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    SubjectRe: symlinks with permissions

    > >> It looks to me like it has been this way for better than a decade
    > >> without problems so there is no point in changing it now.
    > >
    > > Unix compatibility?
    > Thinking about this proc fundamentally gives you the ability to create
    > (via open) a new file descriptor for a file you already have open.

    Yes. Problem is that by using /proc, I can work-around open(READONLY)
    restriction and work-around open(APPEND_ONLY) restriction.

    > I do see a security issue in your example, but the security issue I
    > see is how you have chosen to use the linux facilities, that have been
    > there for ages. Facilities cloned from plan 9 and apparently
    > available in slightly different forms on many unix variants existence.
    > /dev/fd/N is not a linuxism.
    > To close this whole would require some sort of stacking inode that
    > when opened opened the real fs inode. With all kinds of convolutions
    > and complications. Just to close the issue that some idiot might
    > give someone a fd to a world writeable file that they don't want
    > them to open.

    Ok, so you agree issue is there. Good.

    Now, fix for READONLY issue should be fairly simple: follow link in
    /proc/*/fd/* should check the link permissions, and return
    read-only/write-only descriptors as neccessary.

    Basically, that follow link should behave as dup(), not as open().

    > I certainly am not interested in debugging or maintaining the stacking
    > inode code that would be necessary to close this theoretical corner
    > case. There are much more real bugs that need attention.

    But if we can get trivial 10-liner, that should be acceptable, right?

    (cesky, pictures)

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