Make Linux signal handler more robust.

Breakpad can be used on processes where a mistaken
library saves then restores one of our signal handlers
with 'signal' instead of 'sigaction'.

This loses the SA_SIGINFO flag associated with the 
Breakpad handler, and in some cases (e.g. Android/ARM
kernels), the values of the 'info' and 'uc' parameters
that ExceptionHandler::SignalHandler() receives will
be completely bogus, leading to a crash when the function
is executed (and of course, no minidump generation).

To work-around this, have SignalHandler() check the state
of the flag. If it is incorrectly unset, re-register with
'sigaction' and the correct flag, then return. The signal
will be re-thrown, and this time the function will be
called with the correct values.
Review URL: https://breakpad.appspot.com/481002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1067 4c0a9323-5329-0410-9bdc-e9ce6186880e

1 files changed, 31 insertions, 0 deletions

diff --git a/src/client/linux/handler/exception_handler_unittest.cc b/src/client/linux/handler/exception_handler_unittest.cc
index 890061e6..bb463510 100644
--- a/src/client/linux/handler/exception_handler_unittest.cc
+++ b/src/client/linux/handler/exception_handler_unittest.cc
@@ -317,6 +317,37 @@ TEST(ExceptionHandlerTest, RedeliveryToDefaultHandler) {
   ASSERT_NO_FATAL_FAILURE(WaitForProcessToTerminate(child, SIGSEGV));
 }
 
+// Check that saving and restoring the signal handler with 'signal'
+// instead of 'sigaction' doesn't make the Breakpad signal handler
+// crash. See comments in ExceptionHandler::SignalHandler for full
+// details.
+TEST(ExceptionHandlerTest, RedeliveryOnBadSignalHandlerFlag) {
+  AutoTempDir temp_dir;
+  const pid_t child = fork();
+  if (child == 0) {
+    // Install the RaiseSIGKILL handler for SIGSEGV.
+    ASSERT_TRUE(InstallRaiseSIGKILL());
+
+    // Create a new exception handler, this installs a new SIGSEGV
+    // handler, after saving the old one.
+    ExceptionHandler handler(
+        MinidumpDescriptor(temp_dir.path()), NULL,
+        DoneCallbackReturnFalse, NULL, true, -1);
+
+    // Install the default SIGSEGV handler, saving the current one.
+    // Then re-install the current one with 'signal', this loses the
+    // SA_SIGINFO flag associated with the Breakpad handler.
+    sighandler_t old_handler = signal(SIGSEGV, SIG_DFL);
+    ASSERT_NE(old_handler, SIG_ERR);
+    ASSERT_NE(signal(SIGSEGV, old_handler), SIG_ERR);
+
+    // Crash with the exception handler in scope.
+    *reinterpret_cast<volatile int*>(NULL) = 0;
+  }
+  // SIGKILL means Breakpad's signal handler didn't crash.
+  ASSERT_NO_FATAL_FAILURE(WaitForProcessToTerminate(child, SIGKILL));
+}
+
 TEST(ExceptionHandlerTest, StackedHandlersDeliveredToTop) {
   AutoTempDir temp_dir;