debuggerd: if PR_GET_DUMPABLE=0, don't ask for dumping

PR_GET_DUMPABLE is used by an application to indicate whether or
not core dumps / PTRACE_ATTACH should work.

Security sensitive applications often set PR_SET_DUMPABLE to 0 to
disable core dumps, to avoid leaking sensitive memory to persistent
storage. Similarly, they also set PR_SET_DUMPABLE to zero to prevent
PTRACE_ATTACH from working, again to avoid leaking the contents
of sensitive memory.

Honor PR_GET_DUMPABLE when connecting to debuggerd. If an application
has said it doesn't want its memory dumped, then we shouldn't
ask debuggerd to dump memory on its behalf.

FORTIFY_SOURCE tests: Modify the fortify_source tests to set
PR_SET_DUMPABLE=0. This reduces the total runtime of
/data/nativetest/bionic-unit-tests/bionic-unit-tests32 from approx
53 seconds to 25 seconds. There's no need to connect to debuggerd
when running these tests.

Bug: 16513137

(cherry picked from commit be0e43b776)

Change-Id: I6e1a9bce564e94fc19893d639b15f38c549cabfa

linker/debugger.cpp

@@ -206,6 +206,15 @@ static bool have_siginfo(int signum) {
 }
 
 static void send_debuggerd_packet(siginfo_t* info) {
+  if (prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) == 0) {
+    // process has disabled core dumps and PTRACE_ATTACH, and does not want to be dumped.
+    // Honor that intention by not connecting to debuggerd and asking it
+    // to dump our internal state.
+    __libc_format_log(ANDROID_LOG_INFO, "libc",
+                      "Suppressing debuggerd output because prctl(PR_GET_DUMPABLE)==0");
+    return;
+  }
+
   int s = socket_abstract_client(DEBUGGER_SOCKET_NAME, SOCK_STREAM);
   if (s == -1) {
     __libc_format_log(ANDROID_LOG_FATAL, "libc", "Unable to open connection to debuggerd: %s",