| Message ID | 20240826001624.188581-1-gpiccoli@igalia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V4] Documentation: Document the kernel flag bdev_allow_write_mounted | expand |
On Sun 25-08-24 21:15:11, 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@acm.org> > Cc: Darrick J. Wong <djwong@kernel.org> > Cc: Jan Kara <jack@suse.cz> > Cc: Jens Axboe <axboe@kernel.dk> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> > --- > > V4: More improvements in the wording (thanks Jens and Darrick!) > > V3 link: https://lore.kernel.org/r/20240823180635.86163-1-gpiccoli@igalia.com > > > 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..d521d444a35c 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 to open a block device for ^^ a mounted block device Otherwise looks good so feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > + writing, i.e., allow / disallow writes that bypass > + the 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. > > -- > 2.46.0 >
On 28/08/2024 10:26, Jan Kara wrote: > [...] >> --- 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 to open a block device for > ^^ a mounted block device > > Otherwise looks good so feel free to add: > > Reviewed-by: Jan Kara <jack@suse.cz> > Thanks! Just sent the v5.
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 09126bb8cc9f..d521d444a35c 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 to open a block device for + writing, i.e., allow / disallow writes that bypass + the 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.
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@acm.org> Cc: Darrick J. Wong <djwong@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> --- V4: More improvements in the wording (thanks Jens and Darrick!) V3 link: https://lore.kernel.org/r/20240823180635.86163-1-gpiccoli@igalia.com Documentation/admin-guide/kernel-parameters.txt | 12 ++++++++++++ 1 file changed, 12 insertions(+)