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

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Date:   Mon, 6 Sep 2021 13:43:26 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Ryusuke Konishi <konishi.ryusuke@...il.com>
Cc:     Pavel Skripkin <paskripkin@...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

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


>
> Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
> ---
>  fs/nilfs2/sysfs.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/fs/nilfs2/sysfs.c b/fs/nilfs2/sysfs.c
> index 68e8d61e28dd..7ab60711ca76 100644
> --- a/fs/nilfs2/sysfs.c
> +++ b/fs/nilfs2/sysfs.c
> @@ -1024,6 +1024,7 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
>
>  cleanup_dev_kobject:
>         kobject_del(&nilfs->ns_dev_kobj);
> +       kobject_put(&nilfs->ns_dev_kobj);
>
>  free_dev_subgroups:
>         kfree(nilfs->ns_dev_subgroups);
> --
> 2.25.1
>