linux-kernel - Re: [PATCH] fs: fix integer overflow in MS

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Date:	Sat, 21 Apr 2012 12:37:19 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs: fix integer overflow in MS_NOUSER definition

Al Viro wrote:
> On Sat, Apr 21, 2012 at 09:49:49AM +0400, Konstantin Khlebnikov wrote:
>> MS_NOUSER defined as signed int (1<<31), sb->s_flags declared as unsigned long.
>> So (sb->s_flags&  MS_NOUSER) works as (sb->s_flags&  0xffffffff80000000).
>
> ... and it's not a problem since we can't use bits 32 and above anyway -
> unsigned long is 32bit on a lot of platforms.  I have no objections to
> making that 1U<<31, but it's not a bug, let alone an integer overflow.

Yes, it's not a bug here, but I not sure about the rest thousand places, where
similar expressions are used. Probably checkpatch should warn about such things.

BTW this patch makes code smaller =)

add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-16 (-16)
function                                     old     new   delta
graft_tree                                   135     119     -16
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