[PATCH v31 26/28] Audit: Add record for multiple object security contexts

[Casey Schaufler <casey@schaufler-ca.com>]

Create a new audit record AUDIT_MAC_OBJ_CONTEXTS.
An example of the MAC_OBJ_CONTEXTS (1421) record is:

    type=MAC_OBJ_CONTEXTS[1421]
    msg=audit(1601152467.009:1050):
    obj_selinux=unconfined_u:object_r:user_home_t:s0

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

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 include/linux/audit.h      |  5 ++++
 include/uapi/linux/audit.h |  1 +
 kernel/audit.c             | 59 ++++++++++++++++++++++++++++++++++++++
 kernel/auditsc.c           | 37 ++++--------------------
 4 files changed, 70 insertions(+), 32 deletions(-)

diff --git a/include/linux/audit.h b/include/linux/audit.h
index 14849d5f84b4..94c87ec043c7 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -192,6 +192,8 @@ extern void		    audit_log_path_denied(int type,
 extern void		    audit_log_lost(const char *message);
 
 extern int audit_log_task_context(struct audit_buffer *ab);
+extern void audit_log_object_context(struct audit_buffer *ab,
+				     struct lsmblob *blob);
 extern void audit_log_task_info(struct audit_buffer *ab);
 
 extern int		    audit_update_lsm_rules(void);
@@ -255,6 +257,9 @@ static inline int audit_log_task_context(struct audit_buffer *ab)
 {
 	return 0;
 }
+static inline void audit_log_object_context(struct audit_buffer *ab,
+					    struct lsmblob *blob);
+{ }
 static inline void audit_log_task_info(struct audit_buffer *ab)
 { }
 
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 86ad3da4f0d4..116566d0fc03 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -144,6 +144,7 @@
 #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_MAC_OBJ_CONTEXTS	1421	/* Multiple LSM objext 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 4ee2bf620df7..85f278c21d4d 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -199,6 +199,7 @@ struct audit_context_entry {
 	int			type;	/* Audit record type */
 	union {
 		struct lsmblob	lsm_subjs;
+		struct lsmblob	lsm_objs;
 	};
 };
 
@@ -2184,6 +2185,43 @@ int audit_log_task_context(struct audit_buffer *ab)
 }
 EXPORT_SYMBOL(audit_log_task_context);
 
+void audit_log_object_context(struct audit_buffer *ab, struct lsmblob *blob)
+{
+	struct audit_context_entry *ace;
+	struct lsmcontext context;
+	int error;
+
+	if (!lsm_multiple_contexts()) {
+		error = security_secid_to_secctx(blob, &context, LSMBLOB_FIRST);
+		if (error) {
+			if (error != -EINVAL)
+				goto error_path;
+			return;
+		}
+		audit_log_format(ab, " obj=%s", context.context);
+		security_release_secctx(&context);
+	} else {
+		/*
+		 * If there is more than one security module that has a
+		 * object "context" it's necessary to put the object data
+		 * into a separate record to maintain compatibility.
+		 */
+		audit_log_format(ab, " obj=?");
+		ace = kzalloc(sizeof(*ace), ab->gfp_mask);
+		if (!ace)
+			goto error_path;
+		INIT_LIST_HEAD(&ace->list);
+		ace->type = AUDIT_MAC_OBJ_CONTEXTS;
+		ace->lsm_objs = *blob;
+		list_add(&ace->list, &ab->aux_records);
+	}
+	return;
+
+error_path:
+	audit_panic("error in audit_log_object_context");
+}
+EXPORT_SYMBOL(audit_log_object_context);
+
 void audit_log_d_path_exe(struct audit_buffer *ab,
 			  struct mm_struct *mm)
 {
@@ -2490,6 +2528,27 @@ void audit_log_end(struct audit_buffer *ab)
 				}
 			}
 			break;
+		case AUDIT_MAC_OBJ_CONTEXTS:
+			for (i = 0; i < LSMBLOB_ENTRIES; i++) {
+				if (entry->lsm_objs.secid[i] == 0)
+					continue;
+				rc = security_secid_to_secctx(&entry->lsm_objs,
+							      &lcontext, i);
+				if (rc) {
+					if (rc != -EINVAL)
+						audit_panic("error in audit_log_end");
+					audit_log_format(mab, "%sobj_%s=?",
+							 i ? " " : "",
+							 lsm_slot_to_name(i));
+				} else {
+					audit_log_format(mab, "%sobj_%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;
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 68a582fa87e6..60b77e37ae83 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1111,7 +1111,6 @@ static int audit_log_pid_context(struct audit_context *context, pid_t pid,
 				 struct lsmblob *blob, char *comm)
 {
 	struct audit_buffer *ab;
-	struct lsmcontext lsmctx;
 	int rc = 0;
 
 	ab = audit_log_start(context, GFP_KERNEL, AUDIT_OBJ_PID);
@@ -1121,15 +1120,8 @@ static int audit_log_pid_context(struct audit_context *context, pid_t pid,
 	audit_log_format(ab, "opid=%d oauid=%d ouid=%d oses=%d", pid,
 			 from_kuid(&init_user_ns, auid),
 			 from_kuid(&init_user_ns, uid), sessionid);
-	if (lsmblob_is_set(blob)) {
-		if (security_secid_to_secctx(blob, &lsmctx, LSMBLOB_FIRST)) {
-			audit_log_format(ab, " obj=(none)");
-			rc = 1;
-		} else {
-			audit_log_format(ab, " obj=%s", lsmctx.context);
-			security_release_secctx(&lsmctx);
-		}
-	}
+	if (lsmblob_is_set(blob))
+		audit_log_object_context(ab, blob);
 	audit_log_format(ab, " ocomm=");
 	audit_log_untrustedstring(ab, comm);
 	audit_log_end(ab);
@@ -1364,18 +1356,10 @@ static void show_special(struct audit_context *context, int *call_panic)
 				 from_kgid(&init_user_ns, context->ipc.gid),
 				 context->ipc.mode);
 		if (osid) {
-			struct lsmcontext lsmcxt;
 			struct lsmblob blob;
 
 			lsmblob_init(&blob, osid);
-			if (security_secid_to_secctx(&blob, &lsmcxt,
-						     LSMBLOB_FIRST)) {
-				audit_log_format(ab, " osid=%u", osid);
-				*call_panic = 1;
-			} else {
-				audit_log_format(ab, " obj=%s", lsmcxt.context);
-				security_release_secctx(&lsmcxt);
-			}
+			audit_log_object_context(ab, &blob);
 		}
 		if (context->ipc.has_perm) {
 			audit_log_end(ab);
@@ -1527,19 +1511,8 @@ static void audit_log_name(struct audit_context *context, struct audit_names *n,
 				 from_kgid(&init_user_ns, n->gid),
 				 MAJOR(n->rdev),
 				 MINOR(n->rdev));
-	if (lsmblob_is_set(&n->lsmblob)) {
-		struct lsmcontext lsmctx;
-
-		if (security_secid_to_secctx(&n->lsmblob, &lsmctx,
-					     LSMBLOB_FIRST)) {
-			audit_log_format(ab, " osid=?");
-			if (call_panic)
-				*call_panic = 2;
-		} else {
-			audit_log_format(ab, " obj=%s", lsmctx.context);
-			security_release_secctx(&lsmctx);
-		}
-	}
+	if (lsmblob_is_set(&n->lsmblob))
+		audit_log_object_context(ab, &n->lsmblob);
 
 	/* log the audit_names record type */
 	switch (n->type) {
-- 
2.31.1