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Unix file access rwx permissions are simple but tricky

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Re: Unix file access rwx permissions are simple but tricky

#11

Post by DSMan195276 »

saulpw wrote: post #2

I've been wondering about this for awhile. Do we really need multiple users for desktop unix? I get that you want some division between system and user, to protect the user against themselves. And read-only files are similarly useful, if only because some devices are read-only. But do we really need user/group/other permissions for desktop unix? and all the complexity of groups, and euid, etc. Edit: not sure why I'm…

Users are still useful for isolation, many daemons on your system are likely running with different UIDs (or could be configured to do so) to increase isolation between them and the rest of the system.

Groups are a bit less useful (IMO), but still good for handing out access to things like device files. If a daemon should have permissions to XYZ /dev file then you add them to the group associated with it.

Re: Unix file access rwx permissions are simple but tricky

#12

Post by arp242 »

saulpw wrote: post #2

I've been wondering about this for awhile. Do we really need multiple users for desktop unix? I get that you want some division between system and user, to protect the user against themselves. And read-only files are similarly useful, if only because some devices are read-only. But do we really need user/group/other permissions for desktop unix? and all the complexity of groups, and euid, etc. Edit: not sure why I'm…

It seems to me that stuff like iwd, ntpd, udevd, bluetoothd, dhcpcd, etc. etc. each running as a different user is pretty desirable. Every system works like this, including Windows.

The most obvious reason for this is so that a security problem in one of these daemons won't be able to read your Firefox cookies, install a rootkit, and stuff like that.

Re: Unix file access rwx permissions are simple but tricky

#13

Post by throwaway87483 »

bloqs wrote: post #9
eadmund wrote: post #3

Earlier quoted context omitted.

Those multiple users could be used to implement sandboxing. And of course if one has a family then one might want accounts for Mom, Dad, Alice and Bob.

Depressingly i think sharing computers at least in the western world has become a thing of the past. At the very least, sharing your main form of computing.

We're sharing a computer as we speak.

Re: Unix file access rwx permissions are simple but tricky

#14

Post by stefan_ »

saulpw wrote: post #2

I've been wondering about this for awhile. Do we really need multiple users for desktop unix? I get that you want some division between system and user, to protect the user against themselves. And read-only files are similarly useful, if only because some devices are read-only. But do we really need user/group/other permissions for desktop unix? and all the complexity of groups, and euid, etc. Edit: not sure why I'm…

No, a group called "wheel", "dialout" and users "irc games uucp list gnats mail news" are essential to the Linux desktop. The only cruft facing the Linux desktop today is the unification of bin and sbin.

Re: Unix file access rwx permissions are simple but tricky

#15

Post by stefan_ »

ratorx wrote: post #6
saulpw wrote: post #2

I've been wondering about this for awhile. Do we really need multiple users for desktop unix? I get that you want some division between system and user, to protect the user against themselves. And read-only files are similarly useful, if only because some devices are read-only. But do we really need user/group/other permissions for desktop unix? and all the complexity of groups, and euid, etc. Edit: not sure why I'm…

User is useful for isolation, not just between system and user, but also between different bits of the system. This is more useful on a server running multiple different services, but desktop software often has multiple services as well (although I can’t think of an example right now). Groups are a bit more niche IMO, but without groups there is no real other way to express the constraint of thing X uses file A,B, th…

Except they all already use the insanity that is SELinux because they found users and groups too limiting for their "guaranteed to break production at runtime" security scheme. People suggesting we need user accounts for isolation are a generation behind the engineers tasked with papering over security issues.

Re: Unix file access rwx permissions are simple but tricky

#16

Post by ratorx »

stefan_ wrote: post #15
ratorx wrote: post #6

Earlier quoted context omitted.

User is useful for isolation, not just between system and user, but also between different bits of the system. This is more useful on a server running multiple different services, but desktop software often has multiple services as well (although I can’t think of an example right now). Groups are a bit more niche IMO, but without groups there is no real other way to express the constraint of thing X uses file A,B, th…

Except they all already use the insanity that is SELinux because they found users and groups too limiting for their "guaranteed to break production at runtime" security scheme. People suggesting we need user accounts for isolation are a generation behind the engineers tasked with papering over security issues.

SELinux is definitely over-engineered, but it’s not for the same problem as file permissions. File permissions are purely for files, whereas increasingly Linux does not nicely follow the philosophy of everything being a file. Once you have non-file resources and capabilities, it is very tempting to attempt to generalise permissions beyond them and if you attempt to bolt it on, you’ll get something like SELinux.

I wouldn’t say file permissions are necessarily outdated. You can get pretty far using something like systemd capabilities, which are much more supplementary to the existing Unix file permission model.

The very best approach to this IMO is OpenBSD pledge and unveil. Managing the permissions as part of the binary itself is much less fragile, although it doesn’t have exactly the same threat model. It also has the added benefit of temporal safety, which I’m not sure you can do with SELinux.

Re: Unix file access rwx permissions are simple but tricky

#17

Post by xcdzvyn »

throwaway87483 wrote: post #13
bloqs wrote: post #9

Earlier quoted context omitted.

Depressingly i think sharing computers at least in the western world has become a thing of the past. At the very least, sharing your main form of computing.

We're sharing a computer as we speak.

[dead]

Re: Unix file access rwx permissions are simple but tricky

#18

Post by teo_zero »

It's counterintuitive that the owner can have less rights than the others. Honestly, I've never seen it put in practice in any real-world file system.

Incidentally, this is also not very efficient: UNIX permissions as they are today require 9 bits, namely rwx for owner, rwx for group, and rwx for others. But in an alternative universe where owner's rights win over group's rights which win over others' rights, permissions could be coded in just 6 bits: 2 to express who can read, 2 for who can write, and 2 for who can execute. Each set of 2 bits would be interpreted this way: 00=nobody, 01=only owner, 10=group or owner, 11=everybody.

Re: Unix file access rwx permissions are simple but tricky

#19

Post by jesprenj »

0cf8612b2e1e wrote: post #10
saulpw wrote: post #2

I've been wondering about this for awhile. Do we really need multiple users for desktop unix? I get that you want some division between system and user, to protect the user against themselves. And read-only files are similarly useful, if only because some devices are read-only. But do we really need user/group/other permissions for desktop unix? and all the complexity of groups, and euid, etc. Edit: not sure why I'm…

It took me a shockingly long amount of time before I realized it was silly to have a username on my machines. I am the only person using this, why am I typing unnecessary cruft? Username switched to “a”, which ends up saving space in my home path and terminals.

It took me a shockingly long amount of time before I realized it was silly to have a username on my machines. I am the only person using this, why am I typing unnecessary cruft? Username switched to “root” on all my machines and I remove the username from PS1. /root is shorter than /home/a (:

Re: Unix file access rwx permissions are simple but tricky

#20

Post by pdonis »

saulpw wrote: post #2

I've been wondering about this for awhile. Do we really need multiple users for desktop unix? I get that you want some division between system and user, to protect the user against themselves. And read-only files are similarly useful, if only because some devices are read-only. But do we really need user/group/other permissions for desktop unix? and all the complexity of groups, and euid, etc. Edit: not sure why I'm…

> I get that you want some division between system and user

Which, as others have pointed out, means various system services running as other users (since you don't want them running as your user, and you also don't want them running as root). On most desktop unix machines that only one person uses, that's the main use case for multiple users (and for multiple groups since groups are used to manage access to various functions like printing, usb sticks, cd-roms, etc.).

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