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Date:   Tue, 5 Mar 2019 07:56:31 -0800
From:   Tejun Heo <>
To:     Konstantin Khlebnikov <>
Cc:     Jens Axboe <>,,, Li Zefan <>,
        Johannes Weiner <>,
Subject: Re: [PATCH] blk-throttle: verify format of bandwidth limit and
 detect overflows

Hello, Konstantin.

On Wed, Feb 27, 2019 at 11:05:44AM +0300, Konstantin Khlebnikov wrote:
> Unlike to memory cgroup blkio throttler does not support value suffixes.
> It silently ignores everything after last digit. For example this command
> will set rate limit 1 byte per second rather than 1 megabyte per second:
> # echo "7:0 1M" > blkio.throttle.read_bps_device
> # cat blkio.throttle.read_bps_device
> 7:0 1
> Cgroup2 interface has the same flaw:
> # echo "7:0 rbps=1M" > io.max
> # cat io.max
> 7:0 rbps=1 wbps=max riops=max wiops=max
> Also sscanf does not care much about overflows.
> This patch uses modern function kstrtou64 for parsing.
> It rejects trailing garbage and detects integer overflows.
> Also this patch handles iops limit overflows for cgroup-v1 in the same as
> cgroup-v2: limits >= UINT_MAX becomes unlimited.
> Fixes: 2ee867dcfa2e ("blkcg: implement interface for the unified hierarchy")
> Signed-off-by: Konstantin Khlebnikov <>

So, I'd much rather keep the parsing implementations simple.  Unless
there's a correctness problem (you mentioned overflowing, how would
that happen?), the simpler the better.  I don't think the kernel needs
to be in the business of strict input verification here.



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