linux-kernel - Re: [PATCH v2 2/6] hostap: Avoid clashing function prototypes

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Message-ID: <202210290025.15F3F949B9@keescook>
Date:   Sat, 29 Oct 2022 00:26:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Jouni Malinen <j@...fi>, Kalle Valo <kvalo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 2/6] hostap: Avoid clashing function prototypes

On Thu, Oct 27, 2022 at 03:18:37PM -0500, Gustavo A. R. Silva wrote:
> When built with Control Flow Integrity, function prototypes between
> caller and function declaration must match. These mismatches are visible
> at compile time with the new -Wcast-function-type-strict in Clang[1].
> 
> Fix a total of 42 warnings like these:
> 
> ../drivers/net/wireless/intersil/hostap/hostap_ioctl.c:3868:2: warning: cast from 'int (*)(struct net_device *, struct iw_request_info *, char *, char *)' to 'iw_handler' (aka 'int (*)(struct net_device *, struct iw_request_info *, union iwreq_data *, char *)') converts to incompatible function type [-Wcast-function-type-strict]
>         (iw_handler) prism2_get_name,                   /* SIOCGIWNAME */
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The hostap Wireless Extension handler callbacks (iw_handler) use a
> union for the data argument. Actually use the union and perform explicit
> member selection in the function body instead of having a function
> prototype mismatch. There are no resulting binary differences
> before/after changes.
> 
> Link: https://github.com/KSPP/linux/issues/235
> Link: https://reviews.llvm.org/D134831 [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Looks like prism2_private_handler contents could be uncast? Otherwise,
yeah, looks good.

-- 
Kees Cook