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FreeBSD Security Archives: Re: kern.securelevel and X

Re: kern.securelevel and X

Justin Wells (jreadsemiotek.com)
Mon, 18 Oct 1999 11:01:13 -0400

OK... but why was mount excepted in the first place? What I meant by
"not confident that I understand all the different implications" is
that I don't know what the reason for excluding mount was in the
first place.

Justin

On Mon, Oct 18, 1999 at 10:56:51AM +0200, Dag-Erling Smorgrav wrote:
> Justin Wells <jreadsemiotek.com> writes:
> > On Mon, Oct 18, 1999 at 09:55:32AM +0200, Dag-Erling Smorgrav wrote:
> > > Well, then, fix mount(8) so it won't run at high securelevels. You
> > > know where to find the source code.
> > It's mount(2) that has to be fixed. I suppose I could go and look at
> > it, but I'm not confident that I understand all the different
> > implications of the securelevel stuff at that level.
>
> Here's an untested patch for -CURRENT which will make mount(2) fail
> with EPERM if running at securelevel 4 or higher. Took me all of three
> minutes to throw together.
>
> Index: vfs_syscalls.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/kern/vfs_syscalls.c,v
> retrieving revision 1.138
> diff -u -r1.138 vfs_syscalls.c
> --- vfs_syscalls.c 1999/10/03 12:18:14 1.138
> +++ vfs_syscalls.c 1999/10/18 08:52:56
> -123,6 +123,8
>
> if (usermount == 0 && (error = suser(p)))
> return (error);
> + if (securelevel > 3)
> + return (EPERM);
> /*
> * Do not allow NFS export by non-root users.
> */
>
> I'm starting to think that secure levels should be implemented as
> bitmasks, with one bit for each operation or group of operation to be
> allowed or denied (0 = allow, 1 = deny). The if statement above could
> be rewritten as:
>
> if (securemask & SEC_MOUNT)
> return (EPERM);
>
> Using a simple bitmask might be too simple though (it would restrict
> us to 32 or 64 distinct operations), so we might want to hide the
> actual implementation behind a function call or macro:
>
> if (!sec_permitted(SEC_MOUNT))
> return (EPERM);
>
> DES
> --
> Dag-Erling Smorgrav - desflood.ping.uio.no

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This archive was generated by hypermail 2.0b3 on Mon Oct 18 1999 - 10:01:34 CDT