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    SubjectRe: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering
    On Wed, 25 May 2011 11:42:44 -0700, Linus Torvalds <> wrote:
    > On Wed, May 25, 2011 at 11:01 AM, Kees Cook <> wrote:
    > >
    > > Can we just go back to the original spec? A lot of people were excited
    > > about the prctl() API as done in Will's earlier patchset, we don't lose the
    > > extremely useful "enable_on_exec" feature, and we can get away from all
    > > this disagreement.
    > .. and quite frankly, I'm not even convinced about the original simpler spec.
    > Security is a morass. People come up with cool ideas every day, and
    > nobody actually uses them - or if they use them, they are just a
    > maintenance nightmare.
    > Quite frankly, limiting pathname access by some prefix is "cool", but
    > it's basically useless.
    > That's not where security problems are.
    > Security problems are in the odd corners - ioctl's, /proc files,
    > random small interfaces that aren't just about file access.
    > And who would *use* this thing in real life? Nobody. In order to sell
    > me on a new security interface, give me a real actual use case that is
    > security-conscious and relevant to real users.
    > For things like web servers that actually want to limit filename
    > lookup, we'd be <i>much</i> better off with a few new flags to
    > pathname lookup that say "don't follow symlinks" and "don't follow
    > '..'". Things like that can actually be beneficial to
    > security-conscious programming, with very little overhead. Some of
    > those things currently look up pathnames one component at a time,
    > because they can't afford to not do so. That's a *much* better model
    > for the whole "only limit to this subtree" case that was quoted
    > sometime early in this thread.

    The "make sure we don't follow symlinks at all" is a real problem in
    VirtFS ( that we are fixing
    by adding a forked chrooted process to Qemu. If we are open to a new
    open flag O_NOFOLLOW_PATH, which would fail with ELOOP if any of the
    path component is a symbolic link, that would greatly simplify VirtFS.
    Will such a new flag to open be acceptable ?


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