linux-kernel - Re: [PATCH 1/2] ras: fix an off-by-one error in __find

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Message-ID: <20190416090726.GD27892@zn.tnic>
Date:   Tue, 16 Apr 2019 11:07:26 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] ras: fix an off-by-one error in __find_elem()

On Mon, Apr 15, 2019 at 06:20:00PM -0700, Cong Wang wrote:
> ce_arr.array[] is always within the range [0, ce_arr.n-1].
> However, the binary search code in __find_elem() uses ce_arr.n
> as the maximum index, which could lead to an off-by-one
> out-of-bound access when the element after the last is exactly
> the one just got deleted, that is, 'min' returned to caller as
> 'ce_arr.n'.

Sorry, I don't follow.

There's a debugfs interface in /sys/kernel/debug/ras/cec/ with which you
can input random PFNs and test the thing.

Show me pls how this can happen with an example.

Thx.

-- 
Regards/Gruss,
    Boris.

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