Re: [PATCH] staging/android: refactor SYNC_IOC_FILE_INFO

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 29-02-16 om 23:08 schreef Gustavo Padovan:
> Hi Maarten,
>
> 2016-02-29 Maarten Lankhorst <maarten.lankhorst@linux.intel.com>:
>
>> Op 26-02-16 om 22:00 schreef Gustavo Padovan:
>>> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
>>>
>>> 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.
> Yes, I agree.
>
>>> 		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@collabora.co.uk>
>>> ---
>>>  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);
> I think of len being useful if we decide to extend struct sync_fence_info in
> the future, so we may use len to help discover the size of each
> sync_fence_info. What do you think?
>
I don't think you could extend it arbitrarily, you could make userspace pass a flag to indicate the struct is extended, so kernel space can choose
whether to use the bigger size struct or not.

something like sync_file_info.flags = FENCE_INFO_V2; -- kernel can reject with -EINVAL if unsupported, or fill in a v2 struct.

~Maarten
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