linux-kernel - Re: [PATCH] posix-timers: Use array safe helper when fetching notification symbolic name

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Date:   Fri, 9 Nov 2018 12:28:11 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andrey Vagin <avagin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] posix-timers: Use array safe helper when fetching
 notification symbolic name

On Fri, Nov 09, 2018 at 10:18:25AM +0100, Thomas Gleixner wrote:
> > +	nidx = array_index_nospec(notify & ~SIGEV_THREAD_ID, ARRAY_SIZE(nstr));
> 
> I completely understand your intention, but this is misleading. The above
> is really not a speculation gadget.
> 
> I'd rather do an open coded check here and fail the thing instead of
> printing wrong information:
> 
>     	   nidx = timer->it_sigev_notify & ~SIGEV_THREAD_ID;
> 	   if (nidx >= ARRAY_SIZE(nstr))
> 	   	return -EINVAL;

Yes, I thought about such approach and did the similar code
in first place, then I dropped it because didn't want additional
"if"s here (your fix in the former commit already does all verification
needed). But thinking more I agree: this code is not time critical
and spending a few cycles won't hurt much. Will update, thanks Thomas!