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dm-verity signals integrity violations by returning I/O errors
to user space. To identify integrity violations by a controlling
instance, the kernel audit subsystem can be used to emit audit
events to user space. Analogous to dm-integrity, we also use the
dm-audit submodule allowing to emit audit events on verification
failures of metadata and data blocks as well as if max corrupted
errors are reached.
The construction and destruction of verity device mappings are
also relevant for auditing a system. Thus, those events are also
logged as audit events.
Tested by starting a container with the container manager (cmld) of
GyroidOS which uses a dm-verity protected rootfs image root.img mapped
to /dev/mapper/<uuid>-root. One block was manipulated in the
underlying image file and repeated reads of the verity device were
performed again until the max corrupted errors is reached, e.g.:
dd if=/dev/urandom of=root.img bs=512 count=1 seek=1000
for i in range {1..101}; do \
dd if=/dev/mapper/<uuid>-root of=/dev/null bs=4096 \
count=1 skip=1000 \
done
The resulting audit log looks as follows:
type=DM_CTRL msg=audit(1677618791.876:962):
module=verity op=ctr ppid=4876 pid=29102 auid=0 uid=0 gid=0
euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=44
comm="cmld" exe="/usr/sbin/cml/cmld" subj=unconfined
dev=254:3 error_msg='success' res=1
type=DM_EVENT msg=audit(1677619463.786:1074): module=verity
op=verify-data dev=7:0 sector=1000 res=0
...
type=DM_EVENT msg=audit(1677619596.727:1162): module=verity
op=verify-data dev=7:0 sector=1000 res=0
type=DM_EVENT msg=audit(1677619596.731:1163): module=verity
op=max-corrupted-errors dev=254:3 sector=? res=0
Signed-off-by: Michael Weiß <michael.weiss@aisec.fraunhofer.de>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.