[PATCH v36 27/33] Audit: Add record for multiple task security contexts

[Casey Schaufler <casey@xxxxxxxxxxxxxxxx>]

Create a new audit record AUDIT_MAC_TASK_CONTEXTS.
An example of the MAC_TASK_CONTEXTS (1420) record is:

    type=MAC_TASK_CONTEXTS[1420]
    msg=audit(1600880931.832:113)
    subj_apparmor=unconfined
    subj_smack=_

When an audit event includes a AUDIT_MAC_TASK_CONTEXTS record
the "subj=" field in other records in the event will be "subj=?".
An AUDIT_MAC_TASK_CONTEXTS record is supplied when the system has
multiple security modules that may make access decisions based
on a subject security context.

Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
---
 include/uapi/linux/audit.h |  1 +
 kernel/audit.c             | 42 +++++++++++++++++++++++++++++++-------
 2 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 7c1dc818b1d5..7a5966b46f38 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -143,6 +143,7 @@
 #define AUDIT_MAC_UNLBL_STCDEL	1417	/* NetLabel: del a static label */
 #define AUDIT_MAC_CALIPSO_ADD	1418	/* NetLabel: add CALIPSO DOI entry */
 #define AUDIT_MAC_CALIPSO_DEL	1419	/* NetLabel: del CALIPSO DOI entry */
+#define AUDIT_MAC_TASK_CONTEXTS	1420	/* Multiple LSM task contexts */
 
 #define AUDIT_FIRST_KERN_ANOM_MSG   1700
 #define AUDIT_LAST_KERN_ANOM_MSG    1799
diff --git a/kernel/audit.c b/kernel/audit.c
index 987740374dfa..2333d7f59285 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -2228,6 +2228,7 @@ static void audit_buffer_aux_end(struct audit_buffer *ab)
 
 int audit_log_task_context(struct audit_buffer *ab)
 {
+	int i;
 	int error;
 	struct lsmblob blob;
 	struct lsmcontext context;
@@ -2236,16 +2237,43 @@ int audit_log_task_context(struct audit_buffer *ab)
 	if (!lsmblob_is_set(&blob))
 		return 0;
 
-	error = security_secid_to_secctx(&blob, &context, LSMBLOB_FIRST);
-
-	if (error) {
-		if (error != -EINVAL)
+	if (!lsm_multiple_contexts()) {
+		error = security_secid_to_secctx(&blob, &context,
+						 LSMBLOB_FIRST);
+		if (error) {
+			if (error != -EINVAL)
+				goto error_path;
+			return 0;
+		}
+		audit_log_format(ab, " subj=%s", context.context);
+		security_release_secctx(&context);
+	} else {
+		/* Multiple LSMs provide contexts. Include an aux record. */
+		audit_log_format(ab, " subj=?");
+		error = audit_buffer_aux_new(ab, AUDIT_MAC_TASK_CONTEXTS);
+		if (error)
 			goto error_path;
-		return 0;
+		for (i = 0; i < LSMBLOB_ENTRIES; i++) {
+			if (blob.secid[i] == 0)
+				continue;
+			error = security_secid_to_secctx(&blob, &context, i);
+			if (error) {
+				audit_log_format(ab, "%ssubj_%s=?",
+						 i ? " " : "",
+						 lsm_slot_to_name(i));
+				if (error != -EINVAL)
+					audit_panic("error in audit_log_task_context");
+			} else {
+				audit_log_format(ab, "%ssubj_%s=%s",
+						 i ? " " : "",
+						 lsm_slot_to_name(i),
+						 context.context);
+				security_release_secctx(&context);
+			}
+		}
+		audit_buffer_aux_end(ab);
 	}
 
-	audit_log_format(ab, " subj=%s", context.context);
-	security_release_secctx(&context);
 	return 0;
 
 error_path:
-- 
2.35.1