From 49f0705ec89358c6f67d153a0bf5f31e6b10c371 Mon Sep 17 00:00:00 2001
From: Vasily Averin <vvs@virtuozzo.com>
Date: Thu, 23 Jan 2020 12:05:10 +0300
Subject: [PATCH] jbd2_seq_info_next should increase position index

task #28557737

commit 1a8e9cf40c9a6a2e40b1e924b13ed303aeea4418 upstream.

if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.

Script below generates endless output
 $ q=;while read -r r;do echo "$((++q)) $r";done </proc/fs/jbd2/DEV/info

https://bugzilla.kernel.org/show_bug.cgi?id=206283

Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface")
Cc: stable@kernel.org
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/d13805e5-695e-8ac3-b678-26ca2313629f@virtuozzo.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Acked-by: Joseph Qi <joseph.qi@linux.alibaba.com>
---
 fs/jbd2/journal.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index f522bf45ec71..1a4eb1464db4 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1057,6 +1057,7 @@ static void *jbd2_seq_info_start(struct seq_file *seq, loff_t *pos)
 
 static void *jbd2_seq_info_next(struct seq_file *seq, void *v, loff_t *pos)
 {
+	(*pos)++;
 	return NULL;
 }
 
-- 
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