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From: Borislav Petkov <bp@alien8.de>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org,
	Tony Luck <tony.luck@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: [v2,1/2] ras: fix an off-by-one error in __find_elem()
Date: Tue, 16 Apr 2019 23:46:34 +0200	[thread overview]
Message-ID: <20190416214634.GP31772@zn.tnic> (raw)

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.

WARNING: multiple messages have this Message-ID (diff)
From: Borislav Petkov <bp@alien8.de>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org,
	Tony Luck <tony.luck@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v2 1/2] ras: fix an off-by-one error in __find_elem()
Date: Tue, 16 Apr 2019 23:46:34 +0200	[thread overview]
Message-ID: <20190416214634.GP31772@zn.tnic> (raw)
Message-ID: <20190416214634.4CnLLdyGfDXCZuGKfzuyuxsaSeA_Vafnh9cP4TaWxnw@z> (raw)
In-Reply-To: <20190416213351.28999-1-xiyou.wangcong@gmail.com>

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.

Good mailing practices for 400: avoid top-posting and trim the reply.

         reply	other threads:[~2019-04-16 21:46 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-16 21:33 [v2,1/2] ras: fix an off-by-one error in __find_elem() Cong Wang
2019-04-16 21:33 ` [PATCH v2 1/2] " Cong Wang
2019-04-16 21:33 ` [v2,2/2] ras: close the race condition with timer Cong Wang
2019-04-16 21:33   ` [PATCH v2 2/2] " Cong Wang
2019-06-08 15:28   ` [tip:ras/urgent] RAS/CEC: Convert the timer callback to a workqueue tip-bot for Cong Wang
2019-04-16 21:46 ` Borislav Petkov [this message]
2019-04-16 21:46   ` [PATCH v2 1/2] ras: fix an off-by-one error in __find_elem() Borislav Petkov
2019-04-16 23:16   ` [v2,1/2] " Cong Wang
2019-04-16 23:16     ` [PATCH v2 1/2] " Cong Wang
2019-04-20 11:34     ` [v2,1/2] " Borislav Petkov
2019-04-20 11:34       ` [PATCH v2 1/2] " Borislav Petkov
2019-04-20 18:25       ` [v2,1/2] " Cong Wang
2019-04-20 18:25         ` [PATCH v2 1/2] " Cong Wang
2019-04-20 19:04         ` [v2,1/2] " Borislav Petkov
2019-04-20 19:04           ` [PATCH v2 1/2] " Borislav Petkov
2019-04-20 19:15           ` [v2,1/2] " Cong Wang
2019-04-20 19:15             ` [PATCH v2 1/2] " Cong Wang
2019-04-21  8:27             ` [v2,1/2] " Borislav Petkov
2019-04-21  8:27               ` [PATCH v2 1/2] " Borislav Petkov

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