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Date:   Wed, 30 Nov 2022 16:06:22 -0700
From:   Alex Williamson <alex.williamson@redhat.com>
To:     ruanjinjie <ruanjinjie@huawei.com>
Cc:     <kwankhede@nvidia.com>, <kraxel@redhat.com>, <cjia@nvidia.com>,
        <kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        akrowiak@linux.ibm.com, pasic@linux.ibm.com, jjherne@linux.ibm.com,
        farman@linux.ibm.com, mjrosato@linux.ibm.com
Subject: Re: [PATCH] vfio/mdev: fix possible memory leak in module init
 funcs
Message-ID: <20221130160622.0cf3e47d.alex.williamson@redhat.com>
In-Reply-To: <20221118032827.3725190-1-ruanjinjie@huawei.com>
References: <20221118032827.3725190-1-ruanjinjie@huawei.com>
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[Cc +vfio-ap, vfio-ccw]

On Fri, 18 Nov 2022 11:28:27 +0800
ruanjinjie <ruanjinjie@huawei.com> wrote:

> Inject fault while probing module, if device_register() fails,
> but the refcount of kobject is not decreased to 0, the name
> allocated in dev_set_name() is leaked. Fix this by calling
> put_device(), so that name can be freed in callback function
> kobject_cleanup().
> 
> unreferenced object 0xffff88807d687008 (size 8):
>   comm "modprobe", pid 8280, jiffies 4294807686 (age 12.378s)
>   hex dump (first 8 bytes):
>     6d 64 70 79 00 6b 6b a5                          mdpy.kk.
>   backtrace:
>     [<ffffffff8174f19e>] __kmalloc_node_track_caller+0x4e/0x150
>     [<ffffffff81731d53>] kstrdup+0x33/0x60
>     [<ffffffff83aa1421>] kobject_set_name_vargs+0x41/0x110
>     [<ffffffff82d91abb>] dev_set_name+0xab/0xe0
>     [<ffffffffa0260105>] 0xffffffffa0260105
>     [<ffffffff81001c27>] do_one_initcall+0x87/0x2e0
>     [<ffffffff813739cb>] do_init_module+0x1ab/0x640
>     [<ffffffff81379d20>] load_module+0x5d00/0x77f0
>     [<ffffffff8137bc40>] __do_sys_finit_module+0x110/0x1b0
>     [<ffffffff83c944a5>] do_syscall_64+0x35/0x80
>     [<ffffffff83e0006a>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> unreferenced object 0xffff888101ccbcf8 (size 8):
>   comm "modprobe", pid 15662, jiffies 4295164481 (age 13.282s)
>   hex dump (first 8 bytes):
>     6d 74 74 79 00 6b 6b a5                          mtty.kk.
>   backtrace:
>     [<ffffffff8174f19e>] __kmalloc_node_track_caller+0x4e/0x150
>     [<ffffffff81731d53>] kstrdup+0x33/0x60
>     [<ffffffff83aa1421>] kobject_set_name_vargs+0x41/0x110
>     [<ffffffff82d91abb>] dev_set_name+0xab/0xe0
>     [<ffffffffa0248134>] 0xffffffffa0248134
>     [<ffffffff81001c27>] do_one_initcall+0x87/0x2e0
>     [<ffffffff813739cb>] do_init_module+0x1ab/0x640
>     [<ffffffff81379d20>] load_module+0x5d00/0x77f0
>     [<ffffffff8137bc40>] __do_sys_finit_module+0x110/0x1b0
>     [<ffffffff83c944a5>] do_syscall_64+0x35/0x80
>     [<ffffffff83e0006a>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> unreferenced object 0xffff88810177c6c8 (size 8):
>   comm "modprobe", pid 23657, jiffies 4295314656 (age 13.227s)
>   hex dump (first 8 bytes):
>     6d 62 6f 63 68 73 00 a5                          mbochs..
>   backtrace:
>     [<ffffffff8174f19e>] __kmalloc_node_track_caller+0x4e/0x150
>     [<ffffffff81731d53>] kstrdup+0x33/0x60
>     [<ffffffff83aa1421>] kobject_set_name_vargs+0x41/0x110
>     [<ffffffff82d91abb>] dev_set_name+0xab/0xe0
>     [<ffffffffa0248124>] 0xffffffffa0248124
>     [<ffffffff81001c27>] do_one_initcall+0x87/0x2e0
>     [<ffffffff813739cb>] do_init_module+0x1ab/0x640
>     [<ffffffff81379d20>] load_module+0x5d00/0x77f0
>     [<ffffffff8137bc40>] __do_sys_finit_module+0x110/0x1b0
>     [<ffffffff83c944a5>] do_syscall_64+0x35/0x80
>     [<ffffffff83e0006a>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> Fixes: d61fc96f47fd ("sample: vfio mdev display - host device")
> Fixes: 9d1a546c53b4 ("docs: Sample driver to demonstrate how to use Mediated device framework.")
> Fixes: a5e6e6505f38 ("sample: vfio bochs vbe display (host device for bochs-drm)")
> Signed-off-by: ruanjinjie <ruanjinjie@huawei.com>
> ---
>  samples/vfio-mdev/mbochs.c | 4 +++-
>  samples/vfio-mdev/mdpy.c   | 4 +++-
>  samples/vfio-mdev/mtty.c   | 4 +++-
>  3 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
> index 117a8d799f71..1c47672be815 100644
> --- a/samples/vfio-mdev/mbochs.c
> +++ b/samples/vfio-mdev/mbochs.c
> @@ -1430,8 +1430,10 @@ static int __init mbochs_dev_init(void)
>  	dev_set_name(&mbochs_dev, "%s", MBOCHS_NAME);
>  
>  	ret = device_register(&mbochs_dev);
> -	if (ret)
> +	if (ret) {
> +		put_device(&mbochs_dev);
>  		goto err_class;
> +	}
>  
>  	ret = mdev_register_parent(&mbochs_parent, &mbochs_dev, &mbochs_driver,
>  				   mbochs_mdev_types,


vfio-ap has a similar unwind as the sample drivers, but actually makes
an attempt to catch this ex:

	...
        ret = device_register(&matrix_dev->device);
        if (ret)
                goto matrix_reg_err;

        ret = driver_register(&matrix_driver);
        if (ret)
                goto matrix_drv_err;

        return 0;

matrix_drv_err:
        device_unregister(&matrix_dev->device);
matrix_reg_err:
        put_device(&matrix_dev->device);
	...

So of the vfio drivers calling device_register(), vfio-ap is the only
one that does a put_device() if device_register() fails, but it also
seems sketchy to call both device_unregister() and put_device() in the
case that we exit via matrix_drv_err.

I wonder if all of these shouldn't adopt a flow like:

	ret = device_register(&dev);
	if (ret)
		goto err1;

	....

	return 0;

err2:
	device_del(&dev);
err1:
	put_device(&dev);

Thanks,

Alex

> diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c
> index 946e8cfde6fd..bfb93eaf535b 100644
> --- a/samples/vfio-mdev/mdpy.c
> +++ b/samples/vfio-mdev/mdpy.c
> @@ -717,8 +717,10 @@ static int __init mdpy_dev_init(void)
>  	dev_set_name(&mdpy_dev, "%s", MDPY_NAME);
>  
>  	ret = device_register(&mdpy_dev);
> -	if (ret)
> +	if (ret) {
> +		put_device(&mdpy_dev);
>  		goto err_class;
> +	}
>  
>  	ret = mdev_register_parent(&mdpy_parent, &mdpy_dev, &mdpy_driver,
>  				   mdpy_mdev_types,
> diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
> index e72085fc1376..dddb0619846c 100644
> --- a/samples/vfio-mdev/mtty.c
> +++ b/samples/vfio-mdev/mtty.c
> @@ -1330,8 +1330,10 @@ static int __init mtty_dev_init(void)
>  	dev_set_name(&mtty_dev.dev, "%s", MTTY_NAME);
>  
>  	ret = device_register(&mtty_dev.dev);
> -	if (ret)
> +	if (ret) {
> +		put_device(&mtty_dev.dev);
>  		goto err_class;
> +	}
>  
>  	ret = mdev_register_parent(&mtty_dev.parent, &mtty_dev.dev,
>  				   &mtty_driver, mtty_mdev_types,