Re: [PATCH] drm/vkms: Fix use after free and double free on init error

[Louis Chauvet <louis.chauvet@bootlin.com>]

Le 14/02/2025 à 16:44, José Expósito a écrit :
> On Thu, Feb 13, 2025 at 04:11:20PM +0100, Louis Chauvet wrote:
>> On 12/02/25 - 15:06, Louis Chauvet wrote:
>>>
>>>
>>> Le 12/02/2025 à 09:53, Thomas Zimmermann a écrit :
>>>>
>>>>
>>>> Am 12.02.25 um 09:49 schrieb José Expósito:
>>>>> If the driver initialization fails, the vkms_exit() function might
>>>>> access an uninitialized or freed default_config pointer and it might
>>>>> double free it.
>>>>>
>>>>> Fix both possible errors by initializing default_config only when the
>>>>> driver initialization succeeded.
>>>>>
>>>>> Reported-by: Louis Chauvet <louis.chauvet@bootlin.com>
>>>>> Link: https://lore.kernel.org/all/Z5uDHcCmAwiTsGte@louis-chauvet-laptop/
>>>>> Fixes: 2df7af93fdad ("drm/vkms: Add vkms_config type")
>>>>> Signed-off-by: José Expósito <jose.exposito89@gmail.com>
>>>>
>>>> Reviewed-by: Thomas Zimmermann <tzimmremann@suse.de>
>>>
>>> Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
>>>
>>> lore.kernel.org is broken currently, to avoid doing mistakes, I will wait
>>> for it to be working again so I can apply your patch using dim+b4.
>>>
>>> (I removed danvet.vetter@ffwl.ch from CC, the mail server rejected the mail)
>>>
>>> Thanks!
>>> Louis Chauvet
>>
>> Hello,
>>
>> I tried to apply the commit, but I have a strange issue:
>>
>> 	$ dim push
>> 	Enumerating objects: 13, done.
>> 	Counting objects: 100% (13/13), done.
>> 	Delta compression using up to 20 threads
>> 	Compressing objects: 100% (7/7), done.
>> 	Writing objects: 100% (7/7), 1.67 KiB | 113.00 KiB/s, done.
>> 	Total 7 (delta 6), reused 0 (delta 0), pack-reused 0 (from 0)
>> 	remote:
>> 	remote: ========================================================================
>> 	remote:
>> 	remote:    Equinix is shutting down its operations with us on April 30, 2025.
>> 	remote:    They have graciously supported us for almost 5 years, but all good
>> 	remote:    things come to an end. Given the time frame, it's going to be hard
>> 	remote:       to make a smooth transition of the cluster to somewhere else
>> 	remote: ([TBD](https://gitlab.freedesktop.org/freedesktop/freedesktop/-/issues/2011)).
>> 	remote:     Please expect in the next months some hiccups in the service and
>> 	remote:    probably at least a full week of downtime to transfer gitlab to a
>> 	remote:                different place. All help is appreciated.
>> 	remote:
>> 	remote: ========================================================================
>> 	remote:
>> 	To gitlab.freedesktop.org:drm/misc/kernel.git
>> 	   ff3881cc6a58..ed15511a773d  drm-misc-next -> drm-misc-next
>> 	Pushing drm-misc-fixes to for-linux-next-fixes... Everything up-to-date
>> 	Done.
>> 	Out of merge window. Pushing drm-misc-next to for-linux-next...
>> 	remote:
>> 	remote: ========================================================================
>> 	remote:
>> 	remote: ERROR: Internal API unreachable
>> 	
>> 	remote:
>> 	remote: ========================================================================
>> 	remote:
>> 	fatal: Could not read from remote repository.
>> 	
>> 	Please make sure you have the correct access rights
>> 	and the repository exists.
>>
>> Is this expected?
> 
> I guess you managed to fix the issue. I git pull-ed this morning and
> the patch was applied.

It is applied to drm-misc/drm-misc-next, but not on drm-misc/for-linux-next.

I don't know if this is important and how to fix the issue if yes.

Louis Chauvet

> Jose
>   
>> Thanks,
>> Louis Chauvet
>>
>>>> Thanks for posting this patch separately.
>>>>
>>>> Best regards
>>>> Thomas
>>>>
>>>>> ---
>>>>>     drivers/gpu/drm/vkms/vkms_drv.c | 15 +++++++++------
>>>>>     1 file changed, 9 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
>>>>> index 7c142bfc3bd9..b6de91134a22 100644
>>>>> --- a/drivers/gpu/drm/vkms/vkms_drv.c
>>>>> +++ b/drivers/gpu/drm/vkms/vkms_drv.c
>>>>> @@ -235,17 +235,19 @@ static int __init vkms_init(void)
>>>>>     	if (!config)
>>>>>     		return -ENOMEM;
>>>>> -	default_config = config;
>>>>> -
>>>>>     	config->cursor = enable_cursor;
>>>>>     	config->writeback = enable_writeback;
>>>>>     	config->overlay = enable_overlay;
>>>>>     	ret = vkms_create(config);
>>>>> -	if (ret)
>>>>> +	if (ret) {
>>>>>     		kfree(config);
>>>>> +		return ret;
>>>>> +	}
>>>>> -	return ret;
>>>>> +	default_config = config;
>>>>> +
>>>>> +	return 0;
>>>>>     }
>>>>>     static void vkms_destroy(struct vkms_config *config)
>>>>> @@ -269,9 +271,10 @@ static void vkms_destroy(struct vkms_config *config)
>>>>>     static void __exit vkms_exit(void)
>>>>>     {
>>>>> -	if (default_config->dev)
>>>>> -		vkms_destroy(default_config);
>>>>> +	if (!default_config)
>>>>> +		return;
>>>>> +	vkms_destroy(default_config);
>>>>>     	kfree(default_config);
>>>>>     }
>>>>
>>>
>>> -- 
>>> Louis Chauvet, Bootlin
>>> Embedded Linux and Kernel engineering
>>> https://bootlin.com
>>>

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com