Re: [PATCH v4 5/5] media: Support variable size IOCTL arguments

Hans Verkuil
2016-08-22T12:55:09Z

On 08/11/2016 10:29 PM, Sakari Ailus wrote:
> Maintain a list of supported IOCTL argument sizes and allow only those in
> the list.
>
> As an additional bonus, IOCTL handlers will be able to check whether the
> caller actually set (using the argument size) the field vs. assigning it
> to zero. Separate macro can be provided for that.
>
> This will be easier for applications as well since there is no longer the
> problem of setting the reserved fields zero, or at least it is a lesser
> problem.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>

> ---
> drivers/media/media-device.c | 56 ++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 51 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index 6f565a2..aa37520 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -384,22 +384,36 @@ static long copy_arg_to_user(void __user *uarg, void *karg, unsigned int cmd)
> /* Do acquire the graph mutex */
> #define MEDIA_IOC_FL_GRAPH_MUTEX BIT(0)
>
> -#define MEDIA_IOC_ARG(__cmd, func, fl, from_user, to_user) \
> +#define MEDIA_IOC_SZ_ARG(__cmd, func, fl, alt_sz, from_user, to_user) \
> [_IOC_NR(MEDIA_IOC_##__cmd)] = { \
> .cmd = MEDIA_IOC_##__cmd, \
> .fn = (long (*)(struct media_device *, void *))func, \
> .flags = fl, \
> + .alt_arg_sizes = alt_sz, \
> .arg_from_user = from_user, \
> .arg_to_user = to_user, \
> }
>
> -#define MEDIA_IOC(__cmd, func, fl) \
> - MEDIA_IOC_ARG(__cmd, func, fl, copy_arg_from_user, copy_arg_to_user)
> +#define MEDIA_IOC_ARG(__cmd, func, fl, from_user, to_user) \
> + MEDIA_IOC_SZ_ARG(__cmd, func, fl, NULL, from_user, to_user)
> +
> +#define MEDIA_IOC_SZ(__cmd, func, fl, alt_sz) \
> + MEDIA_IOC_SZ_ARG(__cmd, func, fl, alt_sz, \
> + copy_arg_from_user, copy_arg_to_user)
> +
> +#define MEDIA_IOC(__cmd, func, fl) \
> + MEDIA_IOC_ARG(__cmd, func, fl, \
> + copy_arg_from_user, copy_arg_to_user)
>
> /* the table is indexed by _IOC_NR(cmd) */
> struct media_ioctl_info {
> unsigned int cmd;
> unsigned short flags;
> + /*
> + * Sizes of the alternative arguments. If there are none, this
> + * pointer is NULL.
> + */
> + const unsigned short *alt_arg_sizes;
> 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);
> @@ -413,11 +427,40 @@ static const struct media_ioctl_info ioctl_info[] = {
> MEDIA_IOC(G_TOPOLOGY, media_device_get_topology, MEDIA_IOC_FL_GRAPH_MUTEX),
> };
>
> +#define MASK_IOC_SIZE(cmd) \
> + ((cmd) & ~(_IOC_SIZEMASK << _IOC_SIZESHIFT))
> +
> static inline long is_valid_ioctl(const struct media_ioctl_info *info,
> unsigned int cmd)
> {
> - return (_IOC_NR(cmd) >= ARRAY_SIZE(ioctl_info)
> - || info[_IOC_NR(cmd)].cmd != cmd) ? -ENOIOCTLCMD : 0;
> + const unsigned short *alt_arg_sizes;
> +
> + if (_IOC_NR(cmd) >= ARRAY_SIZE(ioctl_info))
> + return -ENOIOCTLCMD;
> +
> + info += _IOC_NR(cmd);
> +
> + if (info->cmd == cmd)
> + return 0;
> +
> + /*
> + * Verify that the size-dependent patch of the IOCTL command
> + * matches and that the size does not exceed the principal
> + * argument size.
> + */
> + if (MASK_IOC_SIZE(info->cmd) != MASK_IOC_SIZE(cmd)
> + || _IOC_SIZE(info->cmd) < _IOC_SIZE(cmd))
> + return -ENOIOCTLCMD;
> +
> + alt_arg_sizes = info->alt_arg_sizes;
> + if (!alt_arg_sizes)
> + return -ENOIOCTLCMD;
> +
> + for (; *alt_arg_sizes; alt_arg_sizes++)
> + if (_IOC_SIZE(cmd) == *alt_arg_sizes)
> + return 0;
> +
> + return -ENOIOCTLCMD;
> }
>
> static long __media_device_ioctl(
> @@ -448,6 +491,9 @@ static long __media_device_ioctl(
> goto out_free;
> }
>
> + /* Set the rest of the argument struct to zero */
> + memset(karg + _IOC_SIZE(cmd), 0, _IOC_SIZE(info->cmd) - _IOC_SIZE(cmd));
> +
> if (info->flags & MEDIA_IOC_FL_GRAPH_MUTEX)
> mutex_lock(&dev->graph_mutex);
>
>