linux-kernel - Re: [PATCH v3 2/7] cfg80211: Avoid clashing function prototypes

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Date:   Wed, 9 Nov 2022 16:06:58 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Stanislav Yakovlev <stas.yakovlev@...il.com>,
        Johannes Berg <johannes@...solutions.net>,
        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 v3 2/7] cfg80211: Avoid clashing function prototypes

On Tue, Nov 08, 2022 at 02:23:55PM -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 73 warnings like these:
> 
> drivers/net/wireless/intersil/orinoco/wext.c:1379:27: warning: cast from 'int (*)(struct net_device *, struct iw_request_info *, struct iw_param *, 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(SIOCGIWPOWER,        (iw_handler)orinoco_ioctl_getpower),
>                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> ../net/wireless/wext-compat.c:1607:33: 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_IOCTL_IDX(SIOCSIWGENIE)]    = (iw_handler) cfg80211_wext_siwgenie,
>                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> ../drivers/net/wireless/intersil/orinoco/wext.c:1390:27: error: incompatible function pointer types initializing 'const iw_handler' (aka 'int (*const)(struct net_device *, struct iw_request_info *, union iwreq_data *, char *)') with an expression of type 'int (struct net_device *, struct iw_request_info *, struct iw_param *, char *)' [-Wincompatible-function-pointer-types]
>         IW_HANDLER(SIOCGIWRETRY,        cfg80211_wext_giwretry),
>                                         ^~~~~~~~~~~~~~~~~~~~~~
> 
> The cfg80211 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://github.com/KSPP/linux/issues/234
> Link: https://reviews.llvm.org/D134831 [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

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

-- 
Kees Cook