[Parted-maintainers] Bug#762236: parted: [kfreebsd] use of kern.geom.debugflags is unsafe

[Steven Chamberlain]

On 09:11, Phillip Susi wrote:
> Umm... it seems to me that if you open your disk O_RDWR, for instance,
> to update your boot loader, while you have a partition on the disk
> mounted, and the kernel destroys an actively mounted partition device,
> then the kernel is very, very broken...

Strangely, the GRUB install step doesn't seem to trigger this...  I
can't remember if I was using GPT.

A mere dd if=/dev/null bs=512 of=/dev/ada triggers it.  (No actual
blocks written).  But to open that O_RDWR when there are mounted
filesystems, requires kern.geom.debugflags to enable "foot shooting"
mode first.

I've only confirmed that it affects ZFS so far, with kfreebsd 10.1,
but I can see other partitions being detached / re-attached on
MEDIACHANGE.

> As for the performance implications, yes, parted should not be using
> O_RDWR when it do doesn't need it and does take care not to on linux.

OK I'll look into this, as we probably should be doing the same.

Regards,
-- 
Steven Chamberlain
steven at pyro.eu.org