Re: file offset corruption on 32-bit machines?

[Matthew Wilcox <matthew@wil.cx>]

On Thu, Apr 10, 2008 at 04:31:09PM +0200, Jiri Kosina wrote:
> >   Well, this race is more subtle - the window is just one instruction
> > wide (stores to f_pos from CPU2 must come between the store of lower and
> > upper 32-bits of f_pos on CPU1). And the only result is that f_pos has
> > 32-bits from one file pointer and 32-bits from the other one. So I can
> > hardly imagine this would be exploitable...
> 
> Supposing you are not holding any spinlock and are running with 
> preemptible kernel (pretty common scenario nowadays), there is nothing 
> that would prevent kernel from rescheduling between the two instructions, 
> enlarging the race window to be more comfortable for attacker, right?
> 
> I think this is worth fixing.

Seems a lot like reading jiffies to me.  Is the seqlock the right
solution to use for fixing this?

-- 
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