Re: [PATCH] staging/android: refactor SYNC_IOC_FILE_INFO

[Gustavo Padovan]

Hi Maarten,

2016-02-29 Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>:

> 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.

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@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);

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?

	Gustavo