On Oct  4, 2023 Fan Wu [off-list ref] wrote:

Users of IPE require a way to identify when and why an operation fails,
allowing them to both respond to violations of policy and be notified
of potentially malicious actions on their systems with respect to IPE
itself.

This patch introduces 3 new audit events.

AUDIT_IPE_ACCESS(1420) indicates the result of an IPE policy evaluation
of a resource.
AUDIT_IPE_CONFIG_CHANGE(1421) indicates the current active IPE policy
has been changed to another loaded policy.
AUDIT_IPE_POLICY_LOAD(1422) indicates a new IPE policy has been loaded
into the kernel.

This patch also adds support for success auditing, allowing users to
identify why an allow decision was made for a resource. However, it is
recommended to use this option with caution, as it is quite noisy.

Here are some examples of the new audit record types:

AUDIT_IPE_ACCESS(1420):

    audit: AUDIT1420 path="/root/vol/bin/hello" dev="sda"
      ino=3897 rule="op=EXECUTE boot_verified=TRUE action=ALLOW"

    audit: AUDIT1420 path="/mnt/ipe/bin/hello" dev="dm-0"
      ino=2 rule="DEFAULT action=DENY"

    audit: AUDIT1420 path="/tmp/tmpdp2h1lub/deny/bin/hello" dev="tmpfs"
      ino=131 rule="DEFAULT action=DENY"

The above three records were generated when the active IPE policy only
allows binaries from the initial booted drive(sda) to run. The three
identical `hello` binary were placed at different locations, only the
first hello from sda was allowed.

Field path followed by the file's path name.

Field dev followed by the device name as found in /dev where the file is
from.
Note that for device mappers it will use the name `dm-X` instead of
the name in /dev/mapper.
For a file in a temp file system, which is not from a device, it will use
`tmpfs` for the field.
The implementation of this part is following another existing use case
LSM_AUDIT_DATA_INODE in security/lsm_audit.c

Field ino followed by the file's inode number.

Field rule followed by the IPE rule made the access decision. The whole
rule must be audited because the decision is based on the combination of
all property conditions in the rule.

Along with the syscall audit event, user can know why a blocked
happened. For example:

    audit: AUDIT1420 path="/mnt/ipe/bin/hello" dev="dm-0"
      ino=2 rule="DEFAULT action=DENY"
    audit[1956]: SYSCALL arch=c000003e syscall=59
      success=no exit=-13 a0=556790138df0 a1=556790135390 a2=5567901338b0
      a3=ab2a41a67f4f1f4e items=1 ppid=147 pid=1956 auid=4294967295 uid=0
      gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts0
      ses=4294967295 comm="bash" exe="/usr/bin/bash" key=(null)

The above two records showed bash used execve to run "hello" and got
blocked by IPE. Note that the IPE records are always prior to a SYSCALL
record.

AUDIT_IPE_CONFIG_CHANGE(1421):

    audit: AUDIT1421
      old_active_pol_name="Allow_All" old_active_pol_version=0.0.0
      old_policy_digest=sha256:E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649
      new_active_pol_name="boot_verified" new_active_pol_version=0.0.0
      new_policy_digest=sha256:820EEA5B40CA42B51F68962354BA083122A20BB846F
      auid=4294967295 ses=4294967295 lsm=ipe res=1

The above record showed the current IPE active policy switch from
`Allow_All` to `boot_verified` along with the version and the hash
digest of the two policies. Note IPE can only have one policy active
at a time, all access decision evaluation is based on the current active
policy.
The normal procedure to deploy a policy is loading the policy to deploy
into the kernel first, then switch the active policy to it.

AUDIT_IPE_POLICY_LOAD(1422):

audit: AUDIT1422 policy_name="boot_verified" policy_version=0.0.0
policy_digest=sha256:820EEA5B40CA42B51F68962354BA083122A20BB846F26765076DD
auid=4294967295 ses=4294967295 lsm=ipe res=1

The above record showed a new policy has been loaded into the kernel
with the policy name, policy version and policy hash.

Signed-off-by: Deven Bowers <redacted>
Signed-off-by: Fan Wu <redacted>
---

v2:
  + Split evaluation loop, access control hooks,
    and evaluation loop from policy parser and userspace
    interface to pass mailing list character limit

v3:
  + Move ipe_load_properties to patch 04.
  + Remove useless 0-initializations
  + Prefix extern variables with ipe_
  + Remove kernel module parameters, as these are
    exposed through sysctls.
  + Add more prose to the IPE base config option
    help text.
  + Use GFP_KERNEL for audit_log_start.
  + Remove unnecessary caching system.
  + Remove comments from headers
  + Use rcu_access_pointer for rcu-pointer null check
  + Remove usage of reqprot; use prot only.
  + Move policy load and activation audit event to 03/12

v4:
  + Remove sysctls in favor of securityfs nodes
  + Re-add kernel module parameters, as these are now
    exposed through securityfs.
  + Refactor property audit loop to a separate function.

v5:
  + fix minor grammatical errors
  + do not group rule by curly-brace in audit record,
    reconstruct the exact rule.

v6:
  + No changes

v7:
  + Further split lsm creation, the audit system, the evaluation loop,
    and access control hooks into separate patches.
  + Further split audit system patch into two separate patches; one
    for include/uapi, and the usage of the new defines.
  + Split out the permissive functionality into another separate patch,
    for easier review.
  + Correct misuse of audit_log_n_untrusted string to audit_log_format
  + Use get_task_comm instead of comm directly.
  + Quote certain audit values
  + Remove unnecessary help text on choice options - these were
    previously
    idented at the wrong level
  + Correct a stale string constant (ctx_ns_enforce to ctx_enforce)

v8:

  + Change dependency for CONFIG_AUDIT to CONFIG_AUDITSYSCALL
  + Drop ctx_* prefix
  + Reuse, where appropriate, the audit fields from the field
    dictionary. This transforms:
      ctx_pathname  -> path
      ctx_ino       -> ino
      ctx_dev       -> dev

  + Add audit records and event examples to commit description.
  + Remove new_audit_ctx, replace with audit_log_start. All data that
    would provided by new_audit_ctx is already present in the syscall
    audit record, that is always emitted on these actions. The audit
    records should be correlated as such.
  + Change audit types:
    + AUDIT_TRUST_RESULT                -> AUDIT_IPE_ACCESS
      +  This prevents overloading of the AVC type.
    + AUDIT_TRUST_POLICY_ACTIVATE       -> AUDIT_MAC_CONFIG_CHANGE
    + AUDIT_TRUST_POLICY_LOAD           -> AUDIT_MAC_POLICY_LOAD
      + There were no significant difference in meaning between
        these types.

  + Remove enforcing parameter passed from the context structure
    for AUDIT_IPE_ACCESS.
    +  This field can be inferred from the SYSCALL audit event,
       based on the success field.

  + Remove all fields already captured in the syscall record. "hook",
    an IPE specific field, can be determined via the syscall field in
    the syscall record itself, so it has been removed.
      + ino, path, and dev in IPE's record refer to the subject of the
        syscall, while the syscall record refers to the calling process.

  + remove IPE prefix from policy load/policy activation events
  + fix a bug wherein a policy change audit record was not fired when
    updating a policy

v9:
  + Merge the AUDIT_IPE_ACCESS definition with the audit support commit
  + Change the audit format of policy load and switch
  + Remove the ipe audit kernel switch

v10:
  + Create AUDIT_IPE_CONFIG_CHANGE and AUDIT_IPE_POLICY_LOAD
  + Change field names per upstream feedback

v11:
  + Fix style issues
---
 include/uapi/linux/audit.h |   3 +
 security/ipe/Kconfig       |   2 +-
 security/ipe/Makefile      |   1 +
 security/ipe/audit.c       | 195 +++++++++++++++++++++++++++++++++++++
 security/ipe/audit.h       |  18 ++++
 security/ipe/eval.c        |  32 ++++--
 security/ipe/eval.h        |   8 ++
 security/ipe/fs.c          |  70 +++++++++++++
 security/ipe/policy.c      |   5 +
 9 files changed, 327 insertions(+), 7 deletions(-)
 create mode 100644 security/ipe/audit.c
 create mode 100644 security/ipe/audit.h

...

I would suggest taking the same approach for both @audit_op_names and
@audit_prop_names; either include the field name in the string array
for both or leave it out of both.

+/**
+ * audit_rule - audit an IPE policy rule approximation.
+ * @ab: Supplies a pointer to the audit_buffer to append to.
+ * @r: Supplies a pointer to the ipe_rule to approximate a string form for.
+ */
+static void audit_rule(struct audit_buffer *ab, const struct ipe_rule *r)
+{
+	const struct ipe_prop *ptr;
+
+	audit_log_format(ab, "rule=\"op=%s ", audit_op_names[r->op]);
+
+	list_for_each_entry(ptr, &r->props, next)
+		audit_log_format(ab, "%s ", audit_prop_names[ptr->type]);
+
+	audit_log_format(ab, "action=%s\"", ACTSTR(r->action));
+}
+
+/**
+ * ipe_audit_match - audit a match for IPE policy.
+ * @ctx: Supplies a pointer to the evaluation context that was used in the
+ *	 evaluation.
+ * @match_type: Supplies the scope of the match: rule, operation default,
+ *		global default.
+ * @act: Supplies the IPE's evaluation decision, deny or allow.
+ * @r: Supplies a pointer to the rule that was matched, if possible.
+ * @enforce: Supplies the enforcement/permissive state at the point
+ *	     the enforcement decision was made.
+ */

Does it make sense to move @match_type into the ipe_eval_ctx struct?

+void ipe_audit_match(const struct ipe_eval_ctx *const ctx,
+		     enum ipe_match match_type,
+		     enum ipe_action_type act, const struct ipe_rule *const r)
+{
+	struct inode *inode;
+	struct audit_buffer *ab;
+	const char *op = audit_op_names[ctx->op];
+
+	if (act != IPE_ACTION_DENY && !READ_ONCE(success_audit))
+		return;
+
+	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_IPE_ACCESS);
+	if (!ab)
+		return;
+
+	if (ctx->file) {
+		audit_log_d_path(ab, "path=", &ctx->file->f_path);
+		inode = file_inode(ctx->file);
+		if (inode) {
+			audit_log_format(ab, " dev=");
+			audit_log_untrustedstring(ab, inode->i_sb->s_id);
+			audit_log_format(ab, " ino=%lu ", inode->i_ino);
+		}
+	}
+
+	if (match_type == IPE_MATCH_RULE)
+		audit_rule(ab, r);
+	else if (match_type == IPE_MATCH_TABLE)
+		audit_log_format(ab, "rule=\"DEFAULT op=%s action=%s\"", op,
+				 ACTSTR(act));
+	else
+		audit_log_format(ab, "rule=\"DEFAULT action=%s\"",
+				 ACTSTR(act));
+
+	audit_log_end(ab);
+}

--
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