linux-kernel - Re: [PATCH AUTOSEL for 3.18 044/102] fix race in drivers/char/random.c:get

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Message-ID: <20180321181316.v55ryf7ekck3rgwy@sasha-lappy>
Date:   Wed, 21 Mar 2018 18:13:18 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Michael Schmitz <schmitzmic@...il.com>,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH AUTOSEL for 3.18 044/102] fix race in
 drivers/char/random.c:get_reg()

On Tue, Mar 20, 2018 at 10:48:48AM +0100, Geert Uytterhoeven wrote:
>Hi Sasha,
>
>On Mon, Mar 19, 2018 at 5:12 PM, Sasha Levin
><Alexander.Levin@...rosoft.com> wrote:
>> From: Michael Schmitz <schmitzmic@...il.com>
>>
>> [ Upstream commit 9dfa7bba35ac08a63565d58c454dccb7e1bb0a08 ]
>>
>> get_reg() can be reentered on architectures with prioritized interrupts
>> (m68k in this case), causing f->reg_index to be incremented after the
>> range check. Out of bounds memory access past the pt_regs struct results.
>> This will go mostly undetected unless access is beyond end of memory.
>>
>> Prevent the race by disabling interrupts in get_reg().
>>
>> Tested on m68k (Atari Falcon, and ARAnyM emulator).
>>
>> Kudos to Geert Uytterhoeven for helping to trace this race.
>>
>> Signed-off-by: Michael Schmitz <schmitzmic@...il.com>
>> Signed-off-by: Theodore Ts'o <tytso@....edu>
>> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
>
>You probably want to apply follow-up commit 92e75428ffc90e2a
>("random: use lockless method of accessing and updating f->reg_idx"), too.

I've grabbed it too, thanks!

-- 

Thanks,
Sasha