On 17.12.2013, at 16.43, Yongjian Xu xuyongjia...@gmail.com wrote:

> From: Yongjian Xu <xuyongjia...@gmail.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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