Re: [PATCH] nilfs2: fix memory leak in nilfs_sysfs_create_device_group
From: Dongliang Mu
Date: Tue Sep 07 2021 - 00:00:42 EST
On Tue, Sep 7, 2021 at 12:47 AM Pavel Skripkin <paskripkin@xxxxxxxxx> 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@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 :(
> Hm, I guess, I see... We should call kobject_put() in case of
> kobject_init_and_add() failure:
> * 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);
> + kobject_put(&nilfs->ns_dev_kobj);
> This patch should fix 2 memory leaks :)
Yes. We should move kobject_put from the label cleanup_dev_kobject to
However, I tried the syz reproducer just sent to you. The memory leak
is still there.
> With regards,
> Pavel Skripkin