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From:   Andreas Dilger <adilger@dilger.ca>
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Subject: Re: [PATCH 2/4] Expose O_PATHSTATIC to userspace
Date:   Tue, 12 Feb 2019 13:18:10 -0700
In-Reply-To: <20190212145450.2200-2-demiobenour@gmail.com>
Cc:     Jeff Layton <jlayton@kernel.org>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        linux-arch@vger.kernel.org
To:     demiobenour@gmail.com
References: <20190212145450.2200-1-demiobenour@gmail.com>
 <20190212145450.2200-2-demiobenour@gmail.com>
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On Feb 12, 2019, at 7:54 AM, demiobenour@gmail.com wrote:
> 
> From: "Demi M. Obenour" <demiobenour@gmail.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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