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

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Message-ID: <c03227b3-1c79-d214-5880-19f2f1ea0491@arm.com>
Date:   Thu, 29 Nov 2018 16:49:18 +0000
From:   Dave Rodgman <dave.rodgman@....com>
To:     "dsterba@...e.cz" <dsterba@...e.cz>, Yueyi Li <liyueyi@...e.com>,
        "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.

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.

Dave