[PATCH linux-next v3] x86/platform/uv: use strscpy to instead of strncpy()

[PATCH linux-next v3] x86/platform/uv: use strscpy to instead of strncpy()

[yang.yang29]

From: Xu Panda <xu.panda@zte.com.cn>

The implementation of strscpy() is more robust and safer.
That's now the recommended way to copy NUL terminated strings.

Signed-off-by: Xu Panda <xu.panda@zte.com.cn>
Signed-off-by: Yang Yang <yang.yang29@zte.com>
---
change for v3
 - remove the remaining definition of p, and fix the mistake
which leads to eating one character. Thanks to Andy Shevchenko again.
---
 arch/x86/platform/uv/uv_nmi.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/platform/uv/uv_nmi.c b/arch/x86/platform/uv/uv_nmi.c
index a60af0230e27..a55550b779e1 100644
--- a/arch/x86/platform/uv/uv_nmi.c
+++ b/arch/x86/platform/uv/uv_nmi.c
@@ -202,14 +202,10 @@ static int param_set_action(const char *val, const struct kernel_param *kp)
 {
 	int i;
 	int n = ARRAY_SIZE(valid_acts);
-	char arg[ACTION_LEN], *p;
+	char arg[ACTION_LEN];

 	/* (remove possible '\n') */
-	strncpy(arg, val, ACTION_LEN - 1);
-	arg[ACTION_LEN - 1] = '\0';
-	p = strchr(arg, '\n');
-	if (p)
-		*p = '\0';
+	strscpy(arg, val, strnchrnul(val, ACTION_LEN - 1, '\n') - val + 1);

 	for (i = 0; i < n; i++)
 		if (!strcmp(arg, valid_acts[i].action))
-- 
2.15.2

Re: [PATCH linux-next v3] x86/platform/uv: use strscpy to instead of strncpy()

[Andy Shevchenko]

On Fri, Dec 9, 2022 at 9:45 AM <yang.yang29@zte.com.cn> wrote:
>
> From: Xu Panda <xu.panda@zte.com.cn>
>
> The implementation of strscpy() is more robust and safer.
> That's now the recommended way to copy NUL terminated strings.

...

> +       strscpy(arg, val, strnchrnul(val, ACTION_LEN - 1, '\n') - val + 1);

Instead of  -1 +1 you should simply use the sizeof(arg) as I mentioned.

       strscpy(arg, val, strnchrnul(val, sizeof(arg), '\n') - val);

The returned pointer by strnchrnul() either points to the '\n' or to
'\0' and when we subtract pointer to the start we will get the exact
length of the string. In case it equals ACTION_LEN the last character
will be replaced by '\0'.

Where am I mistaken?

-- 
With Best Regards,
Andy Shevchenko