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

[Russell King - ARM Linux]

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 
> Signed-off-by: Maninder Singh 
> ---
> 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.


-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
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Re: [PATCH v2] mach-omap2: fixing wrong strcat for Non-NULL terminated string

[Russell King - ARM Linux]

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 
> Signed-off-by: Maninder Singh 
> ---
> 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.


-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.