linux-kernel - Re: [PATCH v2] mach-omap2: fixing wrong strcat for Non-NULL terminated string

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Message-ID: <20161201124015.GI23750@n2100.armlinux.org.uk>
Date:   Thu, 1 Dec 2016 12:40:15 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Maninder Singh <maninder1.s@...sung.com>
Cc:     bcousson@...libre.com, paul@...an.com, tony@...mide.com,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, ajeet.y@...sung.com,
        pankaj.m@...sung.com, Vaneet Narang <v.narang@...sung.com>
Subject: Re: [PATCH v2] mach-omap2: fixing wrong strcat for Non-NULL
 terminated string

On Thu, Dec 01, 2016 at 04:28:33PM +0530, Maninder Singh wrote:
> variable name can have Non NULL terminated string after cropping
> which may result strcat to fail, and cropping is not
> required if (strlen(oh->name) + 8 < MOD_CLK_MAX_NAME_LEN).
> 
> Issue caught with static analysis tool:
> "Dangerous usage of 'name' (strncpy doesn't always 0-terminate it)"
> 
> Signed-off-by: Vaneet Narang <v.narang@...sung.com>
> Signed-off-by: Maninder Singh <maninder1.s@...sung.com>
> ---
> v1 -> v2: changed strncpy to strlcpy
>  arch/arm/mach-omap2/omap_hwmod.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/mach-omap2/omap_hwmod.c b/arch/arm/mach-omap2/omap_hwmod.c
> index 759e1d4..582b95a 100644
> --- a/arch/arm/mach-omap2/omap_hwmod.c
> +++ b/arch/arm/mach-omap2/omap_hwmod.c
> @@ -742,12 +742,14 @@ static int _init_main_clk(struct omap_hwmod *oh)
>  	char name[MOD_CLK_MAX_NAME_LEN];
>  	struct clk *clk;
>  
> -	/* +7 magic comes from '_mod_ck' suffix */
> -	if (strlen(oh->name) + 7 > MOD_CLK_MAX_NAME_LEN)
> +	/* +8 magic comes from strlen("_mod_ck") added as suffix */
> +	if (strlen(oh->name) + 8 > MOD_CLK_MAX_NAME_LEN) {
>  		pr_warn("%s: warning: cropping name for %s\n", __func__,
>  			oh->name);
> +		strlcpy(name, oh->name, MOD_CLK_MAX_NAME_LEN - 7);
> +	} else
> +		strcpy(name, oh->name);
>  
> -	strncpy(name, oh->name, MOD_CLK_MAX_NAME_LEN - 7);
>  	strcat(name, "_mod_ck");
>  
>  	clk = clk_get(NULL, name);
> -- 
> 1.9.1
> 

Simpler, clearer, and less error-prone:

	static const char modck[] = "_mod_ck";

	if (strlen(oh->name) >= MOD_CLK_MAX_NAME_LEN - strlen(modck))
		pr_warn("%s: warning: cropping name for %s\n", __func__,
			oh->name);

	strlcpy(name, oh->name, MOD_CLK_MAX_NAME_LEN - strlen(modck));
	strlcat(name, modck, MOD_CLK_MAX_NAME_LEN);

Note that the length argument to strlcpy _includes_ the NUL terminator.
Also note the use of strlcat() which ensures that it won't overflow the
buffer.


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