Re: [PATCH v2.1 3/5] media: Refactor copying IOCTL arguments from and to user space

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sakari,

Thank you for the patch.

On Wednesday 04 May 2016 16:09:51 Sakari Ailus wrote:
> Refactor copying the IOCTL argument structs from the user space and back,
> in order to reduce code copied around and make the implementation more
> robust.
> 
> As a result, the copying is done while not holding the graph mutex.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
> since v2:
> 
> - Remove function to calculate maximum argument size, replace by a char
>   array of 256 or kmalloc() if that's too small.
> 
>  drivers/media/media-device.c | 194 +++++++++++++++++++---------------------
>  1 file changed, 94 insertions(+), 100 deletions(-)
> 
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index 9b5a88d..0797e4b 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -59,27 +59,24 @@ static int media_device_close(struct file *filp)
>  }
> 
>  static int media_device_get_info(struct media_device *dev,
> -				 struct media_device_info __user *__info)
> +				 struct media_device_info *info)
>  {
> -	struct media_device_info info;
> -
> -	memset(&info, 0, sizeof(info));
> +	memset(info, 0, sizeof(*info));
> 
>  	if (dev->driver_name[0])
> -		strlcpy(info.driver, dev->driver_name, sizeof(info.driver));
> +		strlcpy(info->driver, dev->driver_name, sizeof(info->driver));
>  	else
> -		strlcpy(info.driver, dev->dev->driver->name, sizeof(info.driver));
> +		strlcpy(info->driver, dev->dev->driver->name,
> +			sizeof(info->driver));
> 
> -	strlcpy(info.model, dev->model, sizeof(info.model));
> -	strlcpy(info.serial, dev->serial, sizeof(info.serial));
> -	strlcpy(info.bus_info, dev->bus_info, sizeof(info.bus_info));
> +	strlcpy(info->model, dev->model, sizeof(info->model));
> +	strlcpy(info->serial, dev->serial, sizeof(info->serial));
> +	strlcpy(info->bus_info, dev->bus_info, sizeof(info->bus_info));
> 
> -	info.media_version = MEDIA_API_VERSION;
> -	info.hw_revision = dev->hw_revision;
> -	info.driver_version = dev->driver_version;
> +	info->media_version = MEDIA_API_VERSION;
> +	info->hw_revision = dev->hw_revision;
> +	info->driver_version = dev->driver_version;
> 
> -	if (copy_to_user(__info, &info, sizeof(*__info)))
> -		return -EFAULT;
>  	return 0;
>  }
> 
> @@ -101,29 +98,25 @@ static struct media_entity *find_entity(struct
> media_device *mdev, u32 id) }
> 
>  static long media_device_enum_entities(struct media_device *mdev,
> -				       struct media_entity_desc __user *uent)
> +				       struct media_entity_desc *entd)
>  {
>  	struct media_entity *ent;
> -	struct media_entity_desc u_ent;
> -
> -	memset(&u_ent, 0, sizeof(u_ent));
> -	if (copy_from_user(&u_ent.id, &uent->id, sizeof(u_ent.id)))
> -		return -EFAULT;
> -
> -	ent = find_entity(mdev, u_ent.id);
> 
> +	ent = find_entity(mdev, entd->id);
>  	if (ent == NULL)
>  		return -EINVAL;
> 
> -	u_ent.id = media_entity_id(ent);
> +	memset(entd, 0, sizeof(*entd));
> +
> +	entd->id = media_entity_id(ent);
>  	if (ent->name)
> -		strlcpy(u_ent.name, ent->name, sizeof(u_ent.name));
> -	u_ent.type = ent->function;
> -	u_ent.revision = 0;		/* Unused */
> -	u_ent.flags = ent->flags;
> -	u_ent.group_id = 0;		/* Unused */
> -	u_ent.pads = ent->num_pads;
> -	u_ent.links = ent->num_links - ent->num_backlinks;
> +		strlcpy(entd->name, ent->name, sizeof(entd->name));
> +	entd->type = ent->function;
> +	entd->revision = 0;		/* Unused */
> +	entd->flags = ent->flags;
> +	entd->group_id = 0;		/* Unused */
> +	entd->pads = ent->num_pads;
> +	entd->links = ent->num_links - ent->num_backlinks;
> 
>  	/*
>  	 * Workaround for a bug at media-ctl <= v1.10 that makes it to
> @@ -139,14 +132,13 @@ static long media_device_enum_entities(struct
> media_device *mdev, if (ent->function < MEDIA_ENT_F_OLD_BASE ||
>  	    ent->function > MEDIA_ENT_T_DEVNODE_UNKNOWN) {
>  		if (is_media_entity_v4l2_subdev(ent))
> -			u_ent.type = MEDIA_ENT_F_V4L2_SUBDEV_UNKNOWN;
> +			entd->type = MEDIA_ENT_F_V4L2_SUBDEV_UNKNOWN;
>  		else if (ent->function != MEDIA_ENT_F_IO_V4L)
> -			u_ent.type = MEDIA_ENT_T_DEVNODE_UNKNOWN;
> +			entd->type = MEDIA_ENT_T_DEVNODE_UNKNOWN;
>  	}
> 
> -	memcpy(&u_ent.raw, &ent->info, sizeof(ent->info));
> -	if (copy_to_user(uent, &u_ent, sizeof(u_ent)))
> -		return -EFAULT;
> +	memcpy(&entd->raw, &ent->info, sizeof(ent->info));
> +
>  	return 0;
>  }
> 
> @@ -158,8 +150,8 @@ static void media_device_kpad_to_upad(const struct
> media_pad *kpad, upad->flags = kpad->flags;
>  }
> 
> -static long __media_device_enum_links(struct media_device *mdev,
> -				      struct media_links_enum *links)
> +static long media_device_enum_links(struct media_device *mdev,
> +				    struct media_links_enum *links)
>  {
>  	struct media_entity *entity;
> 
> @@ -206,64 +198,35 @@ static long __media_device_enum_links(struct
> media_device *mdev, return 0;
>  }
> 
> -static long media_device_enum_links(struct media_device *mdev,
> -				    struct media_links_enum __user *ulinks)
> -{
> -	struct media_links_enum links;
> -	int rval;
> -
> -	if (copy_from_user(&links, ulinks, sizeof(links)))
> -		return -EFAULT;
> -
> -	rval = __media_device_enum_links(mdev, &links);
> -	if (rval < 0)
> -		return rval;
> -
> -	if (copy_to_user(ulinks, &links, sizeof(*ulinks)))
> -		return -EFAULT;
> -
> -	return 0;
> -}
> -
>  static long media_device_setup_link(struct media_device *mdev,
> -				    struct media_link_desc __user *_ulink)
> +				    struct media_link_desc *linkd)
>  {
>  	struct media_link *link = NULL;
> -	struct media_link_desc ulink;
>  	struct media_entity *source;
>  	struct media_entity *sink;
> -	int ret;
> -
> -	if (copy_from_user(&ulink, _ulink, sizeof(ulink)))
> -		return -EFAULT;
> 
>  	/* Find the source and sink entities and link.
>  	 */
> -	source = find_entity(mdev, ulink.source.entity);
> -	sink = find_entity(mdev, ulink.sink.entity);
> +	source = find_entity(mdev, linkd->source.entity);
> +	sink = find_entity(mdev, linkd->sink.entity);
> 
>  	if (source == NULL || sink == NULL)
>  		return -EINVAL;
> 
> -	if (ulink.source.index >= source->num_pads ||
> -	    ulink.sink.index >= sink->num_pads)
> +	if (linkd->source.index >= source->num_pads ||
> +	    linkd->sink.index >= sink->num_pads)
>  		return -EINVAL;
> 
> -	link = media_entity_find_link(&source->pads[ulink.source.index],
> -				      &sink->pads[ulink.sink.index]);
> +	link = media_entity_find_link(&source->pads[linkd->source.index],
> +				      &sink->pads[linkd->sink.index]);
>  	if (link == NULL)
>  		return -EINVAL;
> 
>  	/* Setup the link on both entities. */
> -	ret = __media_entity_setup_link(link, ulink.flags);
> -
> -	if (copy_to_user(_ulink, &ulink, sizeof(ulink)))
> -		return -EFAULT;
> -
> -	return ret;
> +	return __media_entity_setup_link(link, linkd->flags);
>  }
> 
> -static long __media_device_get_topology(struct media_device *mdev,
> +static long media_device_get_topology(struct media_device *mdev,
>  				      struct media_v2_topology *topo)
>  {
>  	struct media_entity *entity;
> @@ -400,35 +363,50 @@ static long __media_device_get_topology(struct
> media_device *mdev, return ret;
>  }
> 
> -static long media_device_get_topology(struct media_device *mdev,
> -				      struct media_v2_topology __user *utopo)
> +static long copy_arg_from_user(void *karg, void __user *uarg, unsigned int
> cmd) {
> -	struct media_v2_topology ktopo;
> -	int ret;
> -
> -	if (copy_from_user(&ktopo, utopo, sizeof(ktopo)))
> +	/* All media IOCTLs are _IOWR() */
> +	if (copy_from_user(karg, uarg, _IOC_SIZE(cmd)))
>  		return -EFAULT;
> 
> -	ret = __media_device_get_topology(mdev, &ktopo);
> -	if (ret < 0)
> -		return ret;
> +	return 0;
> +}
> 
> -	if (copy_to_user(utopo, &ktopo, sizeof(*utopo)))
> +static long copy_arg_to_user(void __user *uarg, void *karg, unsigned int
> cmd) +{
> +	/* All media IOCTLs are _IOWR() */
> +	if (copy_to_user(uarg, karg, _IOC_SIZE(cmd)))
>  		return -EFAULT;
> 
>  	return 0;
>  }
> 
> -#define MEDIA_IOC(__cmd, func)						\
> -	[_IOC_NR(MEDIA_IOC_##__cmd)] = {				\
> -		.cmd = MEDIA_IOC_##__cmd,				\
> -		.fn = (long (*)(struct media_device *, void __user *))func,    \
> +#ifdef CONFIG_COMPAT
> +/* Only compat IOCTLs need this right now. */
> +static long copy_arg_to_user_nop(void __user *uarg, void *karg,
> +				 unsigned int cmd)
> +{
> +	return 0;
> +}
> +#endif
> +
> +#define MEDIA_IOC_ARG(__cmd, func, from_user, to_user)	\
> +	[_IOC_NR(MEDIA_IOC_##__cmd)] = {		\
> +		.cmd = MEDIA_IOC_##__cmd,		\
> +		.fn = (long (*)(struct media_device *, void *))func,	\
> +		.arg_from_user = from_user,		\
> +		.arg_to_user = to_user,			\
>  	}
> 
> +#define MEDIA_IOC(__cmd, func)						\
> +	MEDIA_IOC_ARG(__cmd, func, copy_arg_from_user, copy_arg_to_user)
> +
>  /* the table is indexed by _IOC_NR(cmd) */
>  struct media_ioctl_info {
>  	unsigned int cmd;
> -	long (*fn)(struct media_device *dev, void __user *arg);
> +	long (*fn)(struct media_device *dev, void *arg);
> +	long (*arg_from_user)(void *karg, void __user *uarg, unsigned int cmd);
> +	long (*arg_to_user)(void __user *uarg, void *karg, unsigned int cmd);
>  };
> 
>  static inline long is_valid_ioctl(const struct media_ioctl_info *info,
> @@ -445,6 +423,7 @@ static long __media_device_ioctl(
>  	struct media_devnode *devnode = media_devnode_data(filp);
>  	struct media_device *dev = to_media_device(devnode);
>  	const struct media_ioctl_info *info;
> +	char __karg[256], *karg = __karg;
>  	long ret;
> 
>  	ret = is_valid_ioctl(info_array, info_array_len, cmd);
> @@ -453,10 +432,24 @@ static long __media_device_ioctl(
> 
>  	info = &info_array[_IOC_NR(cmd)];
> 
> +	if (_IOC_SIZE(info->cmd) > sizeof(__karg)) {
> +		karg = kmalloc(_IOC_SIZE(info->cmd), GFP_KERNEL);
> +		if (!karg)
> +			return -ENOMEM;
> +	}
> +
> +	info->arg_from_user(karg, arg, cmd);
> +
>  	mutex_lock(&dev->graph_mutex);
> -	ret = info->fn(dev, arg);
> +	ret = info->fn(dev, karg);
>  	mutex_unlock(&dev->graph_mutex);
> 
> +	if (!ret)

How about if (!ret && info->arg_to_user) instead, and getting rid of 
copy_arg_to_user_nop() ?

Apart from that,

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> +		ret = info->arg_to_user(arg, karg, cmd);
> +
> +	if (karg != __karg)
> +		kfree(karg);
> +
>  	return ret;
>  }
> 
> @@ -485,23 +478,24 @@ struct media_links_enum32 {
>  	__u32 reserved[4];
>  };
> 
> -static long media_device_enum_links32(struct media_device *mdev,
> -				      struct media_links_enum32 __user *ulinks)
> +static long from_user_enum_links32(void *karg, void __user *uarg,
> +				   unsigned int cmd)
>  {
> -	struct media_links_enum links;
> +	struct media_links_enum *links = karg;
> +	struct media_links_enum32 __user *ulinks = uarg;
>  	compat_uptr_t pads_ptr, links_ptr;
> 
> -	memset(&links, 0, sizeof(links));
> +	memset(links, 0, sizeof(*links));
> 
> -	if (get_user(links.entity, &ulinks->entity)
> +	if (get_user(links->entity, &ulinks->entity)
>  	    || get_user(pads_ptr, &ulinks->pads)
>  	    || get_user(links_ptr, &ulinks->links))
>  		return -EFAULT;
> 
> -	links.pads = compat_ptr(pads_ptr);
> -	links.links = compat_ptr(links_ptr);
> +	links->pads = compat_ptr(pads_ptr);
> +	links->links = compat_ptr(links_ptr);
> 
> -	return __media_device_enum_links(mdev, &links);
> +	return 0;
>  }
> 
>  #define MEDIA_IOC_ENUM_LINKS32		_IOWR('|', 0x02, struct 
media_links_enum32)
> @@ -509,7 +503,7 @@ static long media_device_enum_links32(struct
> media_device *mdev, static const struct media_ioctl_info
> compat_ioctl_info[] = {
>  	MEDIA_IOC(DEVICE_INFO, media_device_get_info),
>  	MEDIA_IOC(ENUM_ENTITIES, media_device_enum_entities),
> -	MEDIA_IOC(ENUM_LINKS32, media_device_enum_links32),
> +	MEDIA_IOC_ARG(ENUM_LINKS32, media_device_enum_links,
> from_user_enum_links32, copy_arg_to_user_nop), MEDIA_IOC(SETUP_LINK,
> media_device_setup_link),
>  	MEDIA_IOC(G_TOPOLOGY, media_device_get_topology),
>  };

-- 
Regards,

Laurent Pinchart