Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
To:     Mika Westerberg <mika.westerberg@linux.intel.com>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Subject: Re: [PATCH v2 2/3] nvmem: check for NULL reg_read and reg_write
 before dereferencing
Thread-Topic: [PATCH v2 2/3] nvmem: check for NULL reg_read and reg_write
 before dereferencing
Thread-Index: AQHV8KlCqOzxWYRvokel+qEls5/4v6g2rAsAgAHvkoA=
Date:   Wed, 4 Mar 2020 16:03:46 +0000
Message-ID: <PSXP216MB0438A73D6C6EC2FF4EA102DE80E50@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM>
References: <PSXP216MB0438FE68DAAFC23CB9AAD5E180E70@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM>
 <PSXP216MB0438A1EEBF56DF852F18F14580E70@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM>
 <20200303102956.GM2540@lahna.fi.intel.com>
In-Reply-To: <20200303102956.GM2540@lahna.fi.intel.com>
Accept-Language: en-AU, en-US
Content-Language: en-US
x-ms-exchange-messagesentrepresentingtype: 1
x-tmn:  [KPldaVRASJ6VtKyeZMSCASjVbzWwbdHUPfv/b/1HhTthXUKWpA8kbYX83w03E6gA]
x-microsoft-original-message-id: <20200304160339.GA2300@nicholas-dell-linux>
x-ms-publictraffictype: Email
x-incomingheadercount: 50
x-eopattributedmessage: 0
x-ms-office365-filtering-correlation-id: 03e1d57e-6c06-4d45-f5d6-08d7c0559e99
x-ms-traffictypediagnostic: PU1APC01HT014:
x-microsoft-antispam: BCL:0;
x-microsoft-antispam-message-info: 4/8MDeVwazpXfn7iIVFOTIZznE4ZUh7+6LbpJwB3g21hl/t4+4wfsuSuudwrUFKyNuXk2O/vE5aD9GbPwgRgGNHcrwEKcmDu0tFljqeGXYBrB93BKmSk8SmmVNhl1PKhss5WmSbvXmLSOGfDrtEP3V/0X0CgcTWlr1ZpBNdi/d9VS2oq1J/rZLxh7PsUjX8g
x-ms-exchange-antispam-messagedata: GOJic5IKNdanO653yzh44d5f0aH97ebGZus+YlYOtJOp1FhPOQ5SQuOTvCux/QCtSDJkpmosSvo+92Xw0y4lhTI7pKjkwtOJbnvu16bejfzD3eUp6I5bSNyXGMpP3UfyJQTVXgFdtZvZQsR5IR2T4fuuUWfc43Z/gx0xnZ9u/6ZwT+emPbEtKnkTRyDRjkzrY25bjBQZeHpXJxCT0Sr4rg==
x-ms-exchange-transport-forked: True
Content-Type: text/plain; charset="us-ascii"
Content-ID: <F4F6E631FE9BA0478E51D3D908A715B2@KORP216.PROD.OUTLOOK.COM>
Content-Transfer-Encoding: 8BIT
MIME-Version: 1.0
X-OriginatorOrg: outlook.com
X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-Network-Message-Id: 03e1d57e-6c06-4d45-f5d6-08d7c0559e99
X-MS-Exchange-CrossTenant-rms-persistedconsumerorg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-originalarrivaltime: 04 Mar 2020 16:03:46.9204
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Internet
X-MS-Exchange-CrossTenant-id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PU1APC01HT014
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Mar 03, 2020 at 12:29:56PM +0200, Mika Westerberg wrote:
> On Mon, Mar 02, 2020 at 03:43:02PM +0000, Nicholas Johnson wrote:
> > Return -EPERM if reg_read is NULL in bin_attr_nvmem_read() or if
> > reg_write is NULL in bin_attr_nvmem_write().
> 
> Hmm, is this patch required at all since you already check the invalid
> combinations in the patch 1/3?
This is checked in nvmem_reg_read() and nvmem_reg_write() in 
drivers/nvmem/core.c - for consistency, perhaps both should be done. 
Also, defensive programming is a good idea, because code changes might 
allow for a NULL to slip through in the future. But you are correct, at 
this moment in time, we should not be able to cause a NULL dereference 
(at least as far as I can tell).

Srinivas can either apply this patch or not, so if it is decided this is 
not needed, I will not need to do a PATCH v3. Patch 3/3 does not 
conflict with this patch.

Cheers