linux-kernel - Re: [PATCH RFC 1/4] block: Make bdev_can_atomic_write() robust against mis-aligned bdev size

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] [day] [month] [year] [list]

Message-ID: <a8e47dd4-26f4-49da-9ba8-aad2e8fcf9b1@suse.de>
Date: Fri, 13 Sep 2024 10:36:30 +0200
From: Hannes Reinecke <hare@...e.de>
To: John Garry <john.g.garry@...cle.com>, Christoph Hellwig <hch@....de>
Cc: axboe@...nel.dk, song@...nel.org, yukuai3@...wei.com, kbusch@...nel.org,
 sagi@...mberg.me, James.Bottomley@...senPartnership.com,
 martin.petersen@...cle.com, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
 linux-nvme@...ts.infradead.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH RFC 1/4] block: Make bdev_can_atomic_write() robust
 against mis-aligned bdev size

On 9/12/24 17:22, John Garry wrote:
> On 12/09/2024 16:07, Christoph Hellwig wrote:
>>> We should do be able to, but with this patch we cannot. However, a
>>> misaligned partition would be very much unexpected.
>> Yes, misaligned partitions is very unexpected, but with large and
>> potentially unlimited atomic boundaries I would not expect the size
>> to always be aligned.  But then again at least in NVMe atomic writes
>> don't need to match the max size anyway, so I'm not entirely sure
>> what the problem actually is.
> 
> Actually it's not an alignment issue, but a size issue.
> 
> Consider a 3.5MB partition and atomic write max is 1MB. If we tried to 
> atomic write 1MB at offset 3MB, then it would be truncated to a 0.5MB 
> write.
> 
> So maybe it is an application bug.
> 
Hmm. Why don't we reject such an I/O? We cannot guarantee an atomic 
write, so I think we should be perfectly fine to return an error to
userspace.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich