linux-kernel - Re: [PATCH 4/5] idr: Handle integer overflow correctly

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Message-ID: <20191103114140.GD15832@bombadil.infradead.org>
Date:   Sun, 3 Nov 2019 03:41:40 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     linux-kernel@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH 4/5] idr: Handle integer overflow correctly

On Sun, Nov 03, 2019 at 03:40:11AM -0800, Matthew Wilcox wrote:
> If there is an entry at INT_MAX then idr_for_each_entry() will increment
> id after handling it.  This is undefined behaviour, and is caught by
> UBSAN.  Adding 1U to id forces the operation to be carried out as an
> unsigned addition which (when assigned to id) will result in INT_MIN.
> Since there is never an entry stored at INT_MIN, idr_get_next() will
> return NULL, ending the loop as expected.

This was an earlier version which got left around in the git format-patch
directory.  Please ignore.