linux-kernel - Re: [PATCH v3 0/2] fs: clear a UBSAN shift-out-of-bounds warning

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Message-ID: <0a8264a8-e2a9-952a-97ce-a7f06920ad39@huawei.com>
Date:   Sat, 26 Nov 2022 09:59:06 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Al Viro <viro@...iv.linux.org.uk>
CC:     Eric Biggers <ebiggers@...nel.org>,
        <linux-fsdevel@...r.kernel.org>, "Chris Mason" <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, <linux-btrfs@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/2] fs: clear a UBSAN shift-out-of-bounds warning



On 2022/11/26 5:00, Al Viro wrote:
> On Fri, Nov 25, 2022 at 05:13:56PM +0800, Zhen Lei wrote:
>> v2 --> v3:
>> Updated the commit message of patch 2/2 based on Alexander Viro's suggestion.
> 
> Not exactly what I meant...  I've tentatively applied it, with the

Haha, I felt like something was missing yesterday, too. But as far as my English
level is concerned, I usually copy the words suggested by others directly.

> following commit message:

Thanks.

> 
> --------------------------------
> get rid of INT_LIMIT, use type_max() instead
> 
> INT_LIMIT() tries to do what type_max() does, except that type_max()
> doesn't rely upon undefined behaviour[*], might as well use type_max()
> instead.
> 
> [*] if T is an N-bit signed integer type, the maximal value in T is
> pow(2, N - 1) - 1, all right, but naive expression for that value
> ends up with a couple of wraparounds and as usual for wraparounds
> in signed types, that's an undefined behaviour.  type_max() takes
> care to avoid those...
> 
> Caught-by: UBSAN
> Suggested-by: Eric Biggers <ebiggers@...nel.org>
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> Reviewed-by: Eric Biggers <ebiggers@...gle.com>
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> --------------------------------
> 
> Does anybody have objections against the commit message above?

Looks good to me.

> 
> .
> 

-- 
Regards,
  Zhen Lei