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From:   Richard Weinberger <richard@nod.at>
To:     Hou Tao <houtao1@huawei.com>
Cc:     linux-mtd@lists.infradead.org, dwmw2@infradead.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] jffs2: Fix integer underflow in jffs2_rtime_compress
Date:   Thu, 20 Dec 2018 11:45:37 +0100
Message-ID: <2142335.HPRDAJu19m@blindfold>
In-Reply-To: <cae86ca1-91f9-6728-df64-40580145220d@huawei.com>
References: <20181215162350.12489-1-richard@nod.at> <cae86ca1-91f9-6728-df64-40580145220d@huawei.com>
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Am Donnerstag, 20. Dezember 2018, 11:43:08 CET schrieb Hou Tao:
> 
> On 2018/12/16 0:23, Richard Weinberger wrote:
> > The rtime compressor assumes that at least two bytes are
> > compressed.
> > If we try to compress just one byte, the loop condition will
> > wrap around and an out-of-bounds write happens.
> > 
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Richard Weinberger <richard@nod.at>
> > ---
> >  fs/jffs2/compr_rtime.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > It seems that it doesn't incur any harm because the minimal allocated
> size will be 8-bytes and jffs2_rtime_compress() will write 2-bytes into
> the allocated buffer.

Are you sure about that? I saw odd kernel behavior and KASAN complained too.

Thanks,
//richard