• Vasily Averin's avatar
    fs/seq_file.c: seq_read(): add info message about buggy .next functions · 3bfa7e14
    Vasily Averin authored
    Patch series "seq_file .next functions should increase position index".
    
    In Aug 2018 NeilBrown noticed commit 1f4aace6 ("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=206283Signed-off-by: default avatarVasily Averin <vvs@virtuozzo.com>
    Signed-off-by: default avatarAndrew 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.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    3bfa7e14