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

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Date:   Fri, 25 Nov 2022 21:00:17 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Zhen Lei <thunder.leizhen@...wei.com>
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 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
following commit message:

--------------------------------
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?