[PATCH 0/1] s390: seq_file .next functions should increase position index

[PATCH 0/1] s390: seq_file .next functions should increase position index

[Vasily Averin]

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/*

Following patch fixes s390-related file

https://bugzilla.kernel.org/show_bug.cgi?id=206283

Vasily Averin (1):
  cio_ignore_proc_seq_next should increase position index

 drivers/s390/cio/blacklist.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

-- 
1.8.3.1

Re: [PATCH 0/1] s390: seq_file .next functions should increase position index

[Christian Borntraeger]

I only got your cover letter, but not the patch itself. Can you resend?


On 24.01.20 06:48, Vasily Averin wrote:
> 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/*
> 
> Following patch fixes s390-related file
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=206283
> 
> Vasily Averin (1):
>   cio_ignore_proc_seq_next should increase position index
> 
>  drivers/s390/cio/blacklist.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 

Re: [PATCH 0/1] s390: seq_file .next functions should increase position index

[Vasily Averin]

On 2/5/20 10:55 PM, Christian Borntraeger wrote:
> I only got your cover letter, but not the patch itself. Can you resend?

Patch itself had another subject:
"[PATCH 1/1] cio_ignore_proc_seq_next should increase position index"
https://www.spinics.net/lists/linux-s390/msg30430.html

It was reviewed by Cornelia Huck
https://www.spinics.net/lists/linux-s390/msg30433.html

> On 24.01.20 06:48, Vasily Averin wrote:
>> 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/*
>>
>> Following patch fixes s390-related file
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=206283
>>
>> Vasily Averin (1):
>>   cio_ignore_proc_seq_next should increase position index
>>
>>  drivers/s390/cio/blacklist.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>