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Access Control Lists In Linux Filesystems?
oracleofbargth asks: "Is there any project for implementing ACLs in the various filesystems supported under linux (ext2, ext3, etc...) that has the potential to become an official part of the kernel, rather than just a patch to it? The Linux ACL Project looks good, but is ext2 specific. Trustees also looks promising, but a system implemented in the filesystem itself would be preferable. RSBAC also has ACL capabilities, but on the whole goes a bit overboard in terms of what I'm looking for. Ideally, I need something that will work with ext3 so that the ACL information will be journaled."
I've worked with ten or twelve operating systems at the system administration level, and I've done so in academic, corporate, medical, and military-industrial settings.
.02 pence is so lenghty. I could rant some more, but I think I got the major point across - ACLs on a "rwxrwxrwx" system is like streamlining a 1954 Volkswagen Beetle.
Most of the proprietary Unices (if you count different *nixen as separate OSes, double the OS count given above) have their own lame, incompatible implementations of ACLs. These are typically layered over the antique Unix rwxrwxrwx scheme.
"rwx" is insufficient. People often exhort others to "think unix" - and when you are talking about pipes & I/O redirection, or any of the other wonderful features of Unix, that's great. But if you "think unix" to the extent that you can't see how fundamentally LAME the unix access control mechanisms are, you are crippling yourself. To put it in perspective, consider the IBM MVS file protection system RACF - in RACF, you cannot grant a user write permission without also granting read permission. This is partially because of the underlying architecture of MVS, but that doesn't mean it's not lame and restrictive. However, most hardcore mainframers literally cannot conceive of a situation where they'd want write and not read.
Novell has the most advanced and useful system of file attributes I am aware of. For example, "create" and "write" are separate - this allows the creation of dead-drop boxes; folders where a user can create a file but cannot afterwards modify it. If you can't conceive a situation where you could put this to use, you are "thinking unix" to the point of wearing blinders. NOTE: the forgoing statement will cause this post to be labeled "flamebait" and modded into oblivion by self-righteous Berkleyites >:^} while simultaneously generating dozens of "oh yeah name one" followups.
There are many other aspects of the Novell system of file protection and user rights that are very advanced. Consult your local guru, but I'll mention "rename inhibit" as one useful ability. If Stef Murky, excuse me, Jeff Mirkey, ever gets his MANOS opsystem going under the GPL I personally will immediately convert to his Novell-clone filesystem. Even DEC VMS does not compare, and the VMS access control mechanisms beat Unix hands down.
I don't recommend Novell because it's not Open Source and because the complexity of X500 or NDS type "directory" systems adds instability and management overhead that is seldom warranted to achieve concrete goals. That being said, as the world becomes increasingly networked the previous statement becomes increasingly less accurate.
LDAP interfaces to SQL backends like MySQL and Postgres will eventually be the way to go (but not today, and ADS will never fit the problem space). The one warning I would sound is that when you keep file data and file attributes in separate places - as many systems do - you markedly decrease the robustness of your system. User data in the user directory, file attributes in the file header, is a better idea. Just like it's a better idea to put the comments in the source code than in a separate documentation file (don't get me started about that stupid practice).
Sorry my
--Charlie
And it's journalling and quick. The only problem is that they're running on a fork of the kernel, so you have to either pray that large patches will take properly, or keep CVS'ing it.
http://linux-xfs.sgi.com/projects/xfs/
Ooh, and pre-release 0.9 is out. So, get it, or something.
-Yarn - Rio Karma: Excellent
--
Linux user since early January 1992.
That's not true. r controls whether you can read the directory (i.e. do ls in it). x controls whether you can cd into a directory or access any files in it. If both r and x are disabled, then you can neither ls a directory nor access any files in it. The Unix permission system has its problems but this is not one of them.
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If you think big enough, you'll never have to do it.
Let's say you have a directory full of files, and you need some people to be able to write to these files (which implies they'll also need to be able to read the files, to verify their changes), and you have another group of people who needs to be able to read the files. Everyone else in the organization should have NO access. This is the most complicated case.
Can this be done with standard Unix permissons? At first glance, you might think that you can't, because the only permissions provided in Unix are User (owner), Group, and Other (world). You can't control the access for a second group, which is what you need, right?
However, the answer is YES! You can do this. Here's how:
Create one group each for the people who need to be able to read the files, and write the files. For simplicity of the example, let's call the groups "read" and "write" respectively.
Now, add every user who needs read access to those files to the "read" group, and add all users who need write access to BOTH groups.
Now, create a top level directory, like this (only ownerships, permissions, and the name are shown for brevity):
drwxr-x--- root read topdir
# mkdir topdir
# chgrp read topdir
# chmod 750 topdir
Both groups we created can cd into this directory (because we added the "write" group to the "read" group, remember?). Now, under that directory, create one or more directories where your data will be stored, like this:
drwxrwsr-x root write datadir
# cd topdir
# mkdir datadir
# chgrp write datadir
# chmod 2775 datadir
The '2' sets the SGID bit on the directory, which forces all files created in this directory to be created group-owned by the "write" group (it copies the group ownership of the directory to all new files in it). It will also make new files created in this directory group writable by default (again, copying the group permissions from the directory).
You might also want to prevent users from deleting files they don't own, by setting the sticky bit on the directory, which will make the '2' a '3' instead.
Now, users in the "write" group can create and write to files in this directory, and users in the "read" group will be able to read them, because they will be readable by other (world). However, everyone else will NOT be able to read them, because in order to do so, they would have needed to be in the "read" group in order to cd into topdir to get to datadir (which is why we also included the users in the "write" group in the "read" group)!
Thus, your problem is solved. Do this for every directory where the groups of people who need each type of access are different. This is BETTER than ACLs because a) it is either the same amount of administrative effort than managing ACL's on a per-directory basis (but you manage group membership instead), or LESS administrative effort than managing ACLs on a per-file basis; and b) it FORCES you to organize your data heirarchically by who has access to it.
Get over ACLs... they are a waste of time and programming effort.
You could argue that you might want some third group of people to have write access ONLY, but the practical value of this is very limited. If you feel that you need this you are probably being silly or WAY too paranoid, even for a system administrator. Limiting people from reading data that they can over-write is generally nonsensical.
I don't deny that there are certain very narrow applications for that sort of access limitation, but the likelihood that such an application would also present the need to have groups with each of those access requirements (read, read/write, and write-only) seems rather slim.
Note to slashdot maintainers: PLEASE make the damn text box for typing comments into bigger! The one currently provided on the web form makes typing long comments especially painful. And allowing the CODE HTML tag would be nice too.
"However, ReiserFS is broken with NFS currently..."
/net/mp3 type nfs (rw,rsize=8192,wsize=8192,soft,addr=192.168.128.25 0)
/usr/local type reiserfs (rw)
really? i sure didn't notice:
phexro!Phaktory:~$ mount -tnfs
helix:/usr/local/share/audio/mp3 on
phexro!Phaktory:~$ ssh helix mount -treiserfs
phexro@helix's password:
/dev/hdc1 on
phexro!Phaktory:~$
or are you talking about something more subtle?
--
"...there was no information in yours."
nonsense. what do you call this?
"...i predict that your filesystem 'Won't ever see the light of day.'"
sounds like information to me.
and who says that humor is a waste of time? lauging is good for you.
besides which, you completely missed the point of my post; your project is vapor. you have no code (released, anyways, which is what counts), no name, nothing to show but a bunch of buzzwords thrown together in a slashdot post. you don't even have an empty sourceforge project.
now, you sound like you might have some good ideas. and as much as good ideas are necessary, good implementations are much more necessary. you'd be much better off helping integrate your ideas into an existing project. there are so many players in the next-linux-filesystem arena that even if you do manage to make a stable release, it will probably die due to one of the other projects.
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Agreed! UGO does not scale when you are talking about a centralized directory with tens of thousands of users in it. Especially the G and the O parts.
I also find it funny that everytime ACLs come up, someone posts "ACLs are bad because they are too complicated and the sysadmin can shoot himself in the foot". Which is fucking hilarious attitude towards Unix, where one of the central tenent is "The Sysadmin Can Blow His Leg Off, so be careful".
--
Business. Numbers. Money. People. Computer World.
This is a networked file system, but OpenAFS has excellent support for ACLs. I am personally using it at Carnegie Mellon and its used at a host of other places like MIT. And its not a patch but simply a module you compile for the kernel. I got it running on my linux system in 15 minutes. Also has excellent support for security (see Kerberos).
http://www.lwn.net/2001/0222/kernel.php3
ReiserFS and NFS. The various problems that have bit (a small number of) ReiserFS users in 2.4 are being cleared up. But one larger problem remains: ReiserFS, as shipped in 2.4, does not support NFS. That limitation gets in the way of quite a few people who would like to use ReiserFS, but who also need to be able to export their filesystems.
For the short term, those who are not afraid of kernel patches can have a look at this message from Neil Brown describing where to get the patches he has made available. They are still under development, but they provide "reasonable NFS service" in their current state.
The picture for the longer term is a bit less clear. Neil has a plan for proper support of NFS with ReiserFS, and for improving NFS service in general. It is, however, a large change, requiring tweaks to every filesystem which needs to support NFS. Filesystem changes tend to make kernel hackers nervous, especially in the middle of a stable kernel series. And, in fact, Alan Cox responded that he was not interested in such an extensive patch.
Those who are curious about the troubles with NFS should look at Neil's justification for the changes. It is a lengthy, detailed, and well-argued discussion of how the current NFS implementation fails to mesh well with the various Linux filesystems, and exactly what needs to be fixed to make things work better. It was persuasive enough that Alan agreed that the approach made sense - for the 2.5 kernel series.
Thus, the 2.4 kernel may never support exporting of ReiserFS filesystems over NFS. Those who need this capability will have to apply the patch themselves. That is, if the distributors do not apply the patch themselves before shipping the 2.4 kernel. SuSE, at least, applied such a patch when it shipped ReiserFS with 2.2, so it would not be surprising to see that happen again.
cpeterso
Perhaps my problem is that my exposure to ACLs has been primarily with NT and that can be *very* difficult to manage.
This was the primary objection that I saw on the kernel mailing list the last time it was discussed. While ACL's offer finer grain control of a system, they also make auditing much more difficult.
MOVE 'ZIG'.
and building the intranet in ASP.
At least use JSP. Then when Linux gets ACL or whatever you aren't locked in to the evil empire.
MOVE 'ZIG'.
One concept I would love to see implemented is "watchdogs." This is the ability to specify a program which should be run whenever a file or directory is accessed, opened for reads, opened for writes, written to, etc. Basically anything at the VFS level. :-)
Yeah, BeOS has that - it lets them do some really neat stuff. Unfortunately I can't deal with BeOS on a day-to-day basis without going insane, so I'd love to see Linux or FreeBSD support this.
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No, but it has had a logging option to mount since Solaris 7.
In the immortal words of Socrates, who said; 'I drank what?'
I think that's a little unfair. The comparison was between Tux2 and ext3, and if one is vapor then both are. They're at similar stages in development and their authors present similar pictures of their progress.
Please, please, please try to keep straight the differences between journaling and log-structured filesystems. There's enough confusion on this issue already, and FFS is not log-structured. AFAIK nothing being actively developed for Linux is log-structured.
I think you're right, though, about journaling vs. soft updates (of which I think Tux2's atomic update is a sub-category, though DP might disagree). Soft updates are more flexible than journaling, and - with a filesystem whose basic structures are designed to take advantage - perform better than journaling. I find it just slightly weird that there's so much focus on journaling when a superior alternative is known. I shouldn't bitch, though. For years certain people's ignorance, unwillingness to learn, and territoriality stood in the way of any progress in this area, and I for one am glad that the threat of competition has finally shaken their "hours-long fsck is OK for me" complacency. It would have been even nicer if they had responded by embracing the new entries instead of scrambling to maintain the incumbent's dominance by upgrading it just enough to stay competitive (does that remind anyone else of MS tactics?) but one can't make a purse out of a sow's ear.
Disclaimer: all views expressed are my own. If my employer took my views more seriously, their stock might not have tanked so badly.
Slashdot - News for Herds. Stuff that Splatters.
One concept I would love to see implemented is "watchdogs." This is the ability to specify a program which should be run whenever a file or directory is accessed, opened for reads, opened for writes, written to, etc. Basically anything at the VFS level. :-)
Logging is trivial to implement.
ACLs are trivial to implement. The program looks at the user and can indicate (via return code) whether to permit access.
Compression and encryption are relatively easy to implement, if you also retain some state information betweens calls.
Even virtual files and directories can be implemented. This could be used to implement things like "ftp" and "http" mounts.
There's a lot of similarities with "user space" file systems, and that concept might be preferred now.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
Fat/vfat file systems don't have the concept of an "owner," but NTFS does. Ideally this ownership information (and ACL permissions) will be retained even if someone sticks an NTFS-formatted zip disk into a Linux box.
The problem is that there's no obvious connection between NTFS ownerships and the user/group of the host Linux system. If you trust root to identify the mapping you leave the system open to attack by anyone with local root access. This would prevent Linux from being adopted in some environments.
A similar problem occurs with the network file systems. You want to avoid the biggest headache in NFS, the ability of someone with local root access to impersonate any other user. It's possible, but it requires the system distinguish between network and local user ids.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
The application (which includes the tools for manipulating ACLs) have to know what semantics are supported.
If there's a single VACL layer, any application that supports one underlying FS will support all.
If there's multiple ACL layers, then you'll need separate tools for each type of filesystem. This means you have to know what FS you're residing on. This is a Bad Thing (TM).
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
All existing applications will use the standard calls and either suceed or fail.
I think you're too quick to dismiss the idea of unified ACL tools, though. Could you imagine the chaos if the VFS didn't exist and you had to use "ls" on ext2, "dir" on dos/vfat/iso, "nls" on nfs, etc.? Can you imagine the pain of keeping track of which application works on each directory? Many people would prefer to see a minimal set of ACL semantics that work everywhere (if supported at all) than a more robust set that only works part of the time.
But the key point which I think you're missing is that you're thinking of ACLs as what lives on a Unix disk locally mounted. If you've mounted a NTFS partition, there is no "user/group" in the ACL, there's only a list of UUIDs. If you've mounted an AFS image, there's globally unique user-ids which may not correspond cleanly to your local users. (One thing everyone agrees on is that networked ACLs should not be vulnerable to the same trivial spoofing as NFS ownerships!)
Conceptually, all ACLs are doing the same thing so it should be possible to identify an abstraction. In practice, this hadn't been done at the time I last investigated the issue.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
The problem is that Unix filesystems only provide course control. ACLs provide much finer control.
An example of where ACLs would be required would be a well-run law or medical office. Each person would have their own user id, and would be in a couple groups. (Doctors, lawyers, secretaries, nurses, paralegals, etc., plus departmental groups.)
But confidentially still means that many files should be accessible only to a few people, e.g., one lawyer, one paralegal and one legal secretary. If someone goes on vacation, their replacement needs to have access during the period they're covering the regular person, but no longer. If someone else needs to be brought in for consultation, they might need read-only access for a while.
Try doing that with Unix permissions. It's possible, but it is *extremely* difficult and runs into combinatorical explosion with more than a handful of people. (Basically you need to create a "group" with every possible subset of users. You then change the group permissions to implement these semantics.)
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
I haven't been following the kernel discussion for some time, but I recall that there was some concern over how to handle ACLs.
The problem is that Linux supports a *lot* of different filesystems, and they often have different ACL semantics. (Think standard Unix ACLs, NT ACLs keyed by UUIDs, and network FS ACLs.) The way to implement any single set of semantics is obvious, but the way to implement a virtual ACL level so you can hide the details from applications is not.
Until this has been figured out -- or the cost of maintaining multiple ACL semantics outweighs the cost of not having ACL support -- all of the ACL patches will remain outside of the main kernel tree.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
Maybe it's my limited experience with ACLs, but while I can see why ACLs are an attractive feature, I've rarely found a situation where they can be used without making administration complex. Unix file permissions may be simple, but they are also dead easy to manage.
In Solaris, the OS uses standard Unix permissions, with the possibility of optionally using ACLs (I don't know about other Unices). This gives admins the options of using ACLs for a few limited cases - anything more, and it's probably better to setup a special Unix group of something.
Perhaps my problem is that my exposure to ACLs has been primarily with NT and that can be *very* difficult to manage.
Gee, thanks for wasting my time and yours.
I could name it for you -- "TrollFS"
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Napster-to-go says "Fill and refill your compatible MP3 player", which is a lie. It's not MP3. It's WMA with DRM.
I stand by my original post; there was no information in yours.
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Napster-to-go says "Fill and refill your compatible MP3 player", which is a lie. It's not MP3. It's WMA with DRM.
XPFS or CPFS
(cross platform FS)
Good suggestion! Thanks!
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Napster-to-go says "Fill and refill your compatible MP3 player", which is a lie. It's not MP3. It's WMA with DRM.
A few co-workers and myself are writing a new filesystem that includes ACL support. It's also journaled, 64-bit, supports named streams, and has indexed directories.
It emulates unix-type bitmask permissions with ACLs, and optimizes for the common cases. This means that chown, chmod, chgrp, etc. will all work unmodified.
We should be ready to do an initial beta release in one to two months for Linux 2.2.18. After that, we'll have ports for Windows 2000, FreeBSD and maybe Linux 2.4 -- depending on how stable its VFS, VM, etc. interfaces look at the time. We also plan SOlaris and HPUX ports.
An additional feature is that file system metadata is endianness-independant, so you can use the same filesystem with big or little-endian hardware. And it will be possible to pull a drive out of a Linux machine running this FS, mount it under Windows 2000, copy data back and forth, set ACLs, etc, then put it back in the Linux machine and keep on using it. Which will be sweet. Of course, it'll also mean that people who dual-boot with Linux and Win2k can have a common filesystem.
We've tentatively named the filesystem "CXFS" -- but we realize that SGI also has a "CXFS." What do you think would be a good (short, meaningful, catchy) name for an efficient cross-platform journaled filesystem?
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Napster-to-go says "Fill and refill your compatible MP3 player", which is a lie. It's not MP3. It's WMA with DRM.
Linux 2.4 w/ XFS really is a marvel. Even though its is supposedly beta quality, it has been rock solid for me (two weeks of benchmarking it against BFS ;) and there don't seem to be any real issues using it on Linux. You have to switch to LILO (remember that?) and you lose some as of yet unimplemented features (group quotas) but it is very solid. My benchmarks put the Linux version as faster than BFS and ReiserFS, and feature-wise it has attributes (too bad Linux won't take full advantage of them) and all the other feature seem to have made it to the Linux port unmolested.
A deep unwavering belief is a sure sign you're missing something...
I've been playing around with XFS for a few weeks, and I must say it kicks total ass. It's a good bit faster than ReiserFS and seems to have fewer problems with latencies. On the Bonnie benchmark (which are apparently biased according to some kernel developers) XFS get 3x the I/Os per second, and in real world cp and tar testing, it is noticably faster. That said, it seems to also have ACL support.
A deep unwavering belief is a sure sign you're missing something...
Eros has some great white papers
What is a Capability, Anyway?
Where Capabilities Come From
Comparing ACLs and Capabilities
Does anyone know what is keeping ACLs out of the kernel? Has Linus ever said where he stands on a standard ACL implementation for Linux?
/dev?
I asked Alan Cox about this and he said that capabilities were pretty much unrecognized by the wider comunity, and thus there were no need for ACLs. But IMHO, capabilties aren't nearly as clean as ACLs (rwxs + capabilities can be confusing, ACLS put everything neatly in one permission system).
There's a large portion of (well, dickheads, really) who think any idea implemented in NT doesn't belong in Linux. This ignored the fact that the Trusted flavors of various closed source Unixes and VMS have had the same system for years. And that Microsoft, whilst not having the worlds best business practices, can occassionally make good OS deesign decisions
(and even sometimes be the best tool for the job, but that's OT).
I'm not sure what Linus would say, but I'd like to echo those sentiments exactly. There's no reason I, nor any service, ever need to run as root.
* Why does my mail server need a small program with permissions to install a rootkit in
* Why can't I delegate the task of adding and deleting users to a minion without worrying they will corrupt the filesystem?
* When I want full access to a file, managers to have read and execute access, employees to have read access, and nobody else to have any access at all, why can't I just DO IT?
Rwxs wasn't designed for security. ACLs even fit in better with the Unix philosophy of giving users and processes only the permissions they need to use the system and no more.
Sudo is a hack.
Use the SMB PAM module with Apache to authenticate form the NT server
Use Halycon Software of Chilisoft to deploy your ASP app on Linux.
Does anyone know what is keeping ACLs out of the kernel? Has Linus ever said where he stands on a standard ACL implementation for Linux?
/dev? Why can't I delegate the task of adding and deleting users to a minion without worrying they will corrupt the filesystem.
I asked Alan Cox about this and he said thatcapabilities were pretty much unrecognized by the wider comunity. But IMHO, cpaabilties aren't nearly as clean as ACLs.
There's a large portion of (well, dickheads, really) who think any idea implemented in NT doesn't belong in Linux. This ignored the fac that the Trusted flavos of varios closed source Unixes and VMS have had the same system for years. And that Microsoft, while not having the worlds best business practices, can occassionally make goodOS deesign decisions, and even sometimes be the best tool for the job.
I'm not sure what Linux would say, but I'd like to echo those sentiments exactly. There's no reason I, not and service, ever neeed to run as root. Why does my mail server need a small program with permissions to install a rootkit in
Sudo is a hack.
I felt obliged to point out that Daniel Phillips, of the Tux2 file system, has now created indexed searched through directories (similar conceptually to btrees, but not quite as fast).
Check out the mailing list archives here
For directories with over 20000 files, the results are 10 times faster with the indexed searching. The ratio gets better with more than that. So I guess ext2 won't have to wait long for btrees. If Tux2 happens sometime soon then it will really rock ! Great job Daniel !
I think that's a little unfair. The comparison was between Tux2 and ext3, and if one is vapor then both are. They're at similar stages in development and their authors present similar pictures of their progress.
Except that you can download working ext3 code, and have been able to for more than a year. As of yet Tux2 is still design plans, without any public working implementation.
Tux2 has a much more interesting technology
Tux2 is still vaporware. I agree, it will be great when it comes out. However, it is currently vaporware.
ReiserFS and XFS are also really great,
So these have log structure (or btree) and journalling. However, ReiserFS is broken with NFS currently, and that is a BIG problem. XFS is still beta and not merged with the main kernel tree, which is also a BIG problem. Ever see the fallout when Alexander Viro (kernel VFS hacker) takes a newly merged filesystem to task ?? It is not pretty.
Ext3 has some advantages. It has been running stably for a long time now under development. It is journaled, and has a small code base. It also only exists for the 2.2 kernel series.
Phillips is also making a judgment call. He wants to build on ext2 with tux2. Ext2 is not log structured, which is why ReiserFS can beat it in well-structure benchmark tests run by Hans.
The future, IMHO, is a log structured file system with NO journaling and atomic updates. This creature already exists, and it is called FFS with Soft Updates, from the FreeBSD developers. Here is the breakdown.
Journalling is tricky, as it requires lots of intervention at other places in the kernel. You need to keep something synchronous - journalling just makes that something very small. Atomic updates avoid synchronous issues altogether. Instead, they structure the file system in groups of data and metadata. In each group, there is an atomic bit. When set, it means the group is intact. So, upon looking through the groups, you can immediately determine which ones are intact and which are incomplete. Recovery is REALLY fast after a power outage, in theory even faster than a journal recovery.
WRT log structuring and btrees, these allow small and large files to live together easily, and allow rapid searches in large directories. Both of these have substantial advantages.
And the future for linux file systems ?? I don't know, it is always interesting to see where things will head. The world is clamoring for easy crash recovery, and ext2's days are numbered. I think most people would be quite happy to simply add journaling to ext2. Or atomic updates. So I predict, after consulting the crystal ball, that tux2 develops a large following after release, and that Phillips then adds btree searches and log structuring, making it the first linux file system with all that.
That would then bring the state of the art file systems for linux up to par with those of FreeBSD. Of course, in linux at that time you can also use JFS, XFS, ReiserFS, or ext3 journaled file systems.
But journaling is worse than atomic updates, both for complexity and speed.
I'd presume he means that you can't export a ReiserFS filesystem as an NFS share.
Vintage computer games and RPG books available. Email me if you're interested.
Vintage computer games and RPG books available. Email me if you're interested.
Vintage computer games and RPG books available. Email me if you're interested.
Okay, I know it's a bit off the topic of Linux and all, but isn't TrustedBSD working in ACL's into FreeBSD 5.0? I need to go back and read that interview again.
For myself, I know that ACL's are the #1 reason why my primary file server at work is still an NT. Maybe I just don't fully grasp all the ways you can tweak *nix file permissions. I just don't see how you can assign one group ownership rights, one group read/write, and yet another group read only while not allowing "everyone" any kind of access. How about allowing a group of folks the right to write to a file, but not delete it?
I do prefer FreeBSD for specific server tasks. Web serving is certainly the top of that list. Thing is, without the granularity of ACL's I can't leave NTFS behind when it comes to the more complex task of file sharing to a bunch of users on a LAN.
Additionally, I've gotten quite used to the notion of leaving the OS permissions to Everyone on my files on the server, then restrict access via the share permissions. The server itself is physically locked in a room so I'm not normally concerned with local security. As cool as Samba is, it makes no provisions for implementing permissions of any sort. Heck, for 95% of my ACL needs, they could be implemented in Samba and never touch the FS.
The line must be drawn here. This far. No further.
Does anyone know what is keeping ACLs out of the kernel? Has Linus ever said where he stands on a standard ACL implementation for Linux?
(I hate it when that happens. I put in everything but the conclusion.)
IMHO, access lists are only useful to allow you to fill in the little checkbox on government/military procurement forms "access lists? (y/n)" with a "y"
Only way you're gonna get Linux into government/military stuff is to have access lists. Full stop. Therefore, ACLs are very useful (vital, actually) as a patch to some standard filesystem, just so you can check the little box. As to merging them into the kernel, forget it. They really accomplish nothing, and just get in the way.
--
Welcome to the Turing Tarpit, where everything is possible but nothing interesting is easy.
They should put in 2 new moderation categories - wrong and didn't read the damn thing. You'd fall into the latter. Read the one above mine, then read mine again. Perhaps I did make an error, but I don't think so...
ALL YOUR BASE ARE BELONG TO US!
SIG: HUP
See, and that's at the heart of the design issue. Many of the "limited" permissions you might construct with ACLs turn out to be equivalent to "root" permissions anyway; having ACLs gives you a false sense of security. Delegation of specific privileges generally only works reliably with very careful programmatic permission checking. That's why UNIX has setuid programs.
ACLs allow users to come up with quick workarounds to access control problems. It's easy for the administrator in the short run because people won't bother you about this or that. But you end up with an incomprehensible mess of access rights, and you end up with lots of questions of why something does or does not work.
The traditional UNIX system, instead, forces people to think ahead and define clearly what they are trying to accomplish. Then they define a group for that purpose. The end result is easier to understand and easier to analyze.
On balance, I'd rather not have ACLs. There is value in keeping things simple.
There are *such* better projects than ext3 that are so much further along its rediculous to think that ext3 has any chance of becomming the next standard filesystem. Tux2 has a much more interesting technology that could allow really great stuff, such as journaling of meta and file data. It'll even be possible to use its phase tree algorithm to allow online fscks (useful to check for decaying filesystems). ReiserFS and XFS are also really great, but Tux2 and ext3 are the only ones that can convert ext2 automatically. Daniel Phillips who's working on Tux2 is also pumping all sorts of other nifty features into the patch, such as tail merging and a system that puts btree efficiency into the FS without the complexity of btrees. Its way beyond the competition. Further, it should be ready for the 2.5 tree, while ext3 has been in development for 2 years...