linux-kernel - Re: drivers: random: Shift out-of-bounds in _mix_pool

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Message-ID: <20141020140818.GB23177@thunk.org>
Date:	Mon, 20 Oct 2014 10:08:18 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michal Marek <mmarek@...e.cz>,
	Sasha Levin <sasha.levin@...cle.com>, x86@...nel.org,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Khlebnikov <koct9i@...il.com>
Subject: Re: drivers: random: Shift out-of-bounds in _mix_pool_bytes

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
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