i386/87208: /dev/cuad[0/1] bad file descriptor error during mgetty read

[Bruce Evans]

On Tue, 18 Oct 2005, HASHI Hiroaki wrote:

> In this case, mgetty open a /dev/cuad? and dup(2) to stdin.
>
>     int fd;
>
>     fd = open(devname, O_RDWR | O_NDELAY | O_NOCTTY );
>
>     /* make new fd == stdin if it isn't already */
>
>     if (fd > 0)
>     {
>         (void) close(0);
> --->    if (dup(fd) != 0)
>         {
>             lprintf( L_FATAL, "mod: cannot make %s stdin", devname );
>             return ERROR;
>         }
>     }
>
> Bad dup() was not return descriptor 0.
>
> Is this a dup(3)'s bug?
> (or imcompatible change?)

Looks like a bug in dup(2).  dup(2) is documented to return the "lowest
numbered descriptor not in use by the process", and the close(0) should
ensure that descriptor 0 is not in use.  The only visible bug in mgetty
is that it ignores errors in close(0); this breaks mainly the error
reporting.

Bruce