May 26, 2018

Tool to preload kernel iconv charset tables

On FreeBSD, it’s possible to allow plain users to mount filesystems without using su or sudo. This is enabled via vfs.usermount sysctl. However, if file name conversion is used when mounting a filesystem, in most cases mount will fail with `mount_XXX XXX_iconv Operation not permitted denied’ error. This is caused by the fact that character set conversion tables need to be loaded into kernel, but, apart from mounting, that’s not allowed to plain users, because charset tables are large enough to initiate a denial of service by filling kernel memory with many tables.

This utility allows you to load only specific charset tables into kernel, so usermounts with file name conversions won’t fail and in the same time it’s not possible to bring the system down by filling kernel memory.

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