Re: [PATCH] staging/android: refactor SYNC_IOC_FILE_INFO

[Maarten Lankhorst]

Op 26-02-16 om 22:00 schreef Gustavo Padovan:
> From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
>
> Change SYNC_IOC_FILE_INFO behaviour to avoid future API breaks and
> optimize buffer allocation. In the new approach the ioctl needs to be called
> twice to retrieve the array of fence_infos pointed by info->sync_fence_info.
>
> The first call should pass num_fences = 0, the kernel will then fill
> info->num_fences. Userspace receives back the number of fences and
> allocates a buffer size num_fences * sizeof(struct sync_fence_info) on
> info->sync_fence_info.
>
> It then call the ioctl again passing num_fences received in info->num_fences.
> The kernel checks if info->num_fences > 0 and if yes it fill
> info->sync_fence_info with an array containing all fence_infos.
>
> info->len now represents the length of the buffer sync_fence_info points
> to. Also, info->sync_fence_info was converted to __u64 pointer.
>
> An example userspace code would be:
>
> 	struct sync_file_info *info;
> 	int err, size, num_fences;
>
> 	info = malloc(sizeof(*info));
>
> 	memset(info, 0, sizeof(*info));
>
> 	err = ioctl(fd, SYNC_IOC_FILE_INFO, info);
> 	num_fences = info->num_fences;
>
> 	if (num_fences) {
> 		memset(info, 0, sizeof(*info));
Would this memset still be needed if we didn't check for nulls in info->status and info->name ?

Seems to me that it could be skipped in that case.
> 		size = sizeof(struct sync_fence_info) * num_fences;
> 		info->len = size;
> 		info->num_fences = num_fences;
> 		info->sync_fence_info = (uint64_t) calloc(num_fences,
> 							  sizeof(struct sync_fence_info));
>
> 		err = ioctl(fd, SYNC_IOC_FILE_INFO, info);
> 	}
>
> v2: fix fence_info memory leak
>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
> ---
>  drivers/staging/android/sync.c      | 52 +++++++++++++++++++++++++++++--------
>  drivers/staging/android/uapi/sync.h |  9 +++----
>  2 files changed, 45 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
> index dc5f382..2379f23 100644
> --- a/drivers/staging/android/sync.c
> +++ b/drivers/staging/android/sync.c
> @@ -502,21 +502,22 @@ static int sync_fill_fence_info(struct fence *fence, void *data, int size)
>  static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>  					unsigned long arg)
>  {
> -	struct sync_file_info *info;
> +	struct sync_file_info in, *info;
> +	struct sync_fence_info *fence_info = NULL;
>  	__u32 size;
>  	__u32 len = 0;
= 0 unneeded.
>  	int ret, i;
>  
> -	if (copy_from_user(&size, (void __user *)arg, sizeof(size)))
> +	if (copy_from_user(&in, (void __user *)arg, sizeof(*info)))
>  		return -EFAULT;
>  
> -	if (size < sizeof(struct sync_file_info))
> -		return -EINVAL;
> +	if (in.status || strcmp(in.name, "\0"))
> +		return -EFAULT;
These members always get written by the fence ioctl, I'm not sure it adds value to have them explicitly zero'd out by userspace.
> -	if (size > 4096)
> -		size = 4096;
> +	if (in.num_fences && !in.sync_fence_info)
> +		return -EFAULT;
This check is unneeded, it will happen in the copy_to_user call anyway.
> -	info = kzalloc(size, GFP_KERNEL);
> +	info = kzalloc(sizeof(*info), GFP_KERNEL);
>  	if (!info)
>  		return -ENOMEM;
>  
> @@ -525,14 +526,33 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>  	if (info->status >= 0)
>  		info->status = !info->status;
>  
> -	info->num_fences = sync_file->num_fences;
> +	/*
> +	 * Passing num_fences = 0 means that userspace want to know how
> +	 * many fences are in the sync_file to be able to allocate a buffer to
> +	 * fit all sync_fence_infos and call the ioctl again with the buffer
> +	 * assigned to info->sync_fence_info. The second call pass the
> +	 * num_fences value received in the first call.
> +	 */
> +	if (!in.num_fences)
> +		goto no_fences;
> +
> +	size = sync_file->num_fences * sizeof(*fence_info);
> +	if (in.len != size) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
Maybe check for in.len < size, and set set to size?


> -	len = sizeof(struct sync_file_info);
> +	fence_info = kzalloc(size, GFP_KERNEL);
> +	if (!fence_info) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
>  
>  	for (i = 0; i < sync_file->num_fences; ++i) {
>  		struct fence *fence = sync_file->cbs[i].fence;
>  
> -		ret = sync_fill_fence_info(fence, (u8 *)info + len, size - len);
> +		ret = sync_fill_fence_info(fence, (u8 *)fence_info + len,
> +					   size - len);
>  
>  		if (ret < 0)
>  			goto out;
> @@ -540,14 +560,24 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>  		len += ret;
>  	}
>  
> +	if (copy_to_user((void __user *)in.sync_fence_info, fence_info, size)) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
> +
>  	info->len = len;
> +	info->sync_fence_info = (__u64) in.sync_fence_info;
> +
> +no_fences:
> +	info->num_fences = sync_file->num_fences;
>  
> -	if (copy_to_user((void __user *)arg, info, len))
> +	if (copy_to_user((void __user *)arg, info, sizeof(*info)))
>  		ret = -EFAULT;
>  	else
>  		ret = 0;
>  
>  out:
> +	kfree(fence_info);
>  	kfree(info);
>  
>  	return ret;
> diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
> index f0b41ce..9aad623 100644
> --- a/drivers/staging/android/uapi/sync.h
> +++ b/drivers/staging/android/uapi/sync.h
> @@ -42,21 +42,20 @@ struct sync_fence_info {
>  
>  /**
>   * struct sync_file_info - data returned from fence info ioctl
> - * @len:	ioctl caller writes the size of the buffer its passing in.
> - *		ioctl returns length of sync_file_info returned to
> - *		userspace including pt_info.
>   * @name:	name of fence
>   * @status:	status of fence. 1: signaled 0:active <0:error
>   * @num_fences	number of fences in the sync_file
> + * @len:	ioctl caller writes the size of the buffer its passing in.
> + *		ioctl returns length of all fence_infos summed.
>   * @sync_fence_info: array of sync_fence_info for every fence in the sync_file
>   */
>  struct sync_file_info {
> -	__u32	len;
>  	char	name[32];
>  	__s32	status;
>  	__u32	num_fences;
> +	__u32	len;
>  
> -	__u8	sync_fence_info[0];
> +	__u64	sync_fence_info;
>  };
>  
>  #define SYNC_IOC_MAGIC		'>'
Not sure if len adds anything here, userspace knows to allocate num_fences * sizeof(struct sync_fence_info);

It could probably be removed since num_fences would do the same.

~Maarten