[PATCH v3 0/5] Landlock: IOCTL support

[Mickaël Salaün]

On Mon, Aug 14, 2023 at 07:28:11PM +0200, Günther Noack wrote:
> Hello!
> 
> These patches add simple ioctl(2) support to Landlock.
> 

[...]

> How we arrived at the list of always-permitted IOCTL commands
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> To decide which IOCTL commands should be blanket-permitted I went through the
> list of IOCTL commands mentioned in fs/ioctl.c and looked at them individually
> to understand what they are about.  The following list is my conclusion from
> that.
> 
> We should always allow the following IOCTL commands:
> 
>  * FIOCLEX, FIONCLEX - these work on the file descriptor and manipulate the
>    close-on-exec flag
>  * FIONBIO, FIOASYNC - these work on the struct file and enable nonblocking-IO
>    and async flags
>  * FIONREAD - get the number of bytes available for reading (the implementation
>    is defined per file type)

I think we should treat FIOQSIZE like FIONREAD, i.e. check for
LANDLOCK_ACCESS_FS_READ_FILE as explain in my previous message.
Tests should then rely on something else.

[...]

> Changes
> ~~~~~~~
> 
> V3:
>  * always permit the IOCTL commands FIOCLEX, FIONCLEX, FIONBIO, FIOASYNC and
>    FIONREAD, independent of LANDLOCK_ACCESS_FS_IOCTL
>  * increment ABI version in the same commit where the feature is introduced
>  * testing changes
>    * use FIOQSIZE instead of TTY IOCTL commands
>      (FIOQSIZE works with regular files, directories and memfds)
>    * run the memfd test with both Landlock enabled and disabled
>    * add a test for the always-permitted IOCTL commands