linux-kernel - Re: [PATCH] Describe race of direct read and fork for unaligned buffers

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]

Date:	Wed, 2 May 2012 05:56:50 +1200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
	linux-man@...r.kernel.org, linux-mm@...ck.org, mgorman@...e.de,
	Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH] Describe race of direct read and fork for unaligned buffers

On Wed, May 2, 2012 at 4:15 AM, KOSAKI Motohiro
<kosaki.motohiro@...il.com> wrote:
>> +suffices. However, if the user buffer is not page aligned and direct read
>
> One more thing. direct write also makes data corruption. Think
> following scenario,

In the light of all of the comments, can someone revise the man-pages
patch that Jan sent?

Thanks,

Michael


> 1) P1-T1 uses DIO write (and starting dma)
> 2) P1-T2 call fork() and makes P2
> 3) P1-T3 write to the dio target page. and then, cow break occur and
> original dio target
>    pages is now owned by P2.
> 4) P2 write the dio target page. It now does NOT make cow break. and
> now we break
>    dio target page data.
> 5) DMA transfer write invalid data to disk.
>
> The detail is described in your refer URLs.
>
>
>> +runs in parallel with a
>> +.BR fork (2)
>> +of the reader process, it may happen that the read data is split between
>> +pages owned by the original process and its child. Thus effectively read
>> +data is corrupted.
>>  .LP
>>  The
>>  .B O_DIRECT



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/