Re: O_NOACCESS?

From: andi payn (andi_payn_at_speedymail.org)
Date: 10/31/03

  • Next message: M. Warner Losh: "Re: O_NOACCESS?" 
    To: "M. Warner Losh" <imp@bsdimp.com>
Date: Fri, 31 Oct 2003 13:20:33 -0800

    On Fri, 2003-10-31 at 12:02, M. Warner Losh wrote:
    > In message: <1067628015.825.64.camel@verdammt.falcotronic.net>
    > andi payn <andi_payn@speedymail.org> writes:
    > : On Fri, 2003-10-31 at 08:27, David Malone wrote:
    > : > On Thu, Oct 30, 2003 at 07:46:38AM -0800, andi payn wrote:
    > : > > In FreeBSD, this doesn't work; you just get EINVAL.
    > : >
    > : > I believe this is because of a security problem discovered a few
    > : > years ago, where you could open a file like /dev/io for neither
    > : > read nor write but still get the special privelages associated with
    > : > having the file open.
    > : >
    > : > If you were to allow people to open files without read or write
    > : > permission you'd need to fix problems like this in a different way.
    > :
    > : It seems to me that the right way to fix this is to ensure that only the
    > : superuser can open /dev/io device, no matter what permissions are on it.
    >
    > This might not be a bad idea, but it would force at least one company
    > (mine) to rewrite at least some of their software to run as root. we
    > currently don't run some things as root because we don't trust them.
    > But then you are getting into special case kludges. Better to require
    > that it is opened read or write permissions.

    Well, the io(4) manpage says:
    > In addition to any file access permissions on /dev/io, the kernel
    > enforces that only the super-user may open this device.

    If this is not true--and especially if it's not true by design--then the
    manpage ought to be changed.

    If O_NOACCESS were added, and /dev/io were not changed to match the
    manpage, then it could instead be changed so that read-only access
    grants full I/O privileges, but no access does not?

    > : Are there any other special devices like this in FreeBSD?
    >
    > Rewind units on tape drives? If there's no access check done, and I
    > open the rewind unit as joe-smoe? The close code is what does the
    > rewind, and you don't have enough knowledge to know if the tape was
    > opened r/w there.

    Thanks; that's a good example. Do you have an example of a specific
    driver so I can look at the code and see what would need to be done?

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  • Next message: M. Warner Losh: "Re: O_NOACCESS?"

    Relevant Pages

    • Re: O_NOACCESS?
      ... :>: Are there any other special devices like this in FreeBSD? ... :> Rewind units on tape drives? ...
      (freebsd-hackers)
    • Re: O_NOACCESS?
      ... "M. Warner Losh" wrote: ... > Rewind units on tape drives? ... > open the rewind unit as joe-smoe? ...
      (freebsd-hackers)