linux-kernel - Re: Interface for the new fallocate() system call

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Message-ID: <Pine.LNX.4.64.0703291134070.6730@woody.linux-foundation.org>
Date:	Thu, 29 Mar 2007 11:37:03 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
cc:	"linux-os (Dick Johnson)" <linux-os@...logic.com>,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>,
	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
	xfs@....sgi.com, suparna@...ibm.com, cmm@...ibm.com
Subject: Re: Interface for the new fallocate() system call

On Thu, 29 Mar 2007, Jan Engelhardt wrote:
>
> I have to disagree, since wrapping it into a struct and copying the struct
> in kernelspace from userspace requires more code.

Not just more code, but more security issues too.

Passing system call arguments by value means that there are no subtle 
security issues - the value you use is the value you got. But once you 
pass-by-reference, you have to make damn sure that you do the proper user 
space accesses and verify the pointer correctly.

User-space (aka "user-supplied") pointers are just more dangerous. We 
obviously can't avoid them, but they need much more care than just a 
random value directly passed in a register.

		Linus
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