commit 36dd1443670c571fa9f4a8904479c6bd8e8444c6
author Josh Gao <jmgao@google.com> Thu Jul 14 16:05:10 2016 -0700
committer Josh Gao <jmgao@google.com> Mon Jul 18 19:35:45 2016 +0000
tree 6ef64d1329523a31da0e478043a92bd26ef83947
parent 71da8e7537b05f7e5b107e3f9f6476c2493f0cbc

DO NOT MERGE: debuggerd: verify that traced threads belong to the right process.

Fix two races in debuggerd's PTRACE_ATTACH logic:
  1. The target thread in a crash dump request could exit between the
     /proc/<pid>/task/<tid> check and the PTRACE_ATTACH.
  2. Sibling threads could exit between listing /proc/<pid>/task and the
     PTRACE_ATTACH.

Backport of NYC change I4dfe1ea30e2c211d2389321bd66e3684dd757591
Bug: http://b/29555636
Change-Id: I320f47216b21018d3f613cfbbaaff40b3548ef36

debuggerd/tombstone.cpp

diff --git a/debuggerd/tombstone.cpp b/debuggerd/tombstone.cpp
index 46f453b..3eeff34 100644
--- a/debuggerd/tombstone.cpp
+++ b/debuggerd/tombstone.cpp
@@ -412,7 +412,7 @@
     }
 
     // Skip this thread if cannot ptrace it
-    if (ptrace(PTRACE_ATTACH, new_tid, 0, 0) < 0) {
+    if (!ptrace_attach_thread(pid, new_tid)) {
       _LOG(log, logtype::ERROR, "ptrace attach to %d failed: %s\n", new_tid, strerror(errno));
       continue;
     }