Fw: Please evaluate my patch for Winbind

[Hannes Schmidt]

----- Original Message -----
From: "Hannes Schmidt" <mail at schmidt-net.via.t-online.de>
To: <samba at lists.samba.org>
Sent: Thursday, July 25, 2002 6:43 PM
Subject: [Samba] Please evaluate my patch for Winbind


> Yesterday I posted a problem report with some diagnostics. I seem to have
found a solution on my own
> and provide a patch here. [I didn't post this as a follow-up because
nobody responded to my original post
> and I wanted to make sure someone reads at least this one.]
>
> The patch makes the winbind client (libnss_winbind.so) code more robust.
>
> Consider the following fragment of broken application code.
>
> if( fork() == 0 ) {
>     /* child */
>     close( 0 );             /* next open() will return 0 (stdin) */
>     getpwent(...);        /* pid changed, so wb_common.c will open the
pipe to winbindd, the handle will be 0 */
>     fd = open( ... );     /* returned fd isn't 0 although the code assumes
this */
>     execve( ... );         /* executed program reads from stdin which -
unintentionally - is the winbind pipe */
> } else {
>     /* parent */
>     ...
> }
>
> Obviously, this code is broken and could be easily fixed by doing the
getpwent() before the close(). Unfortunately
> the version of cron installed on my system is broken in a more complex but
similar way. There is probably more
> broken code like this in other standard unix software, especially since
it's such a subtle mistake.
>
> The provided patch to wb_common.c makes sure that the handle to the
winbindd pipe is not 0, 1 or 2.
> Even if this is complete crap, I would appreciate any feedback.
>
> *** /root/samba-2.2.5/source/nsswitch/wb_common.c Wed Jun 19 03:13:44 2002
> --- wb_common.c Thu Jul 25 16:36:39 2002
> ***************
> *** 94,99 ****
> --- 94,120 ----
>    }
>   }
>
> + /* Returns a duplicate of the given file descriptor that is guranteed
> +    not to be 0, 1 or 2 (stdin, stdout or stderr respectively), unless
> +    an error occurs. If the given fd is invalid, it will be returned
> +    unchanged. If a different error occurs, the returned file handle
> +    will still be valid but it may be 0, 1 or 2. If a valid file
> +    handle is returned and the returned handle is different to the
> +    original one, the original one will be closed. If dup() is broken,
> +    this function might never return. */
> +
> + int make_nonstd_fd(int fd)
> + {
> +  int saved_fd;
> +  if (0 >= fd && fd <= 2) {
> +      fd = dup(saved_fd = fd);
> +      if (fd == -1) return saved_fd;
> +      fd = make_nonstd_fd(fd);
> +      close(saved_fd);
> +  }
> +  return fd;
> + }
> +
>   /* Connect to winbindd socket */
>
>   int winbind_open_pipe_sock(void)
> ***************
> *** 158,164 ****
>    if ((winbindd_fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
>     return -1;
>    }
> !
>    if (connect(winbindd_fd, (struct sockaddr *)&sunaddr,
>         sizeof(sunaddr)) == -1) {
>     close_sock();
> --- 179,188 ----
>    if ((winbindd_fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
>     return -1;
>    }
> !
> !  winbindd_fd = make_nonstd_fd( winbindd_fd );
> !
> !
>    if (connect(winbindd_fd, (struct sockaddr *)&sunaddr,
>         sizeof(sunaddr)) == -1) {
>     close_sock();
> ***************
> *** 167,172 ****
> --- 191,197 ----
>
>    return winbindd_fd;
>   }
> +
>
>   /* Write data to winbindd socket */
>
>
>
>
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