Disallow disabling DisableDebuggerAttachment on runnning Tor

Also, have tor_disable_debugger_attach() return a tristate of
success/failure/don't-know-how , and only log appropriately.

doc/tor.1.txt

@@ -282,8 +282,8 @@ Other options can be specified either on the command-line (--option
    to alter the system wide ptrace scope as it may not even exist. If you wish
    to attach to Tor with a debugger such as gdb or strace you will want to set
    this to 0 for the duration of your debugging. Normal users should leave it
-   on. (Default: 1)
- 
+   on. Disabling this option while Tor is running is prohibited. (Default: 1)
+
 **FetchDirInfoEarly** **0**|**1**::
     If set to 1, Tor will always fetch directory information like other
     directory caches, even if you don't meet the normal criteria for fetching

src/common/compat.c

@@ -1542,8 +1542,8 @@ switch_id(const char *user)
  * CAP_SYS_PTRACE and so it is very likely that root will still be able to
  * attach to the Tor process.
  */
-/** Attempt to disable debugger attachment: return 0 on success, -1 on
- * failure. */
+/** Attempt to disable debugger attachment: return 1 on success, -1 on
+ * failure, and 0 if we don't know how to try on this platform. */
 int
 tor_disable_debugger_attach(void)
 {
@@ -1568,11 +1568,12 @@ tor_disable_debugger_attach(void)
 
   // XXX: TODO - Mac OS X has dtrace and this may be disabled.
   // XXX: TODO - Windows probably has something similar
-  if (r == 0) {
+  if (r == 0 && attempted) {
     log_debug(LD_CONFIG,"Debugger attachment disabled for "
               "unprivileged users.");
+    return 1;
   } else if (attempted) {
-    log_warn(LD_CONFIG, "Unable to disable ptrace attach: %s",
+    log_warn(LD_CONFIG, "Unable to disable debugger attaching: %s",
              strerror(errno));
   }
   return r;

src/or/config.c

@@ -1326,12 +1326,26 @@ options_act(const or_options_t *old_options)
   const int transition_affects_workers =
     old_options && options_transition_affects_workers(old_options, options);
 
-   /* disable ptrace and later, other basic debugging techniques */
-  if (options->DisableDebuggerAttachment) {
-    tor_disable_debugger_attach();
-  } else {
-    log_notice(LD_CONFIG,"Debugger attachment enabled "
-               "for unprivileged users.");
+  /* disable ptrace and later, other basic debugging techniques */
+  {
+    /* Remember if we already disabled debugger attachment */
+    static int disabled_debugger_attach = 0;
+    /* Remember if we already warned about being configured not to disable
+     * debugger attachment */
+    static int warned_debugger_attach = 0;
+    if (options->DisableDebuggerAttachment && !disabled_debugger_attach) {
+      int ok = tor_disable_debugger_attach();
+      if (warned_debugger_attach && ok == 1) {
+        log_notice(LD_CONFIG, "Disabled attaching debuggers for unprivileged "
+                   "users.");
+      }
+      disabled_debugger_attach = (ok == 1);
+    } else if (!options->DisableDebuggerAttachment &&
+               !warned_debugger_attach) {
+      log_notice(LD_CONFIG, "Not disabling debugger attaching for "
+                 "unprivileged users.");
+      warned_debugger_attach = 1;
+    }
   }
 
   if (running_tor && !have_lockfile()) {
@@ -4170,6 +4184,13 @@ options_transition_allowed(const or_options_t *old,
     return -1;
   }
 
+  if (old->DisableDebuggerAttachment &&
+      !new_val->DisableDebuggerAttachment) {
+    *msg = tor_strdup("While Tor is running, disabling "
+                      "DisableDebuggerAttachment is not allowed.");
+    return -1;
+  }
+
   return 0;
 }