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c=relaxed/simple; d=kernel.org; s=k20201202; t=1687072628; bh=RUSkoYlZfJnev8VRU+EmUs/ebvB9btIgUAlONEIMtM8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=etEo+Rb8zFXyDvlBxHmWa0x8QGgougagp0LL87PgoPX7k4q9TP7JOWNKjk6flVhRA uSRL/mb6CPoMUEISUDYk3DZ5QJFjfFSaJ1NJc2J+pWl2yxJX7f1YoNnp5nVXVXIGds Zmrvuan0ojIo48H0TzVVIpN0yxRDQ1oPXqrOQ/HAmx6ehNzv2WxkveVoNlRW4XxXCA YbyIVsRlOtx1DRNEruqxugMWgxwuNrHH1/+JB/2JptLgTCSJqZCIsRzhILRYgFFlQ4 LyPBuEumLbCzedGUDTnP+nN/484PhXhcjLPbq1rYI55bJYCdB15RgcFxjfMpVDOIPL tPGhmLToT+CyA== Date: Sun, 18 Jun 2023 10:16:27 +0300 From: Mike Rapoport To: Liam Ni Cc: Andrew Morton , dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm/sparse:avoid null pointer access in memory_present() Message-ID: <20230618071627.GZ52412@kernel.org> References: <20230617044036.3985524-1-zhiguangni01@gmail.com> <20230616224407.863c74a3dc9d4f1427802f91@linux-foundation.org> <20230617070051.GU52412@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspam-User: X-Stat-Signature: 69tsh3efx7gzwkku8w48wpmnq6mutn1y X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B8E27A0004 X-HE-Tag: 1687072629-226254 X-HE-Meta: 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 s6KUiHQg OkCj1CLc7yCBdevrr/4Am/0xKUblTY3dMO45AnJ9AU/RzqMfGqdPIYBhG5nmnScX49Qlk+s9N1bHAzbVGO3HliNHM9HupewhqFyM84E34AHTKmYfyKMA6bO490TNmUeF6PO7HohssCmew1MPjer5XMTtpSXzL6vMdkVdfCjGGz58b8cGgNWTkHrTo1qUm16nwOSmoOkY7sxaO30ZaRtgKzDfwXZDkJ8rwweLFxEvIvr0PNaHoJFgYiEARGeZrJhcpr4W/SmThC8S+qrEW059T5EEVcj/ebERM4+iWuYcNthhDw6DWXkzRvqW35TiFo90uMj1DsSfwNgxLw2ekdHPXeMirOJzdlSfuo4iIXdrJmuIX1C5Bdc6HHACc+27hn86LDp6fuZSrfFIzZ03JhijV9pAkIyGxRAtcIbTVQ52Yd40vkuVziyLVOmyKJVlNmm4EyzVC9WBmFV6/Q7hscCJS4Tebwck7LTz6IcQl X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Jun 17, 2023 at 04:59:46PM +0800, Liam Ni wrote: > On Sat, 17 Jun 2023 at 15:01, Mike Rapoport wrote: > > > > On Sat, Jun 17, 2023 at 02:17:58PM +0800, Liam Ni wrote: > > > On Sat, 17 Jun 2023 at 13:44, Andrew Morton wrote: > > > > > > > > On Sat, 17 Jun 2023 14:40:36 +1000 Liam Ni wrote: > > > > > > > > > __nr_to_section() may return a null pointer, > > > > > before accessing the member variable section_mem_map, > > > > > we should first determine whether it is a null pointer. > > > > > > > > > > ... > > > > > > > > > > --- a/mm/sparse.c > > > > > +++ b/mm/sparse.c > > > > > @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en > > > > > set_section_nid(section, nid); > > > > > > > > > > ms = __nr_to_section(section); > > > > > - if (!ms->section_mem_map) { > > > > > + if (ms && !ms->section_mem_map) { > > > > > ms->section_mem_map = sparse_encode_early_nid(nid) | > > > > > SECTION_IS_ONLINE; > > > > > __section_mark_present(ms, section); > > > > > > > > I'm suspecting that if __nr_to_section() returns NULL here, we should > > > > just panic. But a null-deref gives the same information, so why change > > > > things? > > > > > > Do you mean if ms is a null pointer，ms->section_mem_map will cause > > > system panic,so we needn't change? > > > > Yes, if __nr_to_section ever returns NULL the system will crash anyway. > > I got it,do we need to print some information by panic()? Accessing a NULL pointer will cause panic and there will be lots of information spilled into the log anyway. -- Sincerely yours, Mike.