, "write"), "int", ["int", "pointer", "int"]);

frida_mode/src/js/js_api.c

@@ -231,3 +231,9 @@ __attribute__((visibility("default"))) void js_api_set_stalker_ic_entries(
 
 }
 
+__attribute__((visibility("default"))) void js_api_set_traceable(void) {
+
+  traceable = TRUE;
+
+}
+

frida_mode/ts/lib/afl.ts

@@ -284,6 +284,13 @@ class Afl {
     Afl.jsApiSetStdOut(buf);
   }
 
+  /**
+   * See `AFL_FRIDA_TRACEABLE`.
+   */
+  public static setTraceable(): void {
+    Afl.jsApiSetTraceable();
+  }
+
   private static readonly jsApiAddExcludeRange = Afl.jsApiGetFunction(
     "js_api_add_exclude_range",
     "void",
@@ -431,6 +438,11 @@ class Afl {
     "void",
     ["pointer"]);
 
+  private static readonly jsApiSetTraceable = Afl.jsApiGetFunction(
+    "js_api_set_traceable",
+    "void",
+    []);
+
   private static readonly jsApiWrite = new NativeFunction(
     /* tslint:disable-next-line:no-null-keyword */
     Module.getExportByName(null, "write"),

include/envs.h

@@ -76,6 +76,7 @@ static char *afl_environment_variables[] = {
     "AFL_FRIDA_PERSISTENT_RET",
     "AFL_FRIDA_STATS_FILE",
     "AFL_FRIDA_STATS_INTERVAL",
+    "AFL_FRIDA_TRACEABLE",
     "AFL_FUZZER_ARGS",  // oss-fuzz
     "AFL_GDB",
     "AFL_GCC_ALLOWLIST",