diff options
author | Vasily Averin <vvs@virtuozzo.com> | 2020-04-10 14:34:06 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-04-10 15:36:22 -0700 |
commit | 3bfa7e141b0bbb818b25e0daafb65aee92e49ac4 (patch) | |
tree | 3dc8c16fe3634a8a0e40e1e3039cf3a24c62f609 /fs | |
parent | cb8d9937e85559ea0ad1f4f83df8ad1288fed47d (diff) |
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 <vvs@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: NeilBrown <neilb@suse.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
Cc: Waiman Long <longman@redhat.com>
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 <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/seq_file.c | 7 |
1 files changed, 5 insertions, 2 deletions
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; |