Re: [PATCH] vfio/mdev: fix possible memory leak in module init funcs

[Ruan Jinjie]

On 2022/12/1 7:06, Alex Williamson wrote:
> [Cc +vfio-ap, vfio-ccw]
> 
> On Fri, 18 Nov 2022 11:28:27 +0800
> ruanjinjie <ruanjinjie@xxxxxxxxxx> 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@xxxxxxxxxx>
>> ---
>>  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:
I think the reason is vfio-ap driver error path has common unwind to do
before device_register, otherwise it can return just after put_device or
device_unregister.
> 
> 	...
>         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.
The patch do not change the original error path, just add missing
put_device out of the normal error path if device_register fails , so
there is no risk of calling both device_unregister() and put_device().
> 
> 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,
>