Enable checks on linked list manipulation
Ensures the running kernel is built with CONFIG_DEBUG_LIST=y, adding sanity checks to linked-list manipulation that catch corruption before it can be exploited.
Checked against the resolved running state (e.g. sshd -T, sysctl, systemctl show), catches drop-ins and Includes a file read would miss. Caveat: runtime ≠ persistence; a value correct now may not survive a reboot.
Pavois asserts the effective configuration, the live, resolved state, not a file. File-based scanners (OVAL/SCAP, Lynis) miss Includes, drop-ins and runtime defaults; this check sees what is actually applied.
A mapping is a cross-reference to where each standard places this requirement, anchored and cross-validated, not a claim of equivalence. A passing check is evidence toward these references, how to read it.
Why this rule matters
CONFIG_DEBUG_LIST=y adds integrity checks to the kernel's intrusive linked-list operations (list_add, list_del, …), validating the prev/next pointers before each manipulation. Linked-list corruption, often via race conditions or use-after-free, is a classic exploitation primitive: a crafted overwrite of list pointers can give an attacker an arbitrary write. These checks detect the inconsistency and abort the operation (e.g. preventing exploits like the list-corruption race CVE-2017-1661), turning a potential write primitive into a safe failure.
What Pavois checks
Pavois reads the build-time config of the running kernel via /boot/config-$(uname -r) (fallback /proc/config.gz) and asserts CONFIG_DEBUG_LIST=y. Keying on uname -r matches the exact booted image, more reliable than reading a random /boot/config-*. This option underpins CONFIG_BUG_ON_DATA_CORRUPTION, which escalates a detected list corruption to a hard BUG().
describe command("C=/boot/config-$(uname -r); if [ -r \"$C\" ]; then cat \"$C\"; elif zcat /proc/config.gz 2>/dev/null | head -1 | grep -q .; then zcat /proc/config.gz; else echo PAVOIS_NO_KERNEL_CONFIG; fi | grep -E '^(CONFIG_DEBUG_LIST=|PAVOIS_NO_KERNEL_CONFIG)'") do
its('stdout') { should_not match(/PAVOIS_NO_KERNEL_CONFIG/) }
its('stdout') { should match(/^CONFIG_DEBUG_LIST=y$/) }
endHow to verify it is applied
Run grep -h '^CONFIG_DEBUG_LIST=' /boot/config-$(uname -r) (or zcat /proc/config.gz | grep DEBUG_LIST). Expected: CONFIG_DEBUG_LIST=y.
Inspect & investigate
Static kernel build option, no dedicated log. Inspect with zcat /proc/config.gz | grep DEBUG_LIST or grep DEBUG_LIST /boot/config-$(uname -r). When a list-corruption check trips at runtime, the warning/oops with a backtrace appears in dmesg and journalctl -k.
Remediation
No automated remediation is shipped: this is a kernel compile-time option. Apply it by booting a kernel built with CONFIG_DEBUG_LIST=y (a hardened or security-oriented kernel), or rebuild the kernel. pavois harden apply cannot change it.
Pavois applies this with its own harden engine, the plan below, not a shell script:
| resource | kernel_build |
|---|
pavois harden plan localwhere the target is local, a user@host SSH alias, or a container , Docs
Impact & precautions
Risk if disabled: linked-list corruption, a common path to an arbitrary kernel write, goes undetected and can be exploited for privilege escalation.
Precautions before changing it: the checks add a small per-operation overhead but no functional risk, and most distribution kernels already enable them. Changing kernels requires a reboot; keep the previous kernel in GRUB as a fallback and validate boot on a console.
Standards mapping
| Standard | Reference | Type | Version | Confidence |
|---|---|---|---|---|
| ANSSI BP-028 | R16 | direct | 2.0 | high |
Each reference is a cross-reference anchored in the upstream benchmark and cross-validated against the SCAP Security Guide and ansible-lockdown, not a claim of equivalence. Direct = a prescriptive, line-level requirement; supporting = an abstract control family (NIST) the check provides evidence toward. How to read a mapping.