linux-kernel - [PATCH 4.19 105/195] jbd2_seq_info_next should increase position index

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Message-Id: <20200210122315.590513717@linuxfoundation.org>
Date:   Mon, 10 Feb 2020 04:32:43 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, stable@...nel.org,
        Vasily Averin <vvs@...tuozzo.com>, Jan Kara <jack@...e.cz>,
        Theodore Tso <tytso@....edu>
Subject: [PATCH 4.19 105/195] jbd2_seq_info_next should increase position index

From: Vasily Averin <vvs@...tuozzo.com>

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@...nel.org
Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Link: https://lore.kernel.org/r/d13805e5-695e-8ac3-b678-26ca2313629f@virtuozzo.com
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/jbd2/journal.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1002,6 +1002,7 @@ static void *jbd2_seq_info_start(struct
 
 static void *jbd2_seq_info_next(struct seq_file *seq, void *v, loff_t *pos)
 {
+	(*pos)++;
 	return NULL;
 }