linux-kernel - Re: race between vfs_rename and do

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Message-ID: <CAE9vp3LT6s+qASCyF2-dEjD4caR67NLT15ad+SXi1fPPGxS-tg@mail.gmail.com>
Date:   Tue, 15 Feb 2022 17:56:35 +0100
From:   Xavier Roche <xavier.roche@...olia.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Miklos Szeredi <miklos@...redi.hu>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: race between vfs_rename and do_linkat (mv and link)

On Tue, Feb 15, 2022 at 5:06 PM Al Viro <viro@...iv.linux.org.uk> wrote:
> Does POSIX actually make any promises in that area?

My understanding is that we inherit from the mandatory atomicity of
all rename calls
(https://pubs.opengroup.org/onlinepubs/000095399/functions/rename.html)
> That specification requires that the action of the function be atomic.

We also inherit from the link call that is required to be atomic
(https://pubs.opengroup.org/onlinepubs/009695399/functions/link.html)
> The link() function shall atomically create a new link for the existing file and the link count of the file shall be incremented by one