linux-kernel - Re: [PATCH v3 3/9] brcmfmac: firmware: Do not crash on a NULL board

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Date:   Thu, 20 Jan 2022 15:13:11 +0900
From:   Hector Martin <marcan@...can.st>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Arend van Spriel <aspriel@...il.com>,
        Franky Lin <franky.lin@...adcom.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Chi-hsien Lin <chi-hsien.lin@...ineon.com>,
        Wright Feng <wright.feng@...ineon.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Mark Kettenis <kettenis@...nbsd.org>,
        Rafał Miłecki <zajec5@...il.com>,
        Pieter-Paul Giesberts <pieter-paul.giesberts@...adcom.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Hans de Goede <hdegoede@...hat.com>,
        "John W. Linville" <linville@...driver.com>,
        "brian m. carlson" <sandals@...stytoothpaste.net>,
        "open list:TI WILINK WIRELES..." <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "open list:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER" 
        <brcm80211-dev-list.pdl@...adcom.com>,
        SHA-cyfmac-dev-list@...ineon.com
Subject: Re: [PATCH v3 3/9] brcmfmac: firmware: Do not crash on a NULL
 board_type

On 20/01/2022 06.45, Andy Shevchenko wrote:
> On Mon, Jan 17, 2022 at 4:30 PM Hector Martin <marcan@...can.st> wrote:
>>
>> This unbreaks support for USB devices, which do not have a board_type
>> to create an alt_path out of and thus were running into a NULL
>> dereference.
> 
> In v5.16 we have two call sites:
> 
> 1.
>   if (cur->type == BRCMF_FW_TYPE_NVRAM && fwctx->req->board_type) {
>     ...
>     alt_path = brcm_alt_fw_path(cur->path, fwctx->req->board_type);
> 
> 2.
>   alt_path = brcm_alt_fw_path(first->path, fwctx->req->board_type);
>   if (alt_path) {
>     ...
> 
> Looking at them I would rather expect to see (as a quick fix, the
> better solution is to unify those call sites by splitting out a common
> helper):
> 
>   if (fwctx->req->board_type) {
>     alt_path = brcm_alt_fw_path(first->path, fwctx->req->board_type);
>   else
>     alt_path = NULL;
>    ...
> 

Since brcm_alt_fw_path can fail anyway, and its return value is already
NULL-checked, it makes sense to propagate the NULL board_path there
rather than doing it at all the callsites. That's a common pattern, e.g.
the entire DT API is designed to accept NULL nodes. That does mean that
the first callsite has a redundant NULL check, yes, but that doesn't hurt.

This is all going to change with subsequent patches anyway; the point of
this patch is just to fix the regression.

-- 
Hector Martin (marcan@...can.st)
Public Key: https://mrcn.st/pub