From: Miklos Szeredi <mszeredi@redhat.com>
Date: Wed, 15 Nov 2017 10:34:58 +0000 (+0100)
Subject: seq_file: fix incomplete reset on read from zero offset
X-Git-Tag: v4.16-rc1~13^2
X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=cf5eebae2cd28d37581507668605f4d23cd7218d;p=uclinux-h8%2Flinux.git

seq_file: fix incomplete reset on read from zero offset

When resetting iterator on a zero offset we need to discard any data
already in the buffer (count), and private state of the iterator (version).

For example this bug results in first line being repeated in /proc/mounts
if doing a zero size read before a non-zero size read.

Reported-by: Rich Felker <dalias@libc.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: e522751d605d ("seq_file: reset iterator to first record for zero offset")
Cc: <stable@vger.kernel.org> # v4.10
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 4be761c1a03d..eea09f6d8830 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -181,8 +181,11 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 	 * if request is to read from zero offset, reset iterator to first
 	 * record as it might have been already advanced by previous requests
 	 */
-	if (*ppos == 0)
+	if (*ppos == 0) {
 		m->index = 0;
+		m->version = 0;
+		m->count = 0;
+	}
 
 	/* Don't assume *ppos is where we left it */
 	if (unlikely(*ppos != m->read_pos)) {