linux-kernel - Re: [PATCH v2] ubifs: Handle re-linking of inodes correctly while recovery

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Message-ID: <CACna6ryKs4LcSK8-FY3MB27O4b7MJqVROaSTQKtpGkqqZoQS7g@mail.gmail.com>
Date:   Thu, 15 Nov 2018 12:49:44 +0100
From:   Rafał Miłecki <zajec5@...il.com>
To:     Richard Weinberger <richard@....at>
Cc:     linux-mtd@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stable <stable@...r.kernel.org>,
        Russell Senior <russell@...sonaltelco.net>
Subject: Re: [PATCH v2] ubifs: Handle re-linking of inodes correctly while recovery

On Wed, 7 Nov 2018 at 23:04, Richard Weinberger <richard@....at> wrote:
> UBIFS's recovery code strictly assumes that a deleted inode will never
> come back, therefore it removes all data which belongs to that inode
> as soon it faces an inode with link count 0 in the replay list.
> Before O_TMPFILE this assumption was perfectly fine. With O_TMPFILE
> it can lead to data loss upon a power-cut.
>
> Consider a journal with entries like:
> 0: inode X (nlink = 0) /* O_TMPFILE was created */
> 1: data for inode X /* Someone writes to the temp file */
> 2: inode X (nlink = 0) /* inode was changed, xattr, chmod, … */
> 3: inode X (nlink = 1) /* inode was re-linked via linkat() */
>
> Upon replay of entry #2 UBIFS will drop all data that belongs to inode X,
> this will lead to an empty file after mounting.
>
> As solution for this problem, scan the replay list for a re-link entry
> before dropping data.
>
> Fixes: 474b93704f32 ("ubifs: Implement O_TMPFILE")
> Cc: stable@...r.kernel.org
> Cc: Russell Senior <russell@...sonaltelco.net>
> Cc: Rafał Miłecki <zajec5@...il.com>
> Reported-by: Russell Senior <russell@...sonaltelco.net>
> Reported-by: Rafał Miłecki <zajec5@...il.com>
> Signed-off-by: Richard Weinberger <richard@....at>

Thank you!!!

Tested-by: Rafał Miłecki <rafal@...ecki.pl>