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

[Greg Kroah-Hartman]

From: Vasily Averin <vvs@xxxxxxxxxxxxx>

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@xxxxxxxxxx
Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Link: https://lore.kernel.org/r/d13805e5-695e-8ac3-b678-26ca2313629f@xxxxxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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;
 }