On Fri, Aug 23, 2024 at 12:17:54PM -0600, Jens Axboe wrote:
> On 8/23/24 12:05 PM, Guilherme G. Piccoli wrote:
> > Commit ed5cc702d311 ("block: Add config option to not allow writing to mounted
> > devices") added a Kconfig option along with a kernel command-line tuning to
> > control writes to mounted block devices, as a means to deal with fuzzers like
> > Syzkaller, that provokes kernel crashes by directly writing on block devices
> > bypassing the filesystem (so the FS has no awareness and cannot cope with that).
> >
> > The patch just missed adding such kernel command-line option to the kernel
> > documentation, so let's fix that.
> >
> > Cc: Bart Van Assche <bvanassche@xxxxxxx>
> > Cc: Darrick J. Wong <djwong@xxxxxxxxxx>
> > Cc: Jan Kara <jack@xxxxxxx>
> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
> > ---
> >
> > V3: Dropped reference to page cache (thanks Bart!).
> >
> > V2 link: https://lore.kernel.org/r/20240823142840.63234-1-gpiccoli@xxxxxxxxxx
> >
> >
> > Documentation/admin-guide/kernel-parameters.txt | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 09126bb8cc9f..58b9455baf4a 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -517,6 +517,18 @@
> > Format: <io>,<irq>,<mode>
> > See header of drivers/net/hamradio/baycom_ser_hdx.c.
> >
> > + bdev_allow_write_mounted=
> > + Format: <bool>
> > + Control the ability of directly writing to mounted block
>
> Since we're nit picking...
>
> Control the ability to directly write [...]
>
> The directly may be a bit confusing ("does it mean O_DIRECT?"), so maybe
> just
>
> Control the ability to write [...]
>
> would be better and more clear.
"Control the ability to open a block device for writing."
Since that's what it actually does, right?
--D
> > + devices, i.e., allow / disallow writes that bypasses the
>
> Since we're nit picking, s/bypasses/bypass
>
> > + FS. This was implemented as a means to prevent fuzzers
> > + from crashing the kernel by overwriting the metadata
> > + underneath a mounted FS without its awareness. This
> > + also prevents destructive formatting of mounted
> > + filesystems by naive storage tooling that don't use
> > + O_EXCL. Default is Y and can be changed through the
> > + Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED.
> > +
> > bert_disable [ACPI]
> > Disable BERT OS support on buggy BIOSes.
>
> --
> Jens Axboe
>
