linux-kernel - Re: [PATCH v2 1/2] ras: fix an off-by-one error in __find

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Message-ID: <20190416214634.GP31772@zn.tnic>
Date:   Tue, 16 Apr 2019 23:46:34 +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 v2 1/2] ras: fix an off-by-one error in __find_elem()

On Tue, Apr 16, 2019 at 02:33:50PM -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 right after the while loop. In this case,
> we should not even read it, just return -ENOKEY instead.
> 
> Note, this could cause a kernel crash if ce_arr.n is exactly
> MAX_ELEMS.

"Could cause"?

I'm still waiting for a demonstration. You can build a case through
writing values in the debugfs nodes I pointed you at or even with a
patch ontop preparing the exact conditions for it to crash. And then
give me that "recipe" to trigger it here in a VM.

Thx.

-- 
Regards/Gruss,
    Boris.

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