Re: [PATCH] nilfs2: fix memory leak in nilfs_sysfs_create_device_group

[Dongliang Mu]

On Mon, Sep 6, 2021 at 11:56 PM Pavel Skripkin <paskripkin@xxxxxxxxx> wrote:
>
> On 9/6/21 08:43, Dongliang Mu wrote:
> > On Mon, Sep 6, 2021 at 12:13 PM Dongliang Mu <mudongliangabcd@xxxxxxxxx> 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 :(

I have attached a syz reproducer to this email. Even if the kernel is
patched with your patch and my patch, it still triggers a memory leak.

>
>
>
> With regards,
> Pavel Skripkin

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