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Date: Mon, 20 Oct 2014 10:08:18 -0400
From: Theodore Ts'o <tytso@mit.edu>
Subject: Re: drivers: random: Shift out-of-bounds in _mix_pool_bytes
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To: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Peter Zijlstra <peterz@infradead.org>, Michal Marek <mmarek@suse.cz>, Sasha Levin <sasha.levin@oracle.com>, x86@kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Andreas Dilger <adilger.kernel@dilger.ca>, Dmitry Vyukov <dvyukov@google.com>, Konstantin Khlebnikov <koct9i@gmail.com>

On Mon, Oct 20, 2014 at 05:58:25PM +0400, Andrey Ryabinin wrote:
> It's triggering when input_rotate == 0, so UBSan complains about right shift in rol32()
> 
> static inline __u32 rol32(__u32 word, unsigned int shift)
> {
> 	return (word << shift) | (word >> (32 - shift));
> }

Ah, thanks; I don't know why I didn't see that.

So the only real question is whether we fix it in the call to rol32,
or in the rol32 function itself (i.e):

static inline __u32 rol32(__u32 word, unsigned int shift)
{
	return shift ? ((word << shift) | (word >> (32 - shift))) : word;
}

Dos that make sense to everyone?

						- Ted