[PATCH ghak10 v5 0/2] audit: Log modifying adjtimex(2) calls

From: Ondrej Mosnacek
Date: Fri Aug 24 2018 - 08:00:29 EST

This patchset implements more detailed auditing of the adjtimex(2)
syscall in order to make it possible to:
a) distinguish modifying vs. read-only calls in the audit log
b) reconstruct from the audit log what changes were made and how they
have influenced the system clock

The main motivation is to be able to detect an adversary that tries to
confuse the audit timestamps by changing system time via adjtimex(2),
but at the same time avoid flooding the audit log with records of benign
read-only adjtimex(2) calls.

The current version of the patchset logs the following changes:
- direct injection of timekeeping offset
- adjustment of timekeeping's TAI offset
- NTP value adjustments:
- time_offset
- time_freq
- time_status
- time_adjust
- tick_usec

Changes to the following NTP values are not logged, as they are not
important for security:
- time_maxerror
- time_esterror
- time_constant

Audit kernel GitHub issue: https://github.com/linux-audit/audit-kernel/issues/10

Changes in v5:
- Dropped logging of some less important changes and update commit messages
- No longer mark the patchset as RFC

v4: https://www.redhat.com/archives/linux-audit/2018-August/msg00023.html
Changes in v4:
- Squashed first two patches into one
- Renamed ADJNTPVAL's "type" field to "op" to align with audit record
- Minor commit message editing
- Cc timekeeping/NTP people for feedback

v3: https://www.redhat.com/archives/linux-audit/2018-July/msg00001.html
Changes in v3:
- Switched to separate records for each variable
- Both old and new value is now reported for each change
- Injecting offset is reported via a separate record (since this
offset consists of two values and is added directly to the clock,
i.e. it doesn't make sense to log old and new value)
- Added example records produced by chronyd -q (see the commit message
of the last patch)

v2: https://www.redhat.com/archives/linux-audit/2018-June/msg00114.html
Changes in v2:
- The audit_adjtime() function has been modified to only log those
fields that contain values that are actually used, resulting in more
compact records.
- The audit_adjtime() call has been moved to do_adjtimex() in
- Added an additional patch (for review) that simplifies the detection
if the syscall is read-only.

v1: https://www.redhat.com/archives/linux-audit/2018-June/msg00095.html

Ondrej Mosnacek (2):
audit: Add functions to log time adjustments
timekeeping/ntp: Audit clock/NTP params adjustments

include/linux/audit.h | 21 +++++++++++++++++++++
include/uapi/linux/audit.h | 2 ++
kernel/auditsc.c | 15 +++++++++++++++
kernel/time/ntp.c | 38 ++++++++++++++++++++++++++++++--------
kernel/time/timekeeping.c | 3 +++
5 files changed, 71 insertions(+), 8 deletions(-)