selinuxfs: use scnprintf to get real length for inode

The return value of snprintf maybe over the size of TMPBUFLEN, use
scnprintf instead in sel_read_class and sel_read_perm.

Signed-off-by: liuyang34 <liuyang34@xiaomi.com>
[PM: cleaned up the description]
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/selinuxfs.c

@@ -1728,7 +1728,7 @@ static ssize_t sel_read_class(struct file *file, char __user *buf,
 {
 	unsigned long ino = file_inode(file)->i_ino;
 	char res[TMPBUFLEN];
-	ssize_t len = snprintf(res, sizeof(res), "%d", sel_ino_to_class(ino));
+	ssize_t len = scnprintf(res, sizeof(res), "%d", sel_ino_to_class(ino));
 	return simple_read_from_buffer(buf, count, ppos, res, len);
 }
 
@@ -1742,7 +1742,7 @@ static ssize_t sel_read_perm(struct file *file, char __user *buf,
 {
 	unsigned long ino = file_inode(file)->i_ino;
 	char res[TMPBUFLEN];
-	ssize_t len = snprintf(res, sizeof(res), "%d", sel_ino_to_perm(ino));
+	ssize_t len = scnprintf(res, sizeof(res), "%d", sel_ino_to_perm(ino));
 	return simple_read_from_buffer(buf, count, ppos, res, len);
 }