linux-kernel - Re: [PATCH] open: introduce O

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Date:	Thu, 27 Aug 2009 14:35:47 +0000
From:	Florian Weimer <fweimer@....de>
To:	Eric Blake <ebb9@....net>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	bug-coreutils@....org, bug-gnulib@....org,
	Ulrich Drepper <drepper@...hat.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] open: introduce O_NOSTD

* Eric Blake:

> int open_safer (const char *name, int flags, int mode)
> {
>   int fd = open (name, flags | O_CLOEXEC, mode);
>   if (0 <= fd && fd <= 2)
>     {
>       int dup = fcntl (fd, ((flags & O_CLOEXEC)
>                             ? F_DUPFD_CLOEXEC : F_DUPFD), 3);
>       int saved_errno = errno;
>       close (fd);
>       errno = saved_errno;
>       fd = dup;
>     }
>   else if (!(flags & O_CLOEXEC))
>     {
>       if ((flags = fcntl (fd, F_GETFD)) < 0
>           || fcntl (fd, F_SETFD, flags & ~FD_CLOEXEC) == -1)
>         {
>           int saved_errno = errno;
>           close (fd);
>           fd = -1;
>           errno = saved_errno;
>         }
>     }
>   return fd;
> }

> This solves the fd leak,

It's still buggy.  You need something like this:

int open_safer(const char *name, int flags, int mode)
{
  int opened_fd[3] = {0, 0, 0};
  int fd, i, errno_saved;
  while (1) {
    fd = open(name, flags | O_CLOEXEC, mode);
    if (fd < 0 || fd > 2) {
      break;
    }
    opened_fd[fd] = 1;
  }
  for (int i = 0; i <= 2; ++i) {
    if (opened_fd[i]) {
      errno_saved = errno;
      close(i);
      errno = errno_saved;
    }
  }
  return fd;
}

It's untested, so it's probably still buggy.

(O_CLOEXEC should have been a thread attribute, like the base path in
the *_at functions. *sigh*)

-- 
Florian Weimer                <fweimer@....de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstraße 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99
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