linux-kernel - Re: [PATCH 03/13] drm/vkms: Extract vkms

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Message-ID: <Z6so3Xpd-z5zQJEK@fedora>
Date: Tue, 11 Feb 2025 11:39:25 +0100
From: José Expósito <jose.exposito89@...il.com>
To: Louis Chauvet <louis.chauvet@...tlin.com>
Cc: hamohammed.sa@...il.com, simona@...ll.ch, melissa.srw@...il.com,
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
	tzimmermann@...e.de, airlied@...il.com,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/13] drm/vkms: Extract vkms_config header

On Thu, Jan 30, 2025 at 02:48:13PM +0100, Louis Chauvet wrote:
> On 29/01/25 - 12:00, José Expósito wrote:
> > Creating a new vkms_config structure will be more complex once we
> > start adding more options.
> > 
> > Extract the vkms_config structure to its own header and source files
> > and add functions to create and delete a vkms_config and to initialize
> > debugfs.
> > 
> > Refactor, no functional changes.
> > 
> > Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> > Signed-off-by: José Expósito <jose.exposito89@...il.com>
> 
> Co-developped-by: Louis Chauvet <louis.chauvet@...tlin.com>
> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> Signed-off-by: José Expósito <jose.exposito89@...il.com>
> 
> [...]
> 
> > diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> > @@ -208,8 +189,7 @@ static int vkms_create(struct vkms_config *config)
> >  	if (ret)
> >  		goto out_devres;
> >  
> > -	drm_debugfs_add_files(&vkms_device->drm, vkms_config_debugfs_list,
> > -			      ARRAY_SIZE(vkms_config_debugfs_list));
> > +	vkms_config_register_debugfs(vkms_device);
> >  
> >  	ret = drm_dev_register(&vkms_device->drm, 0);
> >  	if (ret)
> > @@ -231,9 +211,9 @@ static int __init vkms_init(void)
> >  	int ret;
> >  	struct vkms_config *config;
> >  
> > -	config = kmalloc(sizeof(*config), GFP_KERNEL);
> > -	if (!config)
> > -		return -ENOMEM;
> > +	config = vkms_config_create();
> > +	if (IS_ERR(config))
> > +		return PTR_ERR(config);
> >  
> >  	default_config = config;
> >  
> > @@ -243,7 +223,7 @@ static int __init vkms_init(void)
> >  
> >  	ret = vkms_create(config);
> >  	if (ret)
> > -		kfree(config);
> > +		vkms_config_destroy(config);
> 
> I just have a question here: is it not a problem to kfree config (and 
> default_config) here? There is not risk to have a 
> use-after-free/double-free in vkms_exit?
> 
> >	return ret;
> >  }
> > @@ -272,7 +252,7 @@ static void __exit vkms_exit(void)
> >	if (default_config->dev)
> 
> The use-after-free may be here?
> 
> >		vkms_destroy(default_config);
> >  
> > -	kfree(default_config);
> > +	vkms_config_destroy(default_config);
> 
> And maybe double-free?
> 
> >  }
> 
> If this is not an issue (ie we have a garantee that vkms_exit is never
> called if vkms_init fails), you can add my

Good catch! This is a potential use after free/double free or, even worst,
on "if (default_config->dev)" default_config could be NULL.

Even though the bug is unrelated to this series (it was already there) I'll
include a fix in v2.
It'll be the first patch of the series and it could be merged independently.

Thanks,
Jose

> 
> Reviewed-by: Louis Chauvet <louis.chauvet@...tlin.com>
> 
> [...]