linux-kernel - Re: [PATCH 2/4] Expose O

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Date:   Tue, 12 Feb 2019 13:18:10 -0700
From:   Andreas Dilger <adilger@...ger.ca>
To:     demiobenour@...il.com
Cc:     Jeff Layton <jlayton@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH 2/4] Expose O_PATHSTATIC to userspace

On Feb 12, 2019, at 7:54 AM, demiobenour@...il.com wrote:
> 
> From: "Demi M. Obenour" <demiobenour@...il.com>
> 
> This adds the file open flag O_PATHSTATIC, which ensures that symbolic
> links are *never* followed, even in path components other than the last.
> This is distinct from O_NOFOLLOW, which only prevents symlinks in the
> *last* component from being followed.
> 
> This is useful for avoiding race conditions in userspace code that
> should expose only a subset of the filesystem to clients.  This includes
> FTP and SFTP servers, QEMU, and others.
> 
> Currently, O_NOFOLLOW must be set if O_PATHSTATIC is set.  Otherwise,
> open() fails with -EINVAL.

I don't want to bikeshed (discard suggestion if you disagree), but why not
name the flag "O_NEVER_FOLLOW" so that users can see it is also related to
"O_NOFOLLOW"?  Otherwise it seems like they are two completely different
things from looking at the names, when in fact they are closely related.

Cheers, Andreas






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