linux-kernel - Re: [PATCH v2] lzo: fix ip overrun during compress.

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Message-ID: <SN1PR13MB030426DBA527C725AE28B5A9DFD30@SN1PR13MB0304.namprd13.prod.outlook.com>
Date:   Fri, 30 Nov 2018 03:05:38 +0000
From:   Yueyi Li <liyueyi@...e.com>
To:     Dave Rodgman <dave.rodgman@....com>,
        "dsterba@...e.cz" <dsterba@...e.cz>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "w@....eu" <w@....eu>,
        "donb@...uritymouse.com" <donb@...uritymouse.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "markus@...rhumer.com" <markus@...rhumer.com>
CC:     nd <nd@....com>
Subject: Re: [PATCH v2] lzo: fix ip overrun during compress.

Hi Dave,


On 2018/11/30 0:49, Dave Rodgman wrote:
> On 28/11/2018 1:52 pm, David Sterba wrote:
>
>> The fix is adding a few branches to code that's supposed to be as fast
>> as possible. The branches would be evaluated all the time while
>> protecting against one signle bad page address. This does not look like
>> a good performance tradeoff.
> As an alternative, for all but the first case, instead of:
>
> if (unlikely(OVERFLOW_ADD_CHECK(ip, m_len) || (ip + m_len >= ip_end)))
>
> I'd suggest we do:
>
> if (unlikely((ip_end - ip) <= m_len))
>
> which will be about as efficient as what's currently there, but doesn't
> have issues with overflow.

Ooh, yes, pretty good solution to this, thanks.

> Dave

Thanks,
Yueyi