Messages in this thread | | | Date | Tue, 22 Jun 1999 01:54:28 -0400 (EDT) | From | Alexander Viro <> | Subject | Re: immutable flag on ext2fs |
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On Mon, 21 Jun 1999, Mike A. Harris wrote:
> >FreeBSD does it through single user mode, which I beleive is inappropriate > >since you may want to make system file changes on the fly. > > Single user mode doesn't have networking up, so there should only > be local consoles to begin with. Or is FreeBSD's single user > mode different? Granted, one can edit the initscripts to do
It's not single-user. Quoth the Daemon Book:
>>>Security levels are defined as follows:
-1. Permanently insecure mode: Always run system in level 0 mode (must be compiled into the kernel).
0. Insecure mode: Immutable and append-only flags may be turned off. All devices can be read or written, subject to their permissions.
1. Secure mode: The superuser-settable immutable and append-only flags cannot be cleared; disks for mounted filesystems and kernel memory (/dev/mem and /dev/kmem) are read-only.
2. Highly secure mode: This mode is the same as secure mode, except that disks are always read-only whether mounted or not. This level precludes even a superuser from tampering with filesystems by unmounting them, but also inhibits formatting of new filesystems.
Normally the system runs with level 0 security while in single-user mode, and with level 1 security while in multiuser mode. If level 2 security is desired while the system is running in multiuser mode, it should be set in /etc/rc startup script<<<
superuser-settable flags are not supported in Linux right now. The idea being: there are two immutable flags - user and root. For VFS they are the same (i.e. presense of any makes file immutable). user flag can be set/reset by owner of file and by root. root flag can be changed *only* by root and only if securelevel < 1. In other words, immutable is available for users, but root can additionally set stronger variant that can't be revoked without rebooting into insecure mode. The same goes for append-only. *Good* idea, but unfortunately ext2 doesn't support it.
> whatever, but I can't see it making a machine more secure. Spend > the time putting up a proper firewall, and using "good" security > techniques instead. Security through obscurity is none at all.
It is not a security through obscurity. It doesn't close all holes (as any other measure), but it's a useful additional tool.
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