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
Vasily Averin (7):
pstore_ftrace_seq_next should increase position index
gcov_seq_next should increase position index
t_next should increase position index
fpid_next should increase position index
eval_map_next should increase position index
trigger_next should increase position index
sysvipc_find_ipc should increase position index
fs/pstore/inode.c | 2 +-
ipc/util.c | 2 +-
kernel/gcov/fs.c | 2 +-
kernel/trace/ftrace.c | 9 ++++++---
kernel/trace/trace.c | 4 +---
kernel/trace/trace_events_trigger.c | 5 +++--
6 files changed, 13 insertions(+), 11 deletions(-)
--
1.8.3.1
It helps to detect missed or out-of-tree incorect .next seq_file functions
https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <[email protected]>
---
fs/seq_file.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 1600034..07c6909 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -256,9 +256,12 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
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;
--
1.8.3.1
On Fri, 24 Jan 2020 10:02:36 +0300
Vasily Averin <[email protected]> wrote:
>
> 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
Since you sent the patches out individually, and not as the usually way
of replying to the 0/7 patch (this email), do you expect the patches to
just be accepted by the individual maintainers, and not as a series?
-- Steve
>
> https://bugzilla.kernel.org/show_bug.cgi?id=206283
>
> Vasily Averin (7):
> pstore_ftrace_seq_next should increase position index
> gcov_seq_next should increase position index
> t_next should increase position index
> fpid_next should increase position index
> eval_map_next should increase position index
> trigger_next should increase position index
> sysvipc_find_ipc should increase position index
>
> fs/pstore/inode.c | 2 +-
> ipc/util.c | 2 +-
> kernel/gcov/fs.c | 2 +-
> kernel/trace/ftrace.c | 9 ++++++---
> kernel/trace/trace.c | 4 +---
> kernel/trace/trace_events_trigger.c | 5 +++--
> 6 files changed, 13 insertions(+), 11 deletions(-)
>
On 1/24/20 6:50 PM, Steven Rostedt wrote:
> On Fri, 24 Jan 2020 10:02:36 +0300
> Vasily Averin <[email protected]> wrote:
>
>>
>> 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
>
> Since you sent the patches out individually, and not as the usually way
> of replying to the 0/7 patch (this email), do you expect the patches to
> just be accepted by the individual maintainers, and not as a series?
Yes, you are right, I've missed it.
Could you please review tracing-related patches of this patch set?
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=206283
>>
>> Vasily Averin (7):
>> pstore_ftrace_seq_next should increase position index
>> gcov_seq_next should increase position index
>> t_next should increase position index
>> fpid_next should increase position index
>> eval_map_next should increase position index
>> trigger_next should increase position index
>> sysvipc_find_ipc should increase position index
>>
>> fs/pstore/inode.c | 2 +-
>> ipc/util.c | 2 +-
>> kernel/gcov/fs.c | 2 +-
>> kernel/trace/ftrace.c | 9 ++++++---
>> kernel/trace/trace.c | 4 +---
>> kernel/trace/trace_events_trigger.c | 5 +++--
>> 6 files changed, 13 insertions(+), 11 deletions(-)
>>
>