From: Vasily Averin <vvs@virtuozzo.com>
Date: Thu, 23 Jan 2020 09:05:10 +0000 (+0300)
Subject: jbd2_seq_info_next should increase position index
X-Git-Tag: v4.19.103~91
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=68e81e14ddb897d5392cb4967ac398b52435adea;p=thirdparty%2Fkernel%2Fstable.git

jbd2_seq_info_next should increase position index

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>
---

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index df390a69c49a8..1a2339f2cb49b 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1002,6 +1002,7 @@ 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;
 }