kallsyms: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces. The goal is to remove its use completely [2].

namebuf is eventually cleaned of any trailing llvm suffixes using
strstr(). This hints that namebuf should be NUL-terminated.

static void cleanup_symbol_name(char *s)
{
	char *res;
	...
	res = strstr(s, ".llvm.");
	...
}

Due to this, use strscpy() over strncpy() as it guarantees
NUL-termination on the destination buffer. Drop the -1 from the length
calculation as it is no longer needed to ensure NUL-termination.

Link: https://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
Link: https://github.com/KSPP/linux/issues/90 [2]
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

kernel/module/kallsyms.c

@@ -348,7 +348,7 @@ const char *module_address_lookup(unsigned long addr,
 	}
 	/* Make a copy in here where it's safe */
 	if (ret) {
-		strncpy(namebuf, ret, KSYM_NAME_LEN - 1);
+		strscpy(namebuf, ret, KSYM_NAME_LEN);
 		ret = namebuf;
 	}
 	preempt_enable();