seq_file: always clear m->count when we free m->buf

commit 801a7605 upstream.

Once we'd freed m->buf, m->count should become zero - we have no valid
contents reachable via m->buf.
Reported-by: Charley (Hao Chuan) Chu <charley.chu@broadcom.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

fs/seq_file.c

@@ -136,6 +136,7 @@ static int traverse(struct seq_file *m, loff_t offset)
 Eoverflow:
 	m->op->stop(m, p);
 	kfree(m->buf);
+	m->count = 0;
 	m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
 	return !m->buf ? -ENOMEM : -EAGAIN;
 }
@@ -232,10 +233,10 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 			goto Fill;
 		m->op->stop(m, p);
 		kfree(m->buf);
+		m->count = 0;
 		m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
 		if (!m->buf)
 			goto Enomem;
-		m->count = 0;
 		m->version = 0;
 		pos = m->index;
 		p = m->op->start(m, &pos);