Re: [RFC] fuse: disable support for file handle when FUSE_EXPORT_SUPPORT not configured

[Jingbo Xu <jefflexu@linux.alibaba.com>]

On 1/23/24 6:17 PM, Amir Goldstein wrote:
> If you somehow find a way to mitigate the regression for NFS export of
> old fuse servers (maybe an opt-in Kconfig?), your patch is also going to
> regress AT_HANDLE_FID functionality, which can be used by fanotify to
> monitor fuse.
> 
> AT_HANDLE_FID flag to name_to_handle_at(2) means that
> open_by_handle_at(2) is not supposed to be called on that fh.
> 
> The correct way to deal with that would be something like this:
> 
> +static const struct export_operations fuse_fid_operations = {
> +       .encode_fh      = fuse_encode_fh,
> +};
> +
>  static const struct export_operations fuse_export_operations = {
>         .fh_to_dentry   = fuse_fh_to_dentry,
>         .fh_to_parent   = fuse_fh_to_parent,
> @@ -1529,12 +1533,16 @@ static void fuse_fill_attr_from_inode(struct
> fuse_attr *attr,
> 
>  static void fuse_sb_defaults(struct super_block *sb)
>  {
> +       struct fuse_mount *fm = get_fuse_mount_super(sb);
> +
>         sb->s_magic = FUSE_SUPER_MAGIC;
>         sb->s_op = &fuse_super_operations;
>         sb->s_xattr = fuse_xattr_handlers;
>         sb->s_maxbytes = MAX_LFS_FILESIZE;
>         sb->s_time_gran = 1;
> -       sb->s_export_op = &fuse_export_operations;
> +       if (fm->fc->export_support)
> +               sb->s_export_op = &fuse_export_operations;
> +       else
> +               sb->s_export_op = &fuse_fid_operations;
>         sb->s_iflags |= SB_I_IMA_UNVERIFIABLE_SIGNATURE;
>         if (sb->s_user_ns != &init_user_ns)
>                 sb->s_iflags |= SB_I_UNTRUSTED_MOUNTER;
> 
> ---
> 
> This would make name_to_handle_at() without AT_HANDLE_FID fail
> and name_to_handle_at() with AT_HANDLE_FID to succeed as it should.
> 

Oh I didn't notice this.  Many thanks!


-- 
Thanks,
Jingbo