linux-kernel - Re: brk() in v6.1-rc1 can expand file mappings, seemingly without taking file locks

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Message-ID: <CAG48ez190wrwM57AiC6dsxtXYu84OcSgJOAc+q8a9H5pntoq7Q@mail.gmail.com>
Date:   Fri, 2 Dec 2022 20:42:39 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Linux-MM <linux-mm@...ck.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        Jason Donenfeld <Jason@...c4.com>, Yu Zhao <yuzhao@...gle.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        SeongJae Park <sj@...nel.org>, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: brk() in v6.1-rc1 can expand file mappings, seemingly without
 taking file locks

On Fri, Dec 2, 2022 at 7:53 PM Jann Horn <jannh@...gle.com> wrote:
> As of commit ca57f02295f, brk() can expand ordinary file mappings (but

Sorry, that was worded confusingly - I meant "ca57f02295f is the
commit from Linus' tree on top of which I was testing".

The broken code seems to have been introduced in
commit 2e7ce7d354f2 ("mm/mmap: change do_brk_flags() to expand
existing VMA and add do_brk_munmap()").