Set FD_CLOEXEC flag on stdio FDs before spawning.

With regression test.

src/node_child_process.cc

@@ -39,6 +39,16 @@ static inline int SetNonBlocking(int fd) {
 }
 
 
+static inline int SetCloseOnExec(int fd) {
+  int flags = fcntl(fd, F_GETFD, 0);
+  int r = fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
+  if (r != 0) {
+    perror("SetCloseOnExec()");
+  }
+  return r;
+}
+
+
 static inline int ResetFlags(int fd) {
   int flags = fcntl(fd, F_GETFL, 0);
   // blocking
@@ -223,6 +233,22 @@ int ChildProcess::Spawn(const char *file,
     return -1;
   }
 
+  // Set the close-on-exec FD flag
+  if (custom_fds[0] == -1) {
+    SetCloseOnExec(stdin_pipe[0]);
+    SetCloseOnExec(stdin_pipe[1]);
+  }
+
+  if (custom_fds[1] == -1) {
+    SetCloseOnExec(stdout_pipe[0]);
+    SetCloseOnExec(stdout_pipe[1]);
+  }
+
+  if (custom_fds[2] == -1) {
+    SetCloseOnExec(stderr_pipe[0]);
+    SetCloseOnExec(stderr_pipe[1]);
+  }
+
   // Save environ in the case that we get it clobbered
   // by the child process.
   char **save_our_env = environ;

test/simple/test-child-process-double-pipe.js

@@ -0,0 +1,71 @@
+var assert   = require('assert'),
+    util   = require('util'),
+    spawn = require('child_process').spawn;
+
+// We're trying to reproduce:
+// $ echo -e "hello\nnode\nand\nworld" | grep o | sed s/o/a/
+
+var
+  echo    = spawn('echo', ['-e', 'hello\nnode\nand\nworld\n']),
+  grep  = spawn('grep', ['o']),
+  sed  = spawn('sed', ['s/o/O/']);
+
+/*
+ * grep and sed hang if the spawn function leaks file descriptors to child
+ * processes.
+ * This happens when calling pipe(2) and then forgetting to set the
+ * FD_CLOEXEC flag on the resulting file descriptors.
+ *
+ * This test checks child processes exit, meaning they don't hang like
+ * explained above.
+ */
+
+
+
+// pipe echo | grep
+echo.stdout.on('data', function (data) {
+  if (!grep.stdin.write(data)) {
+    echo.stdout.pause();
+  }
+});
+
+grep.stdin.on('drain', function (data) {
+  echo.stdout.resume();
+});
+
+// propagate end from echo to grep
+echo.stdout.on('end', function (code) {
+  grep.stdin.end();
+});
+
+
+
+// pipe grep | sed
+grep.stdout.on('data', function (data) {
+  if (!sed.stdin.write(data)) {
+    grep.stdout.pause();
+  }
+});
+
+sed.stdin.on('drain', function (data) {
+  grep.stdout.resume();
+});
+
+// propagate end from grep to sed
+grep.stdout.on('end', function (code) {
+  sed.stdin.end();
+});
+
+
+
+var result = '';
+
+// print sed's output
+sed.stdout.on('data', function (data) {
+  result += data.toString('utf8', 0, data.length);
+  util.print(data);
+});
+
+sed.stdout.on('end', function (code) {
+  assert.equal(result, 'hellO\nnOde\nwOrld\n');
+});