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    SubjectRe: Upstream first policy

    On Mon, 8 Mar 2010, Rik van Riel wrote:
    > On the other hand, '/etc/shadow' has the opposite constraint,
    > where the system will not trust most of the applications with
    > the data from that file.

    Umm. No.

    /etc/shadow is in no way at all different from /etc/passwd. Both of them
    have pathname-based security issues. The fact that both of them _also_
    have content-based security issues is an independent issue that I just
    assumed everybody would take for granted.

    Clearly I assumed too much.

    So I was assuming that everybody realized that the normal inode-based UNIX
    security obviously means that you can only open /etc/passwd read-only as
    any normal user (and not open /etc/shadow at all: but that is in _no_ way
    different from /etc/passwd).

    That's an example of non-pathname-based security, where you actually mark
    the content itself restricted some way. It's very naturally done with
    labels on the inode itself. It's what UNIX has _always_ done

    Nobody has ever suggested removing that. That would be crazy.

    But that thing is _independent_ from the other totally unrelated issue,
    namely the fact that "/etc/passwd" is a special name in the namespace. In
    other words, there is "content security", but then there is also
    "namespace security".

    Of course, you can make /etc unwritable, and that is indeed the
    traditional UNIX model of handling namespace security: by just
    implementing it as "content security" of the directory.

    The sgid and sticky bits can be used to further try to make it more
    fine-grained (exactly becuase it is _not_ sufficient to say "you can't
    read or write this directory" on a whole-directory basis), and obviously
    SELinux has extensions of its own too.

    Can you really not see the difference between security of naming thigns
    certain things (like "/etc/passwd") - pathname based issues - and the
    separate security of limiting access to any named device - actual markings
    on the inode itself?


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