linux-kernel - Re: open(2) says O_DIRECT works on 512 byte boundries?

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: <4980FB4D.9090009@shaw.ca>
Date:	Wed, 28 Jan 2009 18:41:49 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Greg KH <public-greg-U8xfFu+wG4EAvxtiuMwx3w@...h.gmane.org>
CC:	public-mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@...h.gmane.org,
	public-linux-man-u79uwXL29TY76Z2rM5mHXA@...h.gmane.org,
	public-linux-kernel-u79uwXL29TY76Z2rM5mHXA@...h.gmane.org
Subject: Re: open(2) says O_DIRECT works on 512 byte boundries?



Greg KH wrote:
> In looking at open(2), it says that O_DIRECT works on 512 byte boundries
> with the 2.6 kernel release:
> 	Under Linux 2.4, transfer sizes, and the alignment of the user
> 	buffer and  the file offset must all be multiples of the logical
> 	block size of the file system.  Under Linux 2.6, alignment  to
> 	512-byte  boundaries suffices.
> 
> However if you try to access an O_DIRECT opened file with a buffer that
> is PAGE_SIZE aligned + 512 bytes, it fails in a bad way (wrong data is
> read.)
> 
> Is this just a mistake in the documentation?  Or am I reading it
> incorrectly?
> 
> I have a test program that shows this if anyone wants it.

Well, it sounds like a bug to me.. even if it's not supported, if you do 
such an access, surely the kernel should detect that and return EINVAL 
or something rather than reading corrupted data..

--
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/