linux-kernel - Re: [PATCH] scsi: int overflow in st

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Date:	Tue, 17 Dec 2013 19:53:52 +0200
From:	"Kai Mäkisara (Kolumbus)" 
	<kai.makisara@...umbus.fi>
To:	xuyongjiande@...il.com
Cc:	"James E.J. Bottomley" <JBottomley@...allels.com>,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH] scsi: int overflow in st_ioctl()

On 17.12.2013, at 16.43, Yongjian Xu xuyongjiande@...il.com wrote:

> From: Yongjian Xu <xuyongjiande@...il.com>
> 
> mtc.mt_count comes from user-space.
> int overflow may occur:
> mtc.mt_count++;
> mtc.mt_count—;

I agree that this is a problem. However, it seems that there is also another problem: the SPACE command uses a 24-bit count field and this overflows far below INT_MAX. Should the count in MTFSF etc. be limited to (2<<24-2)? This would make the checks you suggest unnecessary. (-2 so that the behavior does not depend on whether we are at file mark or not.)

I am a bit hesitant with this suggestion because someone may use count INT_MAX to space to the end of the tape. This probably succeeds now but after the fix it would return an error.

Thanks,
Kai

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