linux-kernel - Re: [PATCH] fs: buffer: set the expression type to unsigned long in folio_create

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: <20240717134100.wvekl66w7j2eatec@quack3>
Date: Wed, 17 Jul 2024 15:41:00 +0200
From: Jan Kara <jack@...e.cz>
To: Matthew Wilcox <willy@...radead.org>
Cc: Sergey Shtylyov <s.shtylyov@....ru>, Roman Smirnov <r.smirnov@....ru>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	lvc-project@...uxtesting.org
Subject: Re: [PATCH] fs: buffer: set the expression type to unsigned long in
 folio_create_buffers()

On Tue 16-07-24 16:51:17, Matthew Wilcox wrote:
> On Tue, Jul 16, 2024 at 06:41:49PM +0300, Sergey Shtylyov wrote:
> >    And here we'll have at least one potential problem (that you neglected
> > to describe): with 1 << 31, that 1 will land in a sign bit and then, when
> > it's implicitly cast to *unsigned long*, the 32-bit value will be sign-
> > extended to 64-bit on 64-bit arches) and then we'll have an incorrect size
> > (0xffffffff80000000) passed to create_empty_buffers()...
> 
> Tell me more about this block device you have with a 2GB block size ... ?
> 
> (ie note that this is a purely theoretical issue)

Yeah, this just does not make huge amount of sense. Maybe a proper fix
would be to just make blocksize uint? There are a lot of places where
blocksize is actually stored in a 32-bit type...

								Honza

> 
> > > to use 1UL instead.
> > 
> >    Perphas was worth noting that using 1UL saves us 1 movsx instruction on
> > x86_64...
> 
> That is a worthwhile addition to the change log.
> 
> Also, you should cc the person who wrote that code, ie me.
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR