linux-kernel - Re: KASAN: stack-out-of-bounds Write in mpol_to

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Message-ID: <110bb9ab-9765-1c5b-39c6-3644cb1b99a4@infradead.org>
Date:   Wed, 25 Mar 2020 17:54:48 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Entropy Moe <3ntr0py1337@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: KASAN: stack-out-of-bounds Write in mpol_to_str

On 3/20/20 1:36 AM, Entropy Moe wrote:
> Hello Randy,
> please see attached POC for the vulnerability.
> 

Hi Moe,

Do you have anything to do with the syzkaller source code generation? (POC; reproducers)

I don't expect it to be beautiful, but it could be a lot easier to read in a few places.

E.g., the POC that you provided sets a tmpfs mount option string to
"mpol=prefer:,", which is probably purposely malformed (OK), but it does
so in an unreadable manner: (I added the // comments.)

memcpy((void*)0x20000340, "mpol", 4);
*(uint8_t*)0x20000344 = 0x3d; // =
memcpy((void*)0x20000345, "prefer", 6);
*(uint8_t*)0x2000034b = 0x3a; // :
*(uint8_t*)0x2000034c = 0x2c; // ,
*(uint8_t*)0x2000034d = 0;


That kind of obfuscation just helps slow down debugging. :(

-- 
~Randy