Prevent crashes if a map cannot be created.

Under some conditions, /proc/<pid>/maps might return nothing. If we
try and unwind in this case, we'll crash. Check this case and fail
the unwind.

Add checks that no other functions try and use map_ without
checking for nullptr.

Add logging when an unwind fails so it's clear what happened.

Bug: 21162746
Change-Id: I56ce51dda0cfc9db20475a441f118108196aa07c

1 files changed, 5 insertions, 0 deletions

diff --git a/libbacktrace/BacktraceCurrent.cpp b/libbacktrace/BacktraceCurrent.cpp
index 14f04de5e..95cd4d1a6 100644
--- a/libbacktrace/BacktraceCurrent.cpp
+++ b/libbacktrace/BacktraceCurrent.cpp
@@ -65,6 +65,11 @@ size_t BacktraceCurrent::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
 }
 
 bool BacktraceCurrent::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
+  if (GetMap() == nullptr) {
+    // Without a map object, we can't do anything.
+    return false;
+  }
+
   if (ucontext) {
     return UnwindFromContext(num_ignore_frames, ucontext);
   }