[PATCH 5.5 192/367] jbd2_seq_info_next should increase position index

Greg Kroah-Hartman
2020-02-10T12:45:00Z

From: Vasily Averin <vvs@virtuozzo.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@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>

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

--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -982,6 +982,7 @@ 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;
}