Re: [PATCH 0/7 v3] block: Add config option to not allow writing to mounted devices

[Jens Axboe <axboe@kernel.dk>]

On 11/1/23 11:43 AM, Jan Kara wrote:
> Hello!
> 
> This is the third version of the patches to add config option to not allow
> writing to mounted block devices. The new API for block device opening has been
> merged so hopefully this patchset can progress towards being merged. We face
> some issues with necessary btrfs changes (review bandwidth) so this series is
> modified to enable restricting of writes for all other filesystems. Once btrfs
> can merge necessary device scanning changes, enabling the support for
> restricting writes for it is trivial.
> 
> For motivation why restricting writes to mounted block devices is interesting
> see patch 3/7. I've been testing the patches more extensively and I've found
> couple of things that get broken by disallowing writes to mounted block
> devices:
> 
> 1) "mount -o loop" gets broken because util-linux keeps the loop device open
>    read-write when attempting to mount it. Hopefully fixable within util-linux.
> 2) resize2fs online resizing gets broken because it tries to open the block
>    device read-write only to call resizing ioctl. Trivial to fix within
>    e2fsprogs.
> 3) Online e2label will break because it directly writes to the ext2/3/4
>    superblock while the FS is mounted to set the new label.  Ext4 driver
>    will have to implement the SETFSLABEL ioctl() and e2label will have
>    to use it, matching what happens for online labelling of btrfs and
>    xfs.
> 
> Likely there will be other breakage I didn't find yet but overall the breakage
> looks minor enough that the option might be useful. Definitely good enough
> for syzbot fuzzing and likely good enough for hardening of systems with
> more tightened security.

For the series:

Reviewed-by: Jens Axboe <axboe@kernel.dk>

-- 
Jens Axboe