[PATCH v31 25/28] Audit: Add record for multiple task security contexts

[Casey Schaufler]

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 at schaufler-ca.com>
---
 include/linux/security.h   |  9 ++++++
 include/uapi/linux/audit.h |  1 +
 kernel/audit.c             | 58 ++++++++++++++++++++++++++++++++------
 3 files changed, 60 insertions(+), 8 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index bec8505f2ce5..a54179451410 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -231,6 +231,15 @@ static inline bool lsmblob_equal(struct lsmblob *bloba, struct lsmblob *blobb)
 extern int lsm_name_to_slot(char *name);
 extern const char *lsm_slot_to_name(int slot);
 
+static inline bool lsm_multiple_contexts(void)
+{
+#ifdef CONFIG_SECURITY
+	return lsm_slot_to_name(1) != NULL;
+#else
+	return false;
+#endif
+}
+
 /**
  * lsmblob_value - find the first non-zero value in an lsmblob structure.
  * @blob: Pointer to the data
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 9176a095fefc..86ad3da4f0d4 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 fc3662ff126e..4ee2bf620df7 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -197,6 +197,9 @@ static struct audit_ctl_mutex {
 struct audit_context_entry {
 	struct list_head	list;
 	int			type;	/* Audit record type */
+	union {
+		struct lsmblob	lsm_subjs;
+	};
 };
 
 /* The audit_buffer is used when formatting an audit record.  The caller
@@ -2149,15 +2152,30 @@ 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 {
+		struct audit_context_entry *ace;
+
+		audit_log_format(ab, " subj=?");
+		ace = kzalloc(sizeof(*ace), ab->gfp_mask);
+		if (!ace) {
+			error = -ENOMEM;
 			goto error_path;
-		return 0;
+		}
+		INIT_LIST_HEAD(&ace->list);
+		ace->type = AUDIT_MAC_TASK_CONTEXTS;
+		ace->lsm_subjs = blob;
+		list_add(&ace->list, &ab->aux_records);
 	}
-
-	audit_log_format(ab, " subj=%s", context.context);
-	security_release_secctx(&context);
 	return 0;
 
 error_path:
@@ -2419,9 +2437,12 @@ void audit_log_end(struct audit_buffer *ab)
 	struct audit_context_entry *entry;
 	struct audit_context mcontext;
 	struct audit_context *mctx;
+	struct lsmcontext lcontext;
 	struct audit_buffer *mab;
 	struct list_head *l;
 	struct list_head *n;
+	int rc;
+	int i;
 
 	if (!ab)
 		return;
@@ -2434,6 +2455,7 @@ void audit_log_end(struct audit_buffer *ab)
 	}
 
 	if (ab->ctx == NULL) {
+		mcontext.context = AUDIT_CTX_SYSCALL;
 		mcontext.stamp = ab->stamp;
 		mctx = &mcontext;
 	} else
@@ -2447,7 +2469,27 @@ void audit_log_end(struct audit_buffer *ab)
 			continue;
 		}
 		switch (entry->type) {
-		/* Don't know of any quite yet. */
+		case AUDIT_MAC_TASK_CONTEXTS:
+			for (i = 0; i < LSMBLOB_ENTRIES; i++) {
+				if (entry->lsm_subjs.secid[i] == 0)
+					continue;
+				rc = security_secid_to_secctx(&entry->lsm_subjs,
+							      &lcontext, i);
+				if (rc) {
+					if (rc != -EINVAL)
+						audit_panic("error in audit_log_end");
+					audit_log_format(mab, "%ssubj_%s=?",
+							 i ? " " : "",
+							 lsm_slot_to_name(i));
+				} else {
+					audit_log_format(mab, "%ssubj_%s=%s",
+							 i ? " " : "",
+							 lsm_slot_to_name(i),
+							 lcontext.context);
+					security_release_secctx(&lcontext);
+				}
+			}
+			break;
 		default:
 			audit_panic("Unknown type in audit_log_end");
 			break;
-- 
2.31.1