2016-12-01 11:03:39

by Maninder Singh

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

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 <[email protected]>
Signed-off-by: Maninder Singh <[email protected]>
---
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

2016-12-01 12:40:46

by Russell King (Oracle)

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 <[email protected]>
> Signed-off-by: Maninder Singh <[email protected]>
> ---
> 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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