Date: Sun, 14 Mar 1999 06:50:11 -0700 From: Wes Peters <wes@softweyr.com> To: Peter Jeremy <peter.jeremy@auss2.alcatel.com.au> Cc: freebsd-security@FreeBSD.ORG Subject: Re: disapointing security architecture Message-ID: <36EBBE93.DEC82C92@softweyr.com> References: <99Mar14.193150est.40323@border.alcanet.com.au>
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Peter Jeremy wrote:
>
> Wes Peters <wes@softweyr.com> wrote:
> >My suggestion for FreeBSD would be to steal half of the disk direct
> >blocks in the disk inode for ACL information.
>
> The downside of this is that _all_ files between 7 and 12 blocks long
> (typically 48-96KB) will then need an indirect block - adding an extra
> block to its size (additional indirect blocks are needed for other
> sizes as well, but this first one is the biggest relative space/time
> hit). Whilst this may be reasonable for a system where the majority
> of the files have individual ACLs, I suspect this wouldn't be true
> of most systems.
Actually, only the ones that have ACLs will take this hit, since
you don't have to reserve the space if the file type isn't "file with
ACL." I see a couple of holes in this theory, though: you need ACLs
on device files too, and it becomes very expensive to add an ACL to
a file after the fact, since you have to "push down" all the blocks
in order to clear the ACL entries.
> IMHO, stealing an extra inode (or disk block) only for files that need
> ACLs would be preferable (especially if ACL sharing is implemented).
I agree, but I'm not sure how you would express the ACL sharing idea to
the user. When the user adds an ACL to a file, are you just going to
exhaustively search all existing ACLs to see if one matches? What do
you do if two files are sharing an ACL and a user edits one? Change
both? Split a new ACL?
> Admittedly, we still need to find space for the additional pointer
> in the inode.
The ufs dinode has two "spare" int32_t's at the end, that should do it.
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
http://www.softweyr.com/~softweyr wes@softweyr.com
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