apparmor: Replace memcpy + NUL termination with kmemdup_nul in do_setattr

Use kmemdup_nul() to copy 'value' instead of using memcpy() followed by
a manual NUL termination.  No functional changes.

Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/lsm.c

@@ -856,12 +856,9 @@ static int do_setattr(u64 attr, void *value, size_t size)
 
 	/* AppArmor requires that the buffer must be null terminated atm */
 	if (args[size - 1] != '\0') {
-		/* null terminate */
-		largs = args = kmalloc(size + 1, GFP_KERNEL);
+		largs = args = kmemdup_nul(value, size, GFP_KERNEL);
 		if (!args)
 			return -ENOMEM;
-		memcpy(args, value, size);
-		args[size] = '\0';
 	}
 
 	error = -EINVAL;