linux-kernel - Re: Have RESOLVE_* flags superseded AT

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Message-ID: <20200302143546.srzk3rnh4o6s76a7@wittgenstein>
Date:   Mon, 2 Mar 2020 15:35:46 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Florian Weimer <fweimer@...hat.com>, linux-api@...r.kernel.org,
        viro@...iv.linux.org.uk, metze@...ba.org,
        torvalds@...ux-foundation.org, cyphar@...har.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Have RESOLVE_* flags superseded AT_* flags for new syscalls?

On Mon, Mar 02, 2020 at 02:27:08PM +0000, David Howells wrote:
> Christian Brauner <christian.brauner@...ntu.com> wrote:
> 
> > > AT_SYMLINK_NOFOLLOW only applies to the last pathname component anyway,
> > > so it's relatively little protection.
> > 
> > So this is partially why I think it's at least worth considerings: the
> > new RESOLVE_NO_SYMLINKS flag does block all symlink resolution, not just
> > for the last component in contrast to AT_SYMLINK_NOFOLLOW. This is
> > 278121417a72d87fb29dd8c48801f80821e8f75a
> 
> That sounds like a potentially significant UAPI change.  What will that break?

I think we settled this and can agree on RESOLVE_NO_SYMLINKS being the
right thing to do, i.e. not resolving symlinks will stay opt-in.
Or is your worry even with the current semantics of openat2()? I don't
see the issue since O_NOFOLLOW still works with openat2().

Christian