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Date:   Sat, 16 May 2020 21:47:38 -0700 (PDT)
From:   Christian Kujau <lists@nerdbynature.de>
To:     Patrick Donnelly <batrick@batbytes.com>
cc:     Al Viro <viro@zeniv.linux.org.uk>,
        open list <linux-kernel@vger.kernel.org>,
        Jeff Layton <jlayton@redhat.com>, xiubli@redhat.com,
        kchai@redhat.com
Subject: Re: file system permissions regression affecting root
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On Wed, 13 May 2020, Patrick Donnelly wrote:
> However, it seems odd that this depends on the owner of the directory.
> i.e. this protection only seems to be enforced if the sticky directory
> is owned by root. That's expected?

According to the documentation[0] this appears to be intentional:

 protected_regular:
   [...]
   When set to "1" don't allow O_CREAT open on regular files that we
   don't own in world writable sticky directories, unless they are
   owned by the owner of the directory.

C.

[0] https://www.kernel.org/doc/Documentation/sysctl/fs.txt
-- 
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It's stuck in the Web.