linux-kernel - Re: [PATCH] nilfs2: fix memory leak in nilfs_sysfs_create_device

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Message-ID: <CAD-N9QVa08v6BU2XF6hohUBpjqgZys80UPf8ywLzUCv7WnkpcQ@mail.gmail.com>
Date:   Mon, 13 Sep 2021 13:23:59 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     Ryusuke Konishi <konishi.ryusuke@...il.com>,
        linux-nilfs@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nilfs2: fix memory leak in nilfs_sysfs_create_device_group

There are many commits related to memory leak fix in nilfs_sysfs.

4 days nilfs2: fix memory leak in nilfs_sysfs_delete_snapshot_group
4 days nilfs2: fix memory leak in nilfs_sysfs_create_snapshot_group
4 days nilfs2: fix memory leak in nilfs_sysfs_delete_##name##_group
4 days nilfs2: fix memory leak in nilfs_sysfs_create_##name##_group
4 days nilfs2: fix NULL pointer in nilfs_##name##_attr_release
4 days nilfs2: fix memory leak in nilfs_sysfs_create_device_group

This thread can be closed.

Best regards,
Dongliang Mu

On Tue, Sep 7, 2021 at 12:00 PM Dongliang Mu <mudongliangabcd@...il.com> wrote:
>
> On Tue, Sep 7, 2021 at 12:47 AM Pavel Skripkin <paskripkin@...il.com> wrote:
> >
> > On 9/6/21 18:56, Pavel Skripkin wrote:
> > > On 9/6/21 08:43, Dongliang Mu wrote:
> > >> On Mon, Sep 6, 2021 at 12:13 PM Dongliang Mu <mudongliangabcd@...il.com> wrote:
> > >>>
> > >>> The commit 8fd0c1b0647a ("nilfs2: fix memory leak in
> > >>> nilfs_sysfs_delete_device_group") adds a kobject_put to free the leaking
> > >>> object name. However, it is incomplete to only add kobject_put in the
> > >>> nilfs_sysfs_delete_device_group. The function
> > >>> nilfs_sysfs_create_device_group also needs the kobject_put to
> > >>> free the object name in the error handling part.
> > >>>
> > >>> Fix this by adding kobject_put in the error handling code of
> > >>> nilfs_sysfs_create_device_group.
> > >>
> > >> Even after I add this patch, my local syzkaller still reports this
> > >> memory leak one hour later. Therefore, there are some other paths or
> > >> magics which can trigger the memory leak. I need to dig deeper.
> > >>
> > >> Pavel, do you have any idea about this crash report?
> > >>
> > >> BUG: memory leak
> > >> unreferenced object 0xffff88804a1a8a60 (size 32):
> > >>    comm "syz-executor", pid 14551, jiffies 4294960586 (age 14.780s)
> > >>    hex dump (first 32 bytes):
> > >>      6c 6f 6f 70 35 00 00 00 00 00 00 00 00 00 00 00  loop5...........
> > >>      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> > >>    backtrace:
> > >>      [<ffffffff814750c6>] kstrdup+0x36/0x70
> > >>      [<ffffffff81475153>] kstrdup_const+0x53/0x80
> > >>      [<ffffffff822773a2>] kvasprintf_const+0xc2/0x110
> > >>      [<ffffffff82337c5b>] kobject_set_name_vargs+0x3b/0xe0
> > >>      [<ffffffff823385ed>] kobject_init_and_add+0x6d/0xc0
> > >>      [<ffffffff81d2bd08>] nilfs_sysfs_create_device_group+0x98/0x3a0
> > >>      [<ffffffff81d14fc4>] init_nilfs+0x424/0x580
> > >>      [<ffffffff81d02962>] nilfs_mount+0x532/0x8c0
> > >>      [<ffffffff815c754b>] legacy_get_tree+0x2b/0x90
> > >>      [<ffffffff81565158>] vfs_get_tree+0x28/0x100
> > >>      [<ffffffff815a3a82>] path_mount+0xb92/0xfe0
> > >>      [<ffffffff815a3f71>] do_mount+0xa1/0xc0
> > >>      [<ffffffff815a4584>] __x64_sys_mount+0xf4/0x160
> > >>      [<ffffffff8433fd35>] do_syscall_64+0x35/0xb0
> > >>      [<ffffffff84400068>] entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >>
> > >>
> > >
> > > Hi, Dongliang!
> > >
> > >
> > > This report says nothing to me... It shows, that there is missing
> > > kobject_put() somewhere. I think, we need a reproducer for this leak,
> > > otherwise only code review can help :(
> > >
> > >
> > >
> >
> > Hm, I guess, I see... We should call kobject_put() in case of
> > kobject_init_and_add() failure:
> >
> > lib/kobject.c:459
> >
> >   * If this function returns an error, kobject_put() must be called to
> >   * properly clean up the memory associated with the object.  This is the
> >
> >
> > so I suggest:
> >
> > diff --git a/fs/nilfs2/sysfs.c b/fs/nilfs2/sysfs.c
> > index 68e8d61e28dd..e8717f4ba2a1 100644
> > --- a/fs/nilfs2/sysfs.c
> > +++ b/fs/nilfs2/sysfs.c
> > @@ -1026,6 +1026,7 @@ int nilfs_sysfs_create_device_group(struct
> > super_block *sb)        kobject_del(&nilfs->ns_dev_kobj);
> >
> >   free_dev_subgroups:
> > +       kobject_put(&nilfs->ns_dev_kobj);
> >         kfree(nilfs->ns_dev_subgroups);
> >
> >   failed_create_device_group:
> >
> >
> > This patch should fix 2 memory leaks :)
>
> Yes. We should move kobject_put from the label cleanup_dev_kobject to
> free_dev_subgroups.
>
> However, I tried the syz reproducer just sent to you. The memory leak
> is still there.
>
> >
> >
> >
> >
> > With regards,
> > Pavel Skripkin