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    SubjectRe: sys_chroot+sys_fchdir Fix
    On Wed, Sep 26, 2007 at 08:04:14PM +0930, David Newall wrote:
    > Al Viro wrote:
    > >Oh, for fsck sake... Folks, it's standard-required behaviour. Ability
    > >to chroot() implies the ability to break out of it. Could we please
    > >add that (along with reference to SuS) to l-k FAQ and be done with that
    > >nonsense?
    > I'm pretty confident that it's only standard behavior for Linux. Every
    > other unix says it's not allowed.

    OK, the possibilities are
    * you've discovered a bug in all Unices (BTW, even FreeBSD *does*
    allow to break out of some chroots in that fashion; RTFS and you'll see -
    just pay attention to setting fdp->fd_jdir logics in kern/vfs_syscalls.c:
    change_root(); it sets jail boundary on _first_ chroot and if you've got
    nested chroots, you can leave them just fine by use of SCM_RIGHTS to hold
    directory descriptor). All hail David, nevermind that this behaviour had
    been described in Unix FAQs since _way_ back.
    * you've misunderstood the purpose of chroot(), the fact that
    behaviour in question is at the very least extremely common on Unix and
    the fact that any code relying on root-proof chroot(2) is broken and needs
    to be fixed, simply because chroot is _not_ root-proof on (at least) almost
    all systems.

    Note that the last statement applies in both cases; it's simply reality.
    Insisting that behaviour known for decades is a bug since it contradicts
    your rather convoluted reading of the standards... Looks rather silly,
    IMO, but that has zero practical consequences anyway. Userland code can't
    rely on root-proof chroot(2), period.
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      Last update: 2007-09-26 20:43    [W:0.021 / U:8.212 seconds]
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