linux-ext4 - Journal async commit broken for data=ordered?

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-next>] [day] [month] [year] [list]

Message-ID: <20120214155536.GA16561@quack.suse.cz>
Date:	Tue, 14 Feb 2012 16:55:36 +0100
From:	Jan Kara <jack@...e.cz>
To:	linux-ext4@...r.kernel.org
Cc:	Ted Tso <tytso@....edu>
Subject: Journal async commit broken for data=ordered?

  Hello,

  I've just realized that JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT breaks
guarantees of data=ordered mode in ext4. The problem is that async commit
code assumes that when a checksum of a transaction in the journal matches,
all necessary data is on disk. This is true for metadata but need not be so
for data - the whole transaction may be correctly on pernament storage
while some data is still sitting in drive's caches. Thus if a power failure
happens at that moment, we have broken guarantees of data=ordered mode.
Seeing that async commit code isn't used by default anyway (I remember
there used to be some problems with it), shouldn't we just rip it out?

								Honza
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html