unix: don't close fd immediately after dup2() in uv_spawn()

[bnoordhuis]

Test case:

var fd = require('fs').openSync('/dev/tty', 'w');
require('child_process').spawn('/bin/false', [], { stdio: ['ignore', fd, fd] });

$ strace node t.js
$ strace -fe open,dup2 out/Release/node tmp/t.js
<snip>
[pid 19418] open("/dev/tty", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 9
<snip>
[pid 19424] dup2(9, 1)                  = 1
[pid 19424] dup2(9, 2)                  = -1 EBADF (Bad file descriptor)
<snip>

[indutny]

Mind if I'll take a look at it?

[bnoordhuis]

Sure, go ahead.

[bnoordhuis]

I'm reasonably sure the patch below fixes it but I'm unsure as to how correct it is. It passes all node and libuv tests but that doesn't mean it doesn't have bugs, of course.

diff --git a/src/unix/process.c b/src/unix/process.c
index 990ea15..4d86089 100644
--- a/src/unix/process.c
+++ b/src/unix/process.c
@@ -285,8 +285,10 @@ static void uv__process_child_init(const uv_process_options_t* options,
     close_fd = pipes[fd][0];
     use_fd = pipes[fd][1];

-    if (use_fd >= 0)
-      close(close_fd);
+    if (use_fd >= 0) {
+      if (close_fd != -1)
+        close(close_fd);
+    }
     else if (fd >= 3)
       continue;
     else {
@@ -304,15 +306,22 @@ static void uv__process_child_init(const uv_process_options_t* options,

     if (fd == use_fd)
       uv__cloexec(use_fd, 0);
-    else {
+    else
       dup2(use_fd, fd);
-      close(use_fd);
-    }

     if (fd <= 2)
       uv__nonblock(fd, 0);
   }

+  for (fd = 0; fd < stdio_count; fd++) {
+    if (fd >= 3)
+      break;
+
+    use_fd = pipes[fd][1];
+    if (fd != use_fd)
+      close(use_fd);
+  }
+
   if (options->cwd != NULL && chdir(options->cwd)) {
     uv__write_int(error_fd, -errno);
     perror("chdir()");

[indutny]

@bnoordhuis LGTM

[bnoordhuis]

I found another bug in uv__process_child_init(), let me follow up with a more thorough patch.