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Piccoli" , linux-doc@vger.kernel.org Cc: corbet@lwn.net, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, Bart Van Assche , "Darrick J. Wong" , Jan Kara References: <20240823180635.86163-1-gpiccoli@igalia.com> Content-Language: en-US From: Jens Axboe In-Reply-To: <20240823180635.86163-1-gpiccoli@igalia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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 > Cc: Darrick J. Wong > Cc: Jan Kara > Signed-off-by: Guilherme G. Piccoli > --- > > V3: Dropped reference to page cache (thanks Bart!). > > V2 link: https://lore.kernel.org/r/20240823142840.63234-1-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..58b9455baf4a 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -517,6 +517,18 @@ > Format: ,, > See header of drivers/net/hamradio/baycom_ser_hdx.c. > > + bdev_allow_write_mounted= > + Format: > + 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. > + 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