On Fri, Jul 21, 2017 at 01:29:07PM -0400, [email protected] wrote:
> From: Josef Bacik <[email protected]>
> 
> We need to use file->private_data for readdir on directories, so just
> don't allow user space transactions on directories.
> 
> Signed-off-by: Josef Bacik <[email protected]>
> ---
>  fs/btrfs/ioctl.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index bedeec6..ddb3811 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3968,6 +3968,9 @@ static long btrfs_ioctl_trans_start(struct file *file)
>       struct btrfs_trans_handle *trans;
>       int ret;
>  
> +     if (S_ISDIR(inode->i_mode))
> +             return -EINVAL;

You can't do this, starting a transaction on a directory needs to work.
The most natural way to run the ioctl is on the mount point.

The file private data would need to be able to hold multipe values, so
you can add

struct btrfs_inode {
        ...
        struct priv_data {
                void *for_readdir;
                void *for_tranc_ioctl;
        };
        ...
};

then set file->file_private = &btrfs_inode->priv_data; and update all
uses to check for the embedded pointers.

> +
>       ret = -EPERM;
>       if (!capable(CAP_SYS_ADMIN))
>               goto out;
> -- 
> 2.7.4
> 
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