Date: Fri, 12 Jul 2019 20:12:07 +0200 From: Steffen Nurpmeso <steffen@...oden.eu> To: oss-security@...ts.openwall.com Subject: Re: Privileged File Access from Desktop Applications Perry E. Metzger wrote in <20190712121202.403b2f5f@...berwock.cb.piermon\ t.com>: |On Fri, 12 Jul 2019 11:53:26 -0400 "Perry E. Metzger" |<perry@...rmont.com> wrote: |>>> What's the right way to handle this stuff? Capabilities, |>>> probably. It's what they're designed for. |>> |>> They're completely not designed for this case. Setting |>> CAP_DAC_OVERRIDE or CAP_SYS_ADMIN is very close to SUID root. See: |>> https://grsecurity.net/false_boundaries_and_arbitrary_code_execution.php |> |> Those aren't capabilities. Those are this POSIX mechanism that got |> the same name for no good reason and doesn't do anything like what |> an actual capability system does. | |It occurs to me that people without a background in computer security |might not know what a capability actually is, or how a capability |based security system manages access control. Some people are too lazy to switch to a different graphical console or terminal, or are settled on using their very own graphical editor in the very current graphical session, instead of indirecting through sshfs or simply doing a ssh to root in some graphical console on the current box, and edit through that. I personally have a TLS setup and a SSH setup and a PGP (GnuPG actually) setup, and there is a PAM setup here with passwords not some (Yubi)key, and i also have some encfs which could make many of you shiver (since it is not the block level GELI i think or dmcrypt/LUKS on Linux), that makes five things to care about, and five things people have to audit and often do not, even though many are talking, with best intentions. I do not have dbus running except when firefox is started (which hangs often for scripts sourced from derstandard.at especially when opening several tabs there, looking at images, whatever, twice yesterday and i am not sooo active, so that is on the bus), which i have a special account for. (Two, in fact.) The Tso of Linux once told how he performs a git commit to the Linux kernel, and it was about plugging in some keycard into some cardreader in order to sign. If you pass a border or in police control you have to show your passport. If i want to edit a system configuration file i have to type the root password (no XKey here still), either for sudo/super/doas/su or login. If a younger person thinks this sucks i understand in parts, but i am almost certain he is the one who screams for security when something bad happens and takes away the toy. No to webmin, no to admin://, no to sending mails from within TheGimp, that all can be done in a better way from within emacs. Hasta la victoria siempre. Some things just don't work out. |This Wikipedia page: |https://en.wikipedia.org/wiki/Capability-based_security |isn't the best, but it does have good pointers to real explanations. | |For a look at how you can implement a capability system on top |of Unix, see Capsicum, which was built for FreeBSD but never actually |ported to Linux (which is sad and should be corrected): |https://www.cl.cam.ac.uk/research/security/capsicum/papers/2010usenix-se\ |curity-capsicum-website.pdf | |Note that a primitive form of capabilities can be achieved in the |current Linux kernel by passing file descriptors between processes, a |tool relatively few people seem to know exists. Given that the |"correct" mechanism (something like Capsicum) doesn't exist in Linux |yet, it's a poor man's second best. Again, porting Capsicum would be |the smart thing to do instead of all this ad hoc stuff. It is painful programming. Now there is Casper (not Kasper) which improves this a bit, i think. And well it cannot be helped. Model View Controller for anything, or at least Frontend and Machine like Mr. Pike did the first time for Sam as far as i know, almost fourty years ago, that is what i am going for myself. Much of it is about hardware too, i am in video and audio and kvm groups, and this matters down to the hardware, which is not compartmentalised on rather cheap consumer level as far as i know. --steffen | |Der Kragenbaer, The moon bear, |der holt sich munter he cheerfully and one by one |einen nach dem anderen runter wa.ks himself off |(By Robert Gernhardt)
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