Re: [PATCH 1/3] fs: add O_BENEATH flag to openat(2)

[Al Viro]

On Mon, Nov 03, 2014 at 11:48:23AM +0000, David Drysdale wrote:
> Add a new O_BENEATH flag for openat(2) which restricts the
> provided path, rejecting (with -EACCES) paths that are not beneath
> the provided dfd.  In particular, reject:
>  - paths that contain .. components
>  - paths that begin with /
>  - symlinks that have paths as above.

Yecch...  The degree of usefulness aside (and I'm not convinced that it
is non-zero), WTF pass one bit out of nameidata->flags in a separate argument?
Through the mutual recursion, no less...  And then you are not even attempting
to detect symlinks that are not followed by interpretation of _any_ pathname.
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