From 3bfa7e141b0bbb818b25e0daafb65aee92e49ac4 Mon Sep 17 00:00:00 2001 From: Vasily Averin Date: Fri, 10 Apr 2020 14:34:06 -0700 Subject: fs/seq_file.c: seq_read(): add info message about buggy .next functions Patch series "seq_file .next functions should increase position index". In Aug 2018 NeilBrown noticed commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface") "Some ->next functions do not increment *pos when they return NULL... Note that such ->next functions are buggy and should be fixed. A simple demonstration is dd if=/proc/swaps bs=1000 skip=1 Choose any block size larger than the size of /proc/swaps. This will always show the whole last line of /proc/swaps" Described problem is still actual. If you make lseek into middle of last output line following read will output end of last line and whole last line once again. $ dd if=/proc/swaps bs=1 # usual output Filename Type Size Used Priority /dev/dm-0 partition 4194812 97536 -2 104+0 records in 104+0 records out 104 bytes copied $ dd if=/proc/swaps bs=40 skip=1 # last line was generated twice dd: /proc/swaps: cannot skip to specified offset v/dm-0 partition 4194812 97536 -2 /dev/dm-0 partition 4194812 97536 -2 3+1 records in 3+1 records out 131 bytes copied There are lot of other affected files, I've found 30+ including /proc/net/ip_tables_matches and /proc/sysvipc/* I've sent patches into maillists of affected subsystems already, this patch-set fixes the problem in files related to pstore, tracing, gcov, sysvipc and other subsystems processed via linux-kernel@ mailing list directly https://bugzilla.kernel.org/show_bug.cgi?id=206283 This patch (of 4): Add debug code to seq_read() to detect missed or out-of-tree incorrect .next seq_file functions. [akpm@linux-foundation.org: s/pr_info/pr_info_ratelimited/, per Qian Cai] https://bugzilla.kernel.org/show_bug.cgi?id=206283 Signed-off-by: Vasily Averin Signed-off-by: Andrew Morton Cc: NeilBrown Cc: Al Viro Cc: Steven Rostedt Cc: Davidlohr Bueso Cc: Ingo Molnar Cc: Manfred Spraul Cc: Peter Oberparleiter Cc: Waiman Long Link: http://lkml.kernel.org/r/244674e5-760c-86bd-d08a-047042881748@virtuozzo.com Link: http://lkml.kernel.org/r/7c24087c-e280-e580-5b0c-0cdaeb14cd18@virtuozzo.com Signed-off-by: Linus Torvalds --- fs/seq_file.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'fs/seq_file.c') diff --git a/fs/seq_file.c b/fs/seq_file.c index 79781ebd2145..70f5fdf99bf6 100644 --- a/fs/seq_file.c +++ b/fs/seq_file.c @@ -232,9 +232,12 @@ Fill: loff_t pos = m->index; p = m->op->next(m, p, &m->index); - if (pos == m->index) - /* Buggy ->next function */ + if (pos == m->index) { + pr_info_ratelimited("buggy seq_file .next function %ps " + "did not updated position index\n", + m->op->next); m->index++; + } if (!p || IS_ERR(p)) { err = PTR_ERR(p); break; -- cgit