linux-hardening - Re: [PATCH v3 7/7] staging: ks7010: Avoid clashing function prototypes

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Date:   Wed, 9 Nov 2022 16:10:52 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3 7/7] staging: ks7010: Avoid clashing function
 prototypes

On Tue, Nov 08, 2022 at 02:34:46PM -0600, 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 27 warnings like these:
> 
> drivers/staging/ks7010/ks_wlan_net.c:2415:2: warning: cast from 'int (*)(struct net_device *, struct iw_request_info *, struct iw_point *, 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)ks_wlan_get_firmware_version,/* 3 KS_WLAN_GET_FIRM_VERSION */
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The ks_wlan_net 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.
> 
> These changes were made partly manually and partly with the help of
> Coccinelle.
> 
> Link: https://reviews.llvm.org/D134831 [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

The "mode" churn makes this a bit harder to review, but I think the
final result looks better.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook