linux-kernel - Re: [PATCH v2] mmap: Fix do_brk_flags() modifying obviously incorrect VMAs

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Message-Id: <20221205123250.3fc552d96fcca5dc58be8443@linux-foundation.org>
Date:   Mon, 5 Dec 2022 12:32:50 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Liam Howlett <liam.howlett@...cle.com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Yu Zhao <yuzhao@...gle.com>, Jason Donenfeld <Jason@...c4.com>,
        Matthew Wilcox <willy@...radead.org>,
        SeongJae Park <sj@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v2] mmap: Fix do_brk_flags() modifying obviously
 incorrect VMAs

On Mon, 5 Dec 2022 19:23:17 +0000 Liam Howlett <liam.howlett@...cle.com> wrote:

> Add more sanity checks to the VMA that do_brk_flags() will expand.
> Ensure the VMA matches basic merge requirements within the function
> before calling can_vma_merge_after().

I't unclear what's actually being fixed here.

Why do you feel we need the above changes?

> Drop the duplicate checks from vm_brk_flags() since they will be
> enforced later.
> 
> Fixes: 2e7ce7d354f2 ("mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()")

Fixes in what way?  Removing the duplicate checks?