[PATCH v3] x86/platform/uv: refactor deprecated strcpy and strncpy

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Both `strncpy` and `strcpy` are deprecated for use on NUL-terminated
destination strings [1].

We can see that `arg` and `uv_nmi_action` are expected to be
NUL-terminated strings due to their use within `strcmp()` and format
strings respectively.

With this in mind, a suitable replacement is `strscpy` [2] due to the
fact that it guarantees NUL-termination on its destination buffer
argument which is _not_ the case for `strncpy` or `strcpy`!

In this case, we can drop both the forced NUL-termination and the `... -1` from:
|       strncpy(arg, val, ACTION_LEN - 1);
as `strscpy` implicitly has this behavior.

Link: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings[1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@xxxxxxxxxxxxxxx
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
Changes in v3:
- Use sizeof instead of strlen (thanks Andy and Dimitri)
- Drop unrelated changes regarding strnchrnul (thanks Hans)
- Link to v2: https://lore.kernel.org/r/20230824-strncpy-arch-x86-platform-uv-uv_nmi-v2-1-e16d9a3ec570@xxxxxxxxxx

Changes in v2:
- use `sizeof` on destination string instead of `strlen` (thanks Andy, Kees and Dimitri)
- refactor code to remove potential new-line chars (thanks Yang Yang and Andy)
- Link to v1: https://lore.kernel.org/r/20230822-strncpy-arch-x86-platform-uv-uv_nmi-v1-1-931f2943de0d@xxxxxxxxxx
Note: build-tested only
 arch/x86/platform/uv/uv_nmi.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/platform/uv/uv_nmi.c b/arch/x86/platform/uv/uv_nmi.c
index a60af0230e27..dd30fb2baf6c 100644
--- a/arch/x86/platform/uv/uv_nmi.c
+++ b/arch/x86/platform/uv/uv_nmi.c
@@ -205,8 +205,7 @@ static int param_set_action(const char *val, const struct kernel_param *kp)
 	char arg[ACTION_LEN], *p;
 	/* (remove possible '\n') */
-	strncpy(arg, val, ACTION_LEN - 1);
-	arg[ACTION_LEN - 1] = '\0';
+	strscpy(arg, val, sizeof(arg));
 	p = strchr(arg, '\n');
 	if (p)
 		*p = '\0';
@@ -216,7 +215,7 @@ static int param_set_action(const char *val, const struct kernel_param *kp)
 	if (i < n) {
-		strcpy(uv_nmi_action, arg);
+		strscpy(uv_nmi_action, arg, sizeof(uv_nmi_action));
 		pr_info("UV: New NMI action:%s\n", uv_nmi_action);
 		return 0;
@@ -959,7 +958,7 @@ static int uv_handle_nmi(unsigned int reason, struct pt_regs *regs)
 		/* Unexpected return, revert action to "dump" */
 		if (master)
-			strncpy(uv_nmi_action, "dump", strlen(uv_nmi_action));
+			strscpy(uv_nmi_action, "dump", sizeof(uv_nmi_action));
 	/* Pause as all CPU's enter the NMI handler */

base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
change-id: 20230822-strncpy-arch-x86-platform-uv-uv_nmi-474e5295c2c1

Best regards,
Justin Stitt <justinstitt@xxxxxxxxxx>

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