The patch titled
Subject: fs/seq_file.c: seq_read(): add info message about buggy .next functions
has been added to the -mm tree. Its filename is
seq_read-info-message-about-buggy-next-functions.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/seq_read-info-message-about-buggy-next-functions.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/seq_read-info-message-about-buggy-next-functions.patch
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From: Vasily Averin <vvs@xxxxxxxxxxxxx>
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.
https://bugzilla.kernel.org/show_bug.cgi?id=206283
Link: http://lkml.kernel.org/r/244674e5-760c-86bd-d08a-047042881748@xxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/7c24087c-e280-e580-5b0c-0cdaeb14cd18@xxxxxxxxxxxxx
Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
Cc: NeilBrown <neilb@xxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/seq_file.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
--- a/fs/seq_file.c~seq_read-info-message-about-buggy-next-functions
+++ a/fs/seq_file.c
@@ -256,9 +256,12 @@ 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("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;
_
Patches currently in -mm which might be from vvs@xxxxxxxxxxxxx are
seq_read-info-message-about-buggy-next-functions.patch
pstore_ftrace_seq_next-should-increase-position-index.patch
gcov_seq_next-should-increase-position-index.patch
sysvipc_find_ipc-should-increase-position-index.patch
