From f6fa1ae2f5b17151abee45369afc9c6a8d89d1d6 Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Mon, 2 May 2016 08:48:46 +0000
Subject: spawn: proper signal handling for vfork

We cannot afford to fire Perl-level signal handlers in the
vforked child process since they're not designed to run in
the child like that.

Thus we need to block all signals before calling vfork, reset
signal dispositions in the child, and restore the signal mask in
the parent.

ref: https://ewontfix.com/7
---
 lib/PublicInbox/Spawn.pm | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

(limited to 'lib')

diff --git a/lib/PublicInbox/Spawn.pm b/lib/PublicInbox/Spawn.pm
index 23f303fb..c5a5c012 100644
--- a/lib/PublicInbox/Spawn.pm
+++ b/lib/PublicInbox/Spawn.pm
@@ -24,6 +24,8 @@ my $vfork_spawn = <<'VFORK_SPAWN';
 #include <sys/uio.h>
 #include <unistd.h>
 #include <alloca.h>
+#include <signal.h>
+#include <assert.h>
 
 #define AV_ALLOCA(av, max) alloca((max = (av_len((av)) + 1)) * sizeof(char *))
 
@@ -81,6 +83,8 @@ int public_inbox_fork_exec(int in, int out, int err,
 	pid_t pid;
 	char **argv, **envp;
 	I32 max;
+	sigset_t set, old;
+	int ret;
 
 	argv = AV_ALLOCA(cmd, max);
 	av2c_copy(argv, cmd, max);
@@ -88,14 +92,26 @@ int public_inbox_fork_exec(int in, int out, int err,
 	envp = AV_ALLOCA(env, max);
 	av2c_copy(envp, env, max);
 
+	ret = sigfillset(&set);
+	assert(ret == 0 && "BUG calling sigfillset");
+	ret = sigprocmask(SIG_SETMASK, &set, &old);
+	assert(ret == 0 && "BUG calling sigprocmask to block");
 	pid = vfork();
 	if (pid == 0) {
+		int sig;
+
 		REDIR(in, 0);
 		REDIR(out, 1);
 		REDIR(err, 2);
+		for (sig = 1; sig < NSIG; sig++)
+			signal(sig, SIG_DFL); /* ignore errorrs on signals */
+		ret = sigprocmask(SIG_SETMASK, &old, NULL);
+		if (ret != 0) xerr("sigprocmask failed in vfork child");
 		execve(filename, argv, envp);
 		xerr("execve failed");
 	}
+	ret = sigprocmask(SIG_SETMASK, &old, NULL);
+	assert(ret == 0 && "BUG calling sigprocmask to restore");
 
 	return (int)pid;
 }
@@ -111,7 +127,7 @@ if (defined $vfork_spawn) {
 		my $f = "$inline_dir/.public-inbox.lock";
 		open my $fh, '>', $f or die "failed to open $f: $!\n";
 		flock($fh, LOCK_EX) or die "LOCK_EX failed on $f: $!\n";
-		eval 'use Inline C => $vfork_spawn';
+		eval 'use Inline C => $vfork_spawn'; #, BUILD_NOISY => 1';
 		my $err = $@;
 		flock($fh, LOCK_UN) or die "LOCK_UN failed on $f: $!\n";
 		die $err if $err;
-- 
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