Re: new ...at() flag: AT_NO_JUMPS

[Andy Lutomirski]

On Sat, Apr 29, 2017 at 3:04 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> New AT_... flag - AT_NO_JUMPS
>
> Semantics: pathname resolution must not involve
>         * traversals of absolute symlinks
>         * traversals of procfs-style symlinks
>         * traversals of mountpoints (including bindings, referrals, etc.)
>         * traversal of .. in the starting point of pathname resolution.

Can you clarify this last one?  I assume that ".." will be rejected,
but what about "a/../.."?  How about "b" if b is a symlink to ".."?
How about "a/b" if a is a directory and b is a symlink to "../.."?

> Right now I have it hooked only for fstatat() and friends; it could be
> easily extended to any ...at() syscalls.  Objections?

I like it, assuming the answers to all the questions above are that
they will be rejected.