um: Fix incorrect assumptions about max pid length

pids are no longer limited to 16-bits, bump to 32-bits,
ie. 9 decimal characters.  Additionally sizeof("/") already
returns 2 - ie. it already accounts for trailing zero.

Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Linux UM Mailing List <linux-um@lists.infradead.org>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/os-Linux/umid.c

@@ -97,7 +97,7 @@ static int remove_files_and_dir(char *dir)
 	while ((ent = readdir(directory)) != NULL) {
 		if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
 			continue;
-		len = strlen(dir) + sizeof("/") + strlen(ent->d_name) + 1;
+		len = strlen(dir) + strlen("/") + strlen(ent->d_name) + 1;
 		if (len > sizeof(file)) {
 			ret = -E2BIG;
 			goto out;
@@ -135,7 +135,7 @@ static int remove_files_and_dir(char *dir)
  */
 static inline int is_umdir_used(char *dir)
 {
-	char pid[sizeof("nnnnn\0")], *end, *file;
+	char pid[sizeof("nnnnnnnnn")], *end, *file;
 	int dead, fd, p, n, err;
 	size_t filelen;
 
@@ -217,10 +217,10 @@ static int umdir_take_if_dead(char *dir)
 
 static void __init create_pid_file(void)
 {
-	char pid[sizeof("nnnnn\0")], *file;
+	char pid[sizeof("nnnnnnnnn")], *file;
 	int fd, n;
 
-	n = strlen(uml_dir) + UMID_LEN + sizeof("/pid\0");
+	n = strlen(uml_dir) + UMID_LEN + sizeof("/pid");
 	file = malloc(n);
 	if (!file)
 		return;