linux-kernel - Re: [PATCH] mwifiex: remove function pointer check

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Message-ID: <20200908042112.GA111690@ubuntu-n2-xlarge-x86>
Date:   Mon, 7 Sep 2020 21:21:12 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     trix@...hat.com
Cc:     amitkarwar@...il.com, ganapathi.bhat@....com,
        huxinming820@...il.com, kvalo@...eaurora.org, davem@...emloft.net,
        kuba@...nel.org, ndesaulniers@...gle.com, bzhao@...vell.com,
        dkiran@...vell.com, frankh@...vell.com, linville@...driver.com,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] mwifiex: remove function pointer check

On Sun, Sep 06, 2020 at 01:05:48PM -0700, trix@...hat.com wrote:
> From: Tom Rix <trix@...hat.com>
> 
> clang static analyzer reports this problem
> 
> init.c:739:8: warning: Called function pointer
>   is null (null dereference)
>         ret = adapter->if_ops.check_fw_status( ...
>               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> In mwifiex_dnld_fw, there is an earlier check for check_fw_status(),
> The check was introduced for usb support at the same time this
> check in _mwifiex_fw_dpc() was made
> 
> 	if (adapter->if_ops.dnld_fw) {
> 		ret = adapter->if_ops.dnld_fw(adapter, &fw);
> 	} else {
> 		ret = mwifiex_dnld_fw(adapter, &fw);
> 	}
> 
> And a dnld_fw function initialized as part the usb's
> mwifiex_if_ops.
> 
> The other instances of mwifiex_if_ops for pci and sdio
> both set check_fw_status.
> 
> So the first check is not needed and can be removed.
> 
> Fixes: 4daffe354366 ("mwifiex: add support for Marvell USB8797 chipset")
> Signed-off-by: Tom Rix <trix@...hat.com>

Indeed, on the surface, mwifiex_dnld_fw assumes that check_fw_status()
cannot be NULL because it will always be called at the end of the
function even if the first check is skipped.

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

> ---
>  drivers/net/wireless/marvell/mwifiex/init.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/wireless/marvell/mwifiex/init.c b/drivers/net/wireless/marvell/mwifiex/init.c
> index 82d69bc3aaaf..f006a3d72b40 100644
> --- a/drivers/net/wireless/marvell/mwifiex/init.c
> +++ b/drivers/net/wireless/marvell/mwifiex/init.c
> @@ -695,14 +695,12 @@ int mwifiex_dnld_fw(struct mwifiex_adapter *adapter,
>  	int ret;
>  	u32 poll_num = 1;
>  
> -	if (adapter->if_ops.check_fw_status) {
> -		/* check if firmware is already running */
> -		ret = adapter->if_ops.check_fw_status(adapter, poll_num);
> -		if (!ret) {
> -			mwifiex_dbg(adapter, MSG,
> -				    "WLAN FW already running! Skip FW dnld\n");
> -			return 0;
> -		}
> +	/* check if firmware is already running */
> +	ret = adapter->if_ops.check_fw_status(adapter, poll_num);
> +	if (!ret) {
> +		mwifiex_dbg(adapter, MSG,
> +			    "WLAN FW already running! Skip FW dnld\n");
> +		return 0;
>  	}
>  
>  	/* check if we are the winner for downloading FW */
> -- 
> 2.18.1
> 
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