netdev - [PATCH 0/6] netdev: seq_file .next functions should increase position index

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Date:   Thu, 23 Jan 2020 10:11:01 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     Vishal Kulkarni <vishal@...lsio.com>, netdev@...r.kernel.org
Subject: [PATCH 0/6] netdev: 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/*

This patch-set fixes files related to netdev@ 

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

Vasily Averin (6):
  seq_tab_next() should increase position index
  l2t_seq_next should increase position index
  vcc_seq_next should increase position index
  neigh_stat_seq_next() should increase position index
  rt_cpu_seq_next should increase position index
  ipv6_route_seq_next should increase position index

 drivers/net/ethernet/chelsio/cxgb4/cxgb4_debugfs.c | 3 +--
 drivers/net/ethernet/chelsio/cxgb4/l2t.c           | 3 +--
 net/atm/proc.c                                     | 3 +--
 net/core/neighbour.c                               | 1 +
 net/ipv4/route.c                                   | 1 +
 net/ipv6/ip6_fib.c                                 | 7 ++-----
 6 files changed, 7 insertions(+), 11 deletions(-)

-- 
1.8.3.1