Re: [PATCH RFC 40/41] erofs: refuse files on pseudo filesystems as backing files

[Alexander Mikhalitsyn <alex@xxxxxxxxxxxx>]

On Tue, 2026-11-10 at 10:14 +0100, Christian Brauner wrote:
> File-backed mounts take any regular file as the image and the same
> goes
> for the extra devices of such a mount. erofs reads them with the
> credentials of the mounter so this doesn't hand out anything the
> mounter
> couldn't read anyway. But files on pseudo filesystems aren't images.
> Refuse them just like loop does.
> 
> Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>

Reviewed-by: Alexander Mikhalitsyn <alex@xxxxxxxxxxxx>

> ---
>  fs/erofs/super.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index ce05557bd998..980d5fc2b576 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -158,7 +158,8 @@ static int erofs_init_device(struct erofs_buf
> *buf, struct super_block *sb,
>               if (!erofs_is_fileio_mode(sbi)) {
>                       dif->dax_dev =
> fs_dax_get_by_bdev(file_bdev(file),
>                                       &dif->dax_part_off, NULL,
> NULL);
> -             } else if (!S_ISREG(file_inode(file)->i_mode)) {
> +             } else if (!S_ISREG(file_inode(file)->i_mode) ||
> +                        file_is_pseudo(file)) {
>                       fput(file);
>                       return -EINVAL;
>               }
> @@ -835,6 +836,9 @@ static int erofs_file_get_tree(struct fs_context
> *fc)
>  {
>       struct erofs_sb_info *sbi = fc->s_fs_info;
>  
> +     if (file_is_pseudo(sbi->dif0.file))
> +             return invalfc(fc, "source is on a pseudo
> filesystem");
> +
>       if (!test_opt(&sbi->opt, SUPERBLOCK_SHARE))
>               return get_tree_nodev(fc, erofs_fc_fill_super);
>