linux-ext4 - Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200312000716.GY10737@dread.disaster.area>
Date:   Thu, 12 Mar 2020 11:07:17 +1100
From:   Dave Chinner <david@...morbit.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        Linux Filesystem Development List 
        <linux-fsdevel@...r.kernel.org>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org
Subject: Re: [PATCH] writeback: avoid double-writing the inode on a lazytime
 expiration

On Wed, Mar 11, 2020 at 08:57:49AM -0400, Theodore Y. Ts'o wrote:
> On Tue, Mar 10, 2020 at 08:20:09PM -0700, Eric Biggers wrote:
> > Thanks Ted!  This fixes the fscrypt test failure.
> > 
> > However, are you sure this works correctly on all filesystems?  I'm not sure
> > about XFS.  XFS only implements ->dirty_inode(), not ->write_inode(), and in its
> > ->dirty_inode() it does:
>   ...
> > 		if (flag != I_DIRTY_SYNC || !(inode->i_state & I_DIRTY_TIME))
> > 			return;
> 
> That's true, but when the timestamps were originally modified,
> dirty_inode() will be called with flag == I_DIRTY_TIME, which will
> *not* be a no-op; which is to say, XFS will force the timestamps to be
> updated on disk when the timestamps are first dirtied, because it
> doesn't support I_DIRTY_TIME.

We log the initial timestamp change, and then ignore timestamp
updates until the dirty time expires and the inode is set
I_DIRTY_SYNC via __mark_inode_dirty_sync(). IOWs, on expiry, we have
time stamps that may be 24 hours out of date in memory, and they
still need to be flushed to the journal.

However, your change does not mark the inode dirtying on expiry
anymore, so...

> So I think we're fine.

... we're not fine. This breaks XFS and any other filesystem that
relies on a I_DIRTY_SYNC notification to handle dirty time expiry
correctly.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com