Commit 2bf886af authored Mar 16, 2020 by Tom Cherry

init: use a no-op signal handler instead of SIG_IGN for SIGPIPE

We want to ignore SIGPIPE within init, but if we use SIG_IGN, that
would be inherited by child processes through exec(), which we do not
want to have happen.  We instead set up a real signal handler with a
no-op handler function, that will ignore SIGPIPE within init, but will
not be inherited across exec().

This fixes c29c2baa ("init: Add support for native service
registration with lmkd"), when SIG_IGN was introduced.
Note that we caught this issue before shipping a release with that
change, so the major motivation here is to not cause a behavior change
in init.

Bug: 151581751
Test: children of init that don't explicitly block SIGPIPE exit when
      sent SIGPIPE
Test: children of init that do explicitly block SIGPIPE do not exit
      when sent SIGPIPE
Test: init does not exit when sent SIGPIPE
Test: init exits when sent SIGABRT
Merged-In: Ieda8555fd03836bcd672a422fe673a8369ad9beb
Change-Id: Ieda8555fd03836bcd672a422fe673a8369ad9beb
(cherry picked from commit fd470e87)

parent c2872d83

init/init.cpp

+9 −2

Original line number	Diff line number	Diff line
		@@ -713,8 +713,15 @@ int SecondStageMain(int argc, char** argv) {
		InitKernelLogging(argv);
		LOG(INFO) << "init second stage started!";

		// Will handle EPIPE at the time of write by checking the errno
		signal(SIGPIPE, SIG_IGN);
		// Init should not crash because of a dependence on any other process, therefore we ignore
		// SIGPIPE and handle EPIPE at the call site directly. Note that setting a signal to SIG_IGN
		// is inherited across exec, but custom signal handlers are not. Since we do not want to
		// ignore SIGPIPE for child processes, we set a no-op function for the signal handler instead.
		{
		struct sigaction action = {.sa_flags = SA_RESTART};
		action.sa_handler = [](int) {};
		sigaction(SIGPIPE, &action, nullptr);
		}

		// Set init and its forked children's oom_adj.
		if (auto result =