linux-kernel - Re: [PATCH] proc: add proc_seq

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Date:   Tue, 26 Jun 2018 08:20:52 -0400 (EDT)
From:   Chunyu Hu <chuhu@...hat.com>
To:     linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
        Christoph Hellwig <hch@....de>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] proc: add proc_seq_release



----- Original Message -----
> From: "Christoph Hellwig" <hch@....de>
> To: "Chunyu Hu" <chuhu@...hat.com>
> Cc: viro@...iv.linux.org.uk, hch@....de, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
> Sent: Monday, June 11, 2018 2:23:54 PM
> Subject: Re: [PATCH] proc: add proc_seq_release
> 
> On Sun, Jun 10, 2018 at 03:51:24AM +0800, Chunyu Hu wrote:
> > kmemleak reported some memory leak on reading proc files. After adding
> > some debug lines, find that proc_seq_fops is using seq_release as
> > release handler, which won't handle the free of 'private' field of
> > seq_file, while in fact the open handler proc_seq_open could create
> > the private data with __seq_open_private when state_size is greater
> > than zero. So after reading files created with proc_create_seq_private,
> > such as /proc/timer_list and /proc/vmallocinfo, the private mem of a
> > seq_file is not freed. Fix it by adding the paired proc_seq_release
> > as the default release handler of proc_seq_ops instead of seq_release.
> 
> Indeed, thanks for the patch.
> 
> Reviewed-by: Christoph Hellwig <hch@....de>
> 

What's our plan for this issue? We can still see the leaking in 4.18-RC2. 

1) Run 'cat /proc/timer_list' then
2) echo scan > /sys/kernel/debug/kmemleak
3) cat /sys/kernel/debug/kmemleak

each time, it leaks 16 bytes.

unreferenced object 0xffff880017525120 (size 16):
  comm "cat", pid 4682, jiffies 4294964743 (age 46.880s)
  hex dump (first 16 bytes):
    04 00 00 00 01 00 00 00 42 00 96 e7 3f 00 00 00  ........B...?...
  backtrace:
    [<000000006f6b5d90>] seq_open_private+0x25/0x40
    [<00000000d94d91aa>] proc_seq_open+0xca/0x120
    [<00000000d5609077>] proc_reg_open+0x1d4/0x5b0
    [<0000000036a3d49c>] do_dentry_open+0x7d6/0x1010
    [<00000000d4fb0a82>] vfs_open+0x170/0x2b0
    [<00000000f3bf21b4>] path_openat+0x760/0x3750
    [<00000000b0d4e66c>] do_filp_open+0x1bb/0x2c0
    [<0000000063b53236>] do_sys_open+0x2b2/0x490
    [<00000000a5249c62>] do_syscall_64+0xd3/0x6e0
    [<000000006f9f8436>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
    [<000000001d702cb2>] 0xffffffffffffffff


-- 
Regards,
Chunyu Hu