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RichFelker's profile
Rich Felker
Rich Felker
Rich Felker
@RichFelker

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Rich Felker

@RichFelker

Yeah, I do @musllibc, FOSS & infosec stuff. But now is not the time for a mostly-/only-tech Twitter feed.

musl-libc.org
Joined March 2014

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    1. Bryan Steele‏ @canadianbryan Aug 29

      Bryan Steele Retweeted majek04

      Ya'll need to discover pledge(2), unveil(2) and privilege separation. ☺️https://twitter.com/majek04/status/1034759172041129984 …

      Bryan Steele added,

      majek04 @majek04
      One of the worst API's out there - linux capabilities. http://man7.org/linux/man-pages/man7/capabilities.7.html … API is technically good, but impossible to use in practice. Inheriting caps is basically impossible: - you need either ambient cap - or a cap in I+P set, and permissions on execed file
      Show this thread
      3 replies 1 retweet 18 likes
      Rich Felker‏ @RichFelker Aug 29
      Replying to @canadianbryan

      Linux capabilities are awful and blaming that shit on POSIX by calling them "POSIX capabilities" when they have nothing to do with POSIX is.... uhg.

      6:42 AM - 29 Aug 2018
      • 3 Retweets
      • 7 Likes
      • グレェ「grey」 Philip Hofer Michał K. Feiler (ArchieT) Laurent Bercot Aslak Raanes Will Orr Bryan Steele Jason Bucata - Tech
      3 replies 3 retweets 7 likes
        1. New conversation
        2. Rich Felker‏ @RichFelker Aug 29
          Replying to @RichFelker @canadianbryan

          Linux has seccomp something like the pledge model, but sadly it doesn't work well when you don't control the whole implementation stack.

          1 reply 1 retweet 1 like
        3. Bryan Steele‏ @canadianbryan Aug 29
          Replying to @RichFelker

          Yeah, doesn't really support the incremental dropping mechanics either, just a single policy to rule them all, nothing preventing going to other way either.

          1 reply 0 retweets 2 likes
        4. Rich Felker‏ @RichFelker Aug 29
          Replying to @canadianbryan

          All aspects of a good privilege model should be incremental and irreversible drop. (No suid or setcap, etc.) With that you can make chroot, all namespace type operations unprivileged and safe.

          0 replies 3 retweets 5 likes
        5. End of conversation
        1. New conversation
        2. rt2800pci1‏ @rt2800pci1 Sep 5
          Replying to @RichFelker @canadianbryan

          How do you feel about capabilities attached to file descriptors, like Capsicum in FreeBSD does?

          2 replies 0 retweets 0 likes
        3. Rich Felker‏ @RichFelker Sep 5
          Replying to @rt2800pci1 @canadianbryan

          Bad. Privs should be drop-only, no way to add once dropped.

          3 replies 0 retweets 0 likes
        4. rt2800pci1‏ @rt2800pci1 Sep 5
          Replying to @RichFelker @canadianbryan

          I am not particularly experienced in this area, so I'd like to learn why would it be bad. An eg, the parent process passes a R/W fd to only the files the child needs to write to, and then make everything else R/O.

          1 reply 0 retweets 1 like
        5. rt2800pci1‏ @rt2800pci1 Sep 5
          Replying to @rt2800pci1 @RichFelker @canadianbryan

          It would also be nice if you can point me at some doco on this stuff, most of what I read is system specific hence a bit opinionated (Linux people think seccomp is better, OpenBSD people would say pledge/unveil is, I hope you get my point :))

          1 reply 0 retweets 0 likes
        6. Ed Maste‏ @ed_maste Sep 5
          Replying to @rt2800pci1 @RichFelker @canadianbryan

          Capability Myths Demolished http://srl.cs.jhu.edu/pubs/SRL2003-02.pdf … is pretty good at explaining capability systems; it predates Capsicum and doesn't directly apply to the capability-as-fd hybrid model but gives a good overview of the concepts

          2 replies 0 retweets 2 likes
        7. Bryan Steele‏ @canadianbryan Sep 6
          Replying to @ed_maste @rt2800pci1 @RichFelker

          Capsicum is like snakeoil, a name drop into conversations about security. With very few practical applications fully taking advantage of its "capabilities". And the ones in the past that perhaps did, *cough* (where's chrome?) are vapourware & not maintained. Sorry, not buying it.

          1 reply 0 retweets 1 like
        8. Bryan Steele‏ @canadianbryan Sep 6
          Replying to @canadianbryan @ed_maste and

          Chrome pledges by default today, and has for some time. unveil(2) is also ready for testing and can be easily enabled. Capsicum patches never made it into FreeBSD ports. The examples elsewhere basically fiddle with a few descriptors, not clear how they're making things "secure".

          2 replies 1 retweet 1 like
        9. Bryan Steele‏ @canadianbryan Sep 6
          Replying to @canadianbryan @ed_maste and

          Compare: https://github.com/openssh/openssh-portable/blob/master/sandbox-capsicum.c … To: https://github.com/openssh/openssh-portable/blob/master/sandbox-seccomp-filter.c … https://github.com/openssh/openssh-portable/blob/master/sandbox-darwin.c …https://github.com/openssh/openssh-portable/blob/master/sandbox-pledge.c …

          1 reply 0 retweets 1 like
        10. 4 more replies
        1. New conversation
        2. Rich Felker‏ @RichFelker Aug 29
          Replying to @RichFelker @canadianbryan

          Someone correct me if I'm wrong, but I think what happened was this: POSIX realized root was stupid, and switched to making "appropriate privileges" implementation-defined. Linux geeks somehow misread that as POSIX adopting their (copied from somewhere?) capabilities model.

          2 replies 0 retweets 1 like
        3. Rich Felker‏ @RichFelker Aug 29
          Replying to @RichFelker @canadianbryan

          There's some text in the Rationale document on it: http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xbd_chap03.html#tag_21_03_00_01 …

          0 replies 0 retweets 0 likes
        4. End of conversation

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