linux-kernel - Re: [PATCH] net: hisilicon: Fix usage of uninitialized variable in function mdio_sc_cfg_reg

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Message-Id: <20191002.142214.252882219207569928.davem@davemloft.net>
Date:   Wed, 02 Oct 2019 14:22:14 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     yzhai003@....edu
Cc:     csong@...ucr.edu, zhiyunq@...ucr.edu, yisen.zhuang@...wei.com,
        salil.mehta@...wei.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: hisilicon: Fix usage of uninitialized variable in
 function mdio_sc_cfg_reg_write()

From: Yizhuo <yzhai003@....edu>
Date: Tue,  1 Oct 2019 13:24:39 -0700

> In function mdio_sc_cfg_reg_write(), variable "reg_value" could be
> uninitialized if regmap_read() fails. However, "reg_value" is used
> to decide the control flow later in the if statement, which is
> potentially unsafe.
> 
> Signed-off-by: Yizhuo <yzhai003@....edu>

Applied, but really this is such a pervasive problem.

So much code doesn't check the return value from either regmap_read
or regmap_write.

_EVEN_ in the code you are editing, the patch context shows an unchecked
regmap_write() call.

> @@ -148,11 +148,15 @@ static int mdio_sc_cfg_reg_write(struct hns_mdio_device *mdio_dev,
>  {
>  	u32 time_cnt;
>  	u32 reg_value;
> +	int ret;
>  
>  	regmap_write(mdio_dev->subctrl_vbase, cfg_reg, set_val);
        ^^^^^^^^^^^^

Grepping for regmap_{read,write}() shows how big an issue this is.

I don't know what to do, maybe we can work over time to add checks to
all calls and then force warnings on unchecked return values so that
the problem is not introduced in the future.