audit: add record for multiple task security contexts

Replace the single skb pointer in an audit_buffer with a list of
skb pointers. Add the audit_stamp information to the audit_buffer as
there's no guarantee that there will be an audit_context containing
the stamp associated with the event. At audit_log_end() time create
auxiliary records as have been added to the list. Functions are
created to manage the skb list in the audit_buffer.

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

    type=MAC_TASK_CONTEXTS
      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.

Refactor audit_log_task_context(), creating a new audit_log_subj_ctx().
This is used in netlabel auditing to provide multiple subject security
contexts as necessary.

Suggested-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
[PM: subj tweak, audit example readability indents]
Signed-off-by: Paul Moore <paul@paul-moore.com>

2 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/audit.h b/include/linux/audit.h
index e3f06eba9c6e..a1f068bcb3a0 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -37,6 +37,8 @@ struct audit_watch;
 struct audit_tree;
 struct sk_buff;
 struct kern_ipc_perm;
+struct lsm_id;
+struct lsm_prop;
 
 struct audit_krule {
 	u32			pflags;
@@ -147,6 +149,9 @@ extern unsigned compat_signal_class[];
 #define AUDIT_TTY_ENABLE	BIT(0)
 #define AUDIT_TTY_LOG_PASSWD	BIT(1)
 
+/* bit values for audit_cfg_lsm */
+#define AUDIT_CFG_LSM_SECCTX_SUBJECT	BIT(0)
+
 struct filename;
 
 #define AUDIT_OFF	0
@@ -185,6 +190,7 @@ extern void		    audit_log_path_denied(int type,
 						  const char *operation);
 extern void		    audit_log_lost(const char *message);
 
+extern int audit_log_subj_ctx(struct audit_buffer *ab, struct lsm_prop *prop);
 extern int audit_log_task_context(struct audit_buffer *ab);
 extern void audit_log_task_info(struct audit_buffer *ab);
 
@@ -210,6 +216,8 @@ extern u32 audit_enabled;
 
 extern int audit_signal_info(int sig, struct task_struct *t);
 
+extern void audit_cfg_lsm(const struct lsm_id *lsmid, int flags);
+
 #else /* CONFIG_AUDIT */
 static inline __printf(4, 5)
 void audit_log(struct audit_context *ctx, gfp_t gfp_mask, int type,
@@ -245,6 +253,11 @@ static inline void audit_log_key(struct audit_buffer *ab, char *key)
 { }
 static inline void audit_log_path_denied(int type, const char *operation)
 { }
+static inline int audit_log_subj_ctx(struct audit_buffer *ab,
+				     struct lsm_prop *prop)
+{
+	return 0;
+}
 static inline int audit_log_task_context(struct audit_buffer *ab)
 {
 	return 0;
@@ -269,6 +282,9 @@ static inline int audit_signal_info(int sig, struct task_struct *t)
 	return 0;
 }
 
+static inline void audit_cfg_lsm(const struct lsm_id *lsmid, int flags)
+{ }
+
 #endif /* CONFIG_AUDIT */
 
 #ifdef CONFIG_AUDIT_COMPAT_GENERIC
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 9a4ecc9f6dc5..8cad2f307719 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -148,6 +148,7 @@
 #define AUDIT_IPE_POLICY_LOAD	1422	/* IPE policy load */
 #define AUDIT_LANDLOCK_ACCESS	1423	/* Landlock denial */
 #define AUDIT_LANDLOCK_DOMAIN	1424	/* Landlock domain status */
+#define AUDIT_MAC_TASK_CONTEXTS	1425	/* Multiple LSM task contexts */
 
 #define AUDIT_FIRST_KERN_ANOM_MSG   1700
 #define AUDIT_LAST_KERN_ANOM_MSG    1799