libdebuggerd_handler: in-process crash dumping for seccomped processes.

Do an in-process unwind for processes that have PR_SET_NO_NEW_PRIVS
enabled.

Bug: http://b/34684590
Test: debuggerd_test, killall -ABRT media.codec
Change-Id: I62562ec2c419d6643970100ab1cc0288982a1eed

1 files changed, 14 insertions, 8 deletions

diff --git a/debuggerd/handler/debuggerd_handler.cpp b/debuggerd/handler/debuggerd_handler.cpp
index b1dc01aca..680ba4bee 100644
--- a/debuggerd/handler/debuggerd_handler.cpp
+++ b/debuggerd/handler/debuggerd_handler.cpp
@@ -62,6 +62,8 @@
 
 #define CRASH_DUMP_PATH "/system/bin/" CRASH_DUMP_NAME
 
+extern "C" bool debuggerd_fallback(ucontext_t*, siginfo_t*, void*);
+
 static debuggerd_callbacks_t g_callbacks;
 
 // Mutex to ensure only one crashing thread dumps itself.
@@ -329,7 +331,7 @@ static void resend_signal(siginfo_t* info, bool crash_dump_started) {
 
 // Handler that does crash dumping by forking and doing the processing in the child.
 // Do this by ptracing the relevant thread, and then execing debuggerd to do the actual dump.
-static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*) {
+static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void* context) {
   int ret = pthread_mutex_lock(&crash_mutex);
   if (ret != 0) {
     __libc_format_log(ANDROID_LOG_INFO, "libc", "pthread_mutex_lock failed: %s", strerror(ret));
@@ -359,18 +361,22 @@ static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*)
 
   log_signal_summary(signal_number, info);
 
+  void* abort_message = nullptr;
+  if (g_callbacks.get_abort_message) {
+    abort_message = g_callbacks.get_abort_message();
+  }
+
   if (prctl(PR_GET_NO_NEW_PRIVS, 0, 0, 0, 0) == 1) {
-    // The process has NO_NEW_PRIVS enabled, so we can't transition to the crash_dump context.
-    __libc_format_log(ANDROID_LOG_INFO, "libc",
-                      "Suppressing debuggerd output because prctl(PR_GET_NO_NEW_PRIVS)==1");
+    ucontext_t* ucontext = static_cast<ucontext_t*>(context);
+    if (signal_number == DEBUGGER_SIGNAL || !debuggerd_fallback(ucontext, info, abort_message)) {
+      // The process has NO_NEW_PRIVS enabled, so we can't transition to the crash_dump context.
+      __libc_format_log(ANDROID_LOG_INFO, "libc",
+                        "Suppressing debuggerd output because prctl(PR_GET_NO_NEW_PRIVS)==1");
+    }
     resend_signal(info, false);
     return;
   }
 
-  void* abort_message = nullptr;
-  if (g_callbacks.get_abort_message) {
-    abort_message = g_callbacks.get_abort_message();
-  }
   // Populate si_value with the abort message address, if found.
   if (abort_message) {
     info->si_value.sival_ptr = abort_message;