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Sender: Tejun Heo <htejun@gmail.com>
Date: Thu, 4 Apr 2024 06:51:51 -1000
From: Tejun Heo <tj@kernel.org>
To: Rik van Riel <riel@surriel.com>
Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com,
	Jens Axboe <axboe@kernel.dk>, Josef Bacik <josef@toxicpanda.com>,
	cgroups@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re: [PATCH] blk-iocost: avoid out of bounds shift
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On Thu, Apr 04, 2024 at 12:32:53PM -0400, Rik van Riel wrote:
> UBSAN catches undefined behavior in blk-iocost, where sometimes
> iocg->delay is shifted right by a number that is too large,
> resulting in undefined behavior on some architectures.
> 
> [  186.556576] ------------[ cut here ]------------
> UBSAN: shift-out-of-bounds in block/blk-iocost.c:1366:23
> shift exponent 64 is too large for 64-bit type 'u64' (aka 'unsigned long long')
> CPU: 16 PID: 0 Comm: swapper/16 Tainted: G S          E    N 6.9.0-0_fbk700_debug_rc2_kbuilder_0_gc85af715cac0 #1
> Hardware name: Quanta Twin Lakes MP/Twin Lakes Passive MP, BIOS F09_3A23 12/08/2020
> Call Trace:
>  <IRQ>
>  dump_stack_lvl+0x8f/0xe0
>  __ubsan_handle_shift_out_of_bounds+0x22c/0x280
>  iocg_kick_delay+0x30b/0x310
>  ioc_timer_fn+0x2fb/0x1f80
>  __run_timer_base+0x1b6/0x250
> ...
> 
> Avoid that undefined behavior by simply taking the
> "delay = 0" branch if the shift is too large.
> 
> I am not sure what the symptoms of an undefined value
> delay will be, but I suspect it could be more than a
> little annoying to debug.
> 
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Josef Bacik <josef@toxicpanda.com>
> Cc: Jens Axboe <axboe@kernel.dk>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun