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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH -next] fork: annotate a data race in vm_area_dup()
Date:   Tue, 18 Feb 2020 07:40:06 -0500
Message-Id: <93E6B243-9A0F-410C-8EE4-9D57E28AF5AF@lca.pw>
References: <20200218103002.6rtjreyqjepo3yxe@box>
Cc:     Andrew Morton <akpm@linux-foundation.org>, elver@google.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        peterz@infradead.org,
        syzbot+c034966b0b02f94f7f34@syzkaller.appspotmail.com,
        syzkaller-bugs@googlegroups.com
In-Reply-To: <20200218103002.6rtjreyqjepo3yxe@box>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Feb 18, 2020, at 5:29 AM, Kirill A. Shutemov <kirill@shutemov.name> wro=
te:
>=20
> I think I've got this:
>=20
> vm_area_dup() blindly copies all fields of orignal VMA to the new one.
> This includes coping vm_area_struct::shared.rb which is normally protected=

> by i_mmap_lock. But this is fine because the read value will be
> overwritten on the following __vma_link_file() under proper protectection.=


Right, multiple processes could share the same file-based address space wher=
e those vma have been linked into address_space::i_mmap via vm_area_struct::=
shared.rb. Thus, the reader could see its shared.rb linkage pointers got upd=
ated by other processes.

>=20
> So the fix is correct, but justificaiton is lacking.
>=20
> Also, I would like to more fine-grained annotation: marking with
> data_race() 200 bytes copy may hide other issues.

That is the harder part where I don=E2=80=99t think we have anything for tha=
t today. Macro, any suggestions? ASSERT_IGNORE_FIELD()?=