linux-kernel - Re: [PATCH v2 1/2] mtd: nand: Error out if cmd

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Date:	Wed, 20 Jul 2016 08:44:03 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Andrey Smirnov <andrew.smirnov@...il.com>
Cc:	linux-mtd@...ts.infradead.org, Richard Weinberger <richard@....at>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mtd: nand: Error out if cmd_ctrl() is missing

On Tue, 19 Jul 2016 22:33:57 -0700
Andrey Smirnov <andrew.smirnov@...il.com> wrote:

> If no user specified chip->select_chip() function is provided, code in
> nand_base.c will automatically set this hook to nand_select_chip(),
> which in turn depends on chip->cmd_ctrl() hook being valid. Not
> providing both of those functions in NAND controller driver (for example
> by mistake) will result in a bit cryptic segfault. Same is true for
> chip->cmdfunc().
> 
> To avoid the above scenario change the prototype of nand_set_defaults()
> to return error code, all the callers to check for it and error out if
> cmd_ctrl() is not provided.
> 
> Suggested-by: Brian Norris <computersforpeace@...il.com>
> Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> ---
>  drivers/mtd/nand/nand_base.c | 29 ++++++++++++++++++++++++-----
>  1 file changed, 24 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index ce7b2ca..bee480f 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -3114,22 +3114,30 @@ static void nand_shutdown(struct mtd_info *mtd)
>  }
>  
>  /* Set default functions */
> -static void nand_set_defaults(struct nand_chip *chip, int busw)
> +static int nand_set_defaults(struct nand_chip *chip, int busw)
>  {
>  	/* check for proper chip_delay setup, set 20us if not */
>  	if (!chip->chip_delay)
>  		chip->chip_delay = 20;
>  
>  	/* check, if a user supplied command function given */
> -	if (chip->cmdfunc == NULL)
> +	if (chip->cmdfunc == NULL) {
> +		if (!chip->cmd_ctrl)
> +			goto no_cmd_ctrl;
> +
>  		chip->cmdfunc = nand_command;
> +	}
>  
>  	/* check, if a user supplied wait function given */
>  	if (chip->waitfunc == NULL)
>  		chip->waitfunc = nand_wait;
>  
> -	if (!chip->select_chip)
> +	if (!chip->select_chip) {
> +		if (!chip->cmd_ctrl)
> +			goto no_cmd_ctrl;
> +
>  		chip->select_chip = nand_select_chip;
> +	}
>  
>  	/* set for ONFI nand */
>  	if (!chip->onfi_set_features)
> @@ -3161,6 +3169,11 @@ static void nand_set_defaults(struct nand_chip *chip, int busw)
>  		init_waitqueue_head(&chip->controller->wq);
>  	}
>  
> +	return 0;
> +
> +no_cmd_ctrl:
> +	pr_err("chip.cmd_ctrl() callback is not provided\n");
> +	return -EINVAL;
>  }
>  
>  /* Sanitize ONFI strings so we can safely print them */
> @@ -3878,9 +3891,13 @@ ident_done:
>  	}
>  
>  	if (chip->options & NAND_BUSWIDTH_AUTO) {
> +		int ret;
> +
>  		WARN_ON(chip->options & NAND_BUSWIDTH_16);
>  		chip->options |= busw;
> -		nand_set_defaults(chip, busw);
> +		ret = nand_set_defaults(chip, busw);

I realize this one will actually never fail because it has already been
checked in nand_scan_ident(). Maybe we should leave the
nand_set_defaults() as a void function and check for missing
->cmd_ctrl() directly in nand_scan_ident().

> +		if (ret < 0)
> +			return ERR_PTR(ret);
>  	} else if (busw != (chip->options & NAND_BUSWIDTH_16)) {
>  		/*
>  		 * Check, if buswidth is correct. Hardware drivers should set
> @@ -3998,7 +4015,9 @@ int nand_scan_ident(struct mtd_info *mtd, int maxchips,
>  		mtd->name = dev_name(mtd->dev.parent);
>  
>  	/* Set the default functions */
> -	nand_set_defaults(chip, chip->options & NAND_BUSWIDTH_16);
> +	ret = nand_set_defaults(chip, chip->options & NAND_BUSWIDTH_16);
> +	if (ret < 0)
> +		return ret;
>  
>  	/* Read the flash type */
>  	type = nand_get_flash_type(mtd, chip, &nand_maf_id,