Audit: Add record for multiple process LSM attributes

Create a new audit record type to contain the subject information
when there are multiple security modules that require such data.
This record is linked with the same timestamp and serial number
using the audit_alloc_local() mechanism.
The record is produced only in cases where there is more than one
security module with a process "context".
In cases where this record is produced the subj= fields of
other records in the audit event will be set to "subj=?".

An example of the MAC_TASK_CONTEXTS (1420) record is:

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

There will be a subj_$LSM= entry for each security module
LSM that supports the secid_to_secctx and secctx_to_secid
hooks. The BPF security module implements secid/secctx
translation hooks, so it has to be considered to provide a
secctx even though it may not actually do so.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
To: paul@paul-moore.com
To: linux-audit@redhat.com
To: rgb@redhat.com
Cc: netdev@vger.kernel.org

drivers/android/binder.c

@@ -2722,7 +2722,7 @@ static void binder_transaction(struct binder_proc *proc,
 		 * case well anyway.
 		 */
 		security_task_getsecid_obj(proc->tsk, &blob);
-		ret = security_secid_to_secctx(&blob, &lsmctx);
+		ret = security_secid_to_secctx(&blob, &lsmctx, LSMBLOB_DISPLAY);
 		if (ret) {
 			return_error = BR_FAILED_REPLY;
 			return_error_param = ret;

include/linux/audit.h

@@ -291,6 +291,7 @@ extern int  audit_alloc(struct task_struct *task);
 extern void __audit_free(struct task_struct *task);
 extern struct audit_context *audit_alloc_local(gfp_t gfpflags);
 extern void audit_free_context(struct audit_context *context);
+extern void audit_free_local(struct audit_context *context);
 extern void __audit_syscall_entry(int major, unsigned long a0, unsigned long a1,
 				  unsigned long a2, unsigned long a3);
 extern void __audit_syscall_exit(int ret_success, long ret_value);
@@ -386,6 +387,19 @@ static inline void audit_ptrace(struct task_struct *t)
 		__audit_ptrace(t);
 }
 
+static inline struct audit_context *audit_alloc_for_lsm(gfp_t gfp)
+{
+	struct audit_context *context = audit_context();
+
+	if (context)
+		return context;
+
+	if (lsm_multiple_contexts())
+		return audit_alloc_local(gfp);
+
+	return NULL;
+}
+
 				/* Private API (for audit.c only) */
 extern void __audit_ipc_obj(struct kern_ipc_perm *ipcp);
 extern void __audit_ipc_set_perm(unsigned long qbytes, uid_t uid, gid_t gid, umode_t mode);
@@ -560,6 +574,8 @@ extern int audit_signals;
 }
 static inline void audit_free_context(struct audit_context *context)
 { }
+static inline void audit_free_local(struct audit_context *context)
+{ }
 static inline int audit_alloc(struct task_struct *task)
 {
 	return 0;

include/linux/security.h

@@ -182,6 +182,8 @@ struct lsmblob {
 #define LSMBLOB_INVALID		-1	/* Not a valid LSM slot number */
 #define LSMBLOB_NEEDED		-2	/* Slot requested on initialization */
 #define LSMBLOB_NOT_NEEDED	-3	/* Slot not requested */
+#define LSMBLOB_DISPLAY		-4	/* Use the "display" slot */
+#define LSMBLOB_FIRST		-5	/* Use the default "display" slot */
 
 /**
  * lsmblob_init - initialize an lsmblob structure
@@ -248,6 +250,15 @@ static inline u32 lsmblob_value(const struct lsmblob *blob)
 	return 0;
 }
 
+static inline bool lsm_multiple_contexts(void)
+{
+#ifdef CONFIG_SECURITY
+	return lsm_slot_to_name(1) != NULL;
+#else
+	return false;
+#endif
+}
+
 /* These functions are in security/commoncap.c */
 extern int cap_capable(const struct cred *cred, struct user_namespace *ns,
 		       int cap, unsigned int opts);
@@ -578,7 +589,8 @@ int security_setprocattr(const char *lsm, const char *name, void *value,
 			 size_t size);
 int security_netlink_send(struct sock *sk, struct sk_buff *skb);
 int security_ismaclabel(const char *name);
-int security_secid_to_secctx(struct lsmblob *blob, struct lsmcontext *cp);
+int security_secid_to_secctx(struct lsmblob *blob, struct lsmcontext *cp,
+			     int display);
 int security_secctx_to_secid(const char *secdata, u32 seclen,
 			     struct lsmblob *blob);
 void security_release_secctx(struct lsmcontext *cp);
@@ -1433,7 +1445,7 @@ static inline int security_ismaclabel(const char *name)
 }
 
 static inline int security_secid_to_secctx(struct lsmblob *blob,
-					   struct lsmcontext *cp)
+					   struct lsmcontext *cp, int display)
 {
 	return -EOPNOTSUPP;
 }

include/net/netlabel.h

@@ -97,7 +97,7 @@ struct calipso_doi;
 
 /* NetLabel audit information */
 struct netlbl_audit {
-	u32 secid;
+	struct lsmblob lsmdata;
 	kuid_t loginuid;
 	unsigned int sessionid;
 };

include/net/scm.h

@@ -101,7 +101,7 @@ static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct sc
 		 * and the infrastructure will know which it is.
 		 */
 		lsmblob_init(&lb, scm->secid);
-		err = security_secid_to_secctx(&lb, &context);
+		err = security_secid_to_secctx(&lb, &context, LSMBLOB_DISPLAY);
 
 		if (!err) {
 			put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, context.len,

include/net/xfrm.h

@@ -669,13 +669,22 @@ struct xfrm_spi_skb_cb {
 #define XFRM_SPI_SKB_CB(__skb) ((struct xfrm_spi_skb_cb *)&((__skb)->cb[0]))
 
 #ifdef CONFIG_AUDITSYSCALL
-static inline struct audit_buffer *xfrm_audit_start(const char *op)
+static inline struct audit_buffer *xfrm_audit_start(const char *op,
+						    struct audit_context **lac)
 {
+	struct audit_context *context;
 	struct audit_buffer *audit_buf = NULL;
 
 	if (audit_enabled == AUDIT_OFF)
 		return NULL;
-	audit_buf = audit_log_start(audit_context(), GFP_ATOMIC,
+	context = audit_context();
+	if (lac != NULL) {
+		if (lsm_multiple_contexts() && context == NULL)
+			context = audit_alloc_local(GFP_ATOMIC);
+		*lac = context;
+	}
+
+	audit_buf = audit_log_start(context, GFP_ATOMIC,
 				    AUDIT_MAC_IPSEC_EVENT);
 	if (audit_buf == NULL)
 		return NULL;

include/uapi/linux/audit.h

@@ -139,6 +139,7 @@
 #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 contexts */
 
 #define AUDIT_FIRST_KERN_ANOM_MSG   1700
 #define AUDIT_LAST_KERN_ANOM_MSG    1799

kernel/audit.c

@@ -386,10 +386,12 @@ void audit_log_lost(const char *message)
 static int audit_log_config_change(char *function_name, u32 new, u32 old,
 				   int allow_changes)
 {
+	struct audit_context *context;
 	struct audit_buffer *ab;
 	int rc = 0;
 
-	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_CONFIG_CHANGE);
+	context = audit_alloc_for_lsm(GFP_KERNEL);
+	ab = audit_log_start(context, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
 	if (unlikely(!ab))
 		return rc;
 	audit_log_format(ab, "op=set %s=%u old=%u ", function_name, new, old);
@@ -399,6 +401,7 @@ static int audit_log_config_change(char *function_name, u32 new, u32 old,
 		allow_changes = 0; /* Something weird, deny request */
 	audit_log_format(ab, " res=%d", allow_changes);
 	audit_log_end(ab);
+	audit_free_local(context);
 	return rc;
 }
 
@@ -1072,12 +1075,6 @@ static void audit_log_common_recv_msg(struct audit_context *context,
 	audit_log_task_context(*ab);
 }
 
-static inline void audit_log_user_recv_msg(struct audit_buffer **ab,
-					   u16 msg_type)
-{
-	audit_log_common_recv_msg(NULL, ab, msg_type);
-}
-
 int is_audit_feature_set(int i)
 {
 	return af.features & AUDIT_FEATURE_TO_MASK(i);
@@ -1190,6 +1187,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 	struct audit_buffer	*ab;
 	u16			msg_type = nlh->nlmsg_type;
 	struct audit_sig_info   *sig_data;
+	struct audit_context	*lcontext;
 
 	err = audit_netlink_ok(skb, msg_type);
 	if (err)
@@ -1357,7 +1355,8 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 				if (err)
 					break;
 			}
-			audit_log_user_recv_msg(&ab, msg_type);
+			lcontext = audit_alloc_for_lsm(GFP_KERNEL);
+			audit_log_common_recv_msg(lcontext, &ab, msg_type);
 			if (msg_type != AUDIT_USER_TTY) {
 				/* ensure NULL termination */
 				str[data_len - 1] = '\0';
@@ -1371,20 +1370,23 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 				audit_log_n_untrustedstring(ab, str, data_len);
 			}
 			audit_log_end(ab);
+			audit_free_local(lcontext);
 		}
 		break;
 	case AUDIT_ADD_RULE:
 	case AUDIT_DEL_RULE:
 		if (data_len < sizeof(struct audit_rule_data))
 			return -EINVAL;
 		if (audit_enabled == AUDIT_LOCKED) {
-			audit_log_common_recv_msg(audit_context(), &ab,
+			lcontext = audit_alloc_for_lsm(GFP_KERNEL);
+			audit_log_common_recv_msg(lcontext, &ab,
 						  AUDIT_CONFIG_CHANGE);
 			audit_log_format(ab, " op=%s audit_enabled=%d res=0",
 					 msg_type == AUDIT_ADD_RULE ?
 						"add_rule" : "remove_rule",
 					 audit_enabled);
 			audit_log_end(ab);
+			audit_free_local(lcontext);
 			return -EPERM;
 		}
 		err = audit_rule_change(msg_type, seq, data, data_len);
@@ -1394,10 +1396,11 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		break;
 	case AUDIT_TRIM:
 		audit_trim_trees();
-		audit_log_common_recv_msg(audit_context(), &ab,
-					  AUDIT_CONFIG_CHANGE);
+		lcontext = audit_alloc_for_lsm(GFP_KERNEL);
+		audit_log_common_recv_msg(lcontext, &ab, AUDIT_CONFIG_CHANGE);
 		audit_log_format(ab, " op=trim res=1");
 		audit_log_end(ab);
+		audit_free_local(lcontext);
 		break;
 	case AUDIT_MAKE_EQUIV: {
 		void *bufp = data;
@@ -1425,14 +1428,15 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		/* OK, here comes... */
 		err = audit_tag_tree(old, new);
 
-		audit_log_common_recv_msg(audit_context(), &ab,
-					  AUDIT_CONFIG_CHANGE);
+		lcontext = audit_alloc_for_lsm(GFP_KERNEL);
+		audit_log_common_recv_msg(lcontext, &ab, AUDIT_CONFIG_CHANGE);
 		audit_log_format(ab, " op=make_equiv old=");
 		audit_log_untrustedstring(ab, old);
 		audit_log_format(ab, " new=");
 		audit_log_untrustedstring(ab, new);
 		audit_log_format(ab, " res=%d", !err);
 		audit_log_end(ab);
+		audit_free_local(lcontext);
 		kfree(old);
 		kfree(new);
 		break;
@@ -1443,7 +1447,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 
 		if (lsmblob_is_set(&audit_sig_lsm)) {
 			err = security_secid_to_secctx(&audit_sig_lsm,
-						       &context);
+						       &context, LSMBLOB_FIRST);
 			if (err)
 				return err;
 		}
@@ -1498,13 +1502,14 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		old.enabled = t & AUDIT_TTY_ENABLE;
 		old.log_passwd = !!(t & AUDIT_TTY_LOG_PASSWD);
 
-		audit_log_common_recv_msg(audit_context(), &ab,
-					  AUDIT_CONFIG_CHANGE);
+		lcontext = audit_alloc_for_lsm(GFP_KERNEL);
+		audit_log_common_recv_msg(lcontext, &ab, AUDIT_CONFIG_CHANGE);
 		audit_log_format(ab, " op=tty_set old-enabled=%d new-enabled=%d"
 				 " old-log_passwd=%d new-log_passwd=%d res=%d",
 				 old.enabled, s.enabled, old.log_passwd,
 				 s.log_passwd, !err);
 		audit_log_end(ab);
+		audit_free_local(lcontext);
 		break;
 	}
 	default:
@@ -1550,6 +1555,7 @@ static void audit_receive(struct sk_buff  *skb)
 /* Log information about who is connecting to the audit multicast socket */
 static void audit_log_multicast(int group, const char *op, int err)
 {
+	struct audit_context *context;
 	const struct cred *cred;
 	struct tty_struct *tty;
 	char comm[sizeof(current->comm)];
@@ -1558,7 +1564,8 @@ static void audit_log_multicast(int group, const char *op, int err)
 	if (!audit_enabled)
 		return;
 
-	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_EVENT_LISTENER);
+	context = audit_alloc_for_lsm(GFP_KERNEL);
+	ab = audit_log_start(context, GFP_KERNEL, AUDIT_EVENT_LISTENER);
 	if (!ab)
 		return;
 
@@ -1577,6 +1584,7 @@ static void audit_log_multicast(int group, const char *op, int err)
 	audit_log_d_path_exe(ab, current->mm); /* exe= */
 	audit_log_format(ab, " nl-mcgrp=%d op=%s res=%d", group, op, !err);
 	audit_log_end(ab);
+	audit_free_local(context);
 }
 
 /* Run custom bind function on netlink socket group connect or bind requests. */
@@ -2128,6 +2136,36 @@ void audit_log_key(struct audit_buffer *ab, char *key)
 		audit_log_format(ab, "(null)");
 }
 
+static void audit_log_lsm(struct audit_context *context, struct lsmblob *blob)
+{
+	struct audit_buffer *ab;
+	struct lsmcontext lsmdata;
+	bool sep = false;
+	int error;
+	int i;
+
+	ab = audit_log_start(context, GFP_ATOMIC, AUDIT_MAC_TASK_CONTEXTS);
+	if (!ab)
+		return; /* audit_panic or being filtered */
+
+	for (i = 0; i < LSMBLOB_ENTRIES; i++) {
+		if (blob->secid[i] == 0)
+			continue;
+		error = security_secid_to_secctx(blob, &lsmdata, i);
+		if (error && error != -EINVAL) {
+			audit_panic("error in audit_log_lsm");
+			return;
+		}
+
+		audit_log_format(ab, "%ssubj_%s=%s", sep ? " " : "",
+				 lsm_slot_to_name(i), lsmdata.context);
+		sep = true;
+
+		security_release_secctx(&lsmdata);
+	}
+	audit_log_end(ab);
+}
+
 int audit_log_task_context(struct audit_buffer *ab)
 {
 	int error;
@@ -2138,7 +2176,18 @@ int audit_log_task_context(struct audit_buffer *ab)
 	if (!lsmblob_is_set(&blob))
 		return 0;
 
-	error = security_secid_to_secctx(&blob, &context);
+	/*
+	 * If there is more than one security module that has a
+	 * subject "context" it's necessary to put the subject data
+	 * into a separate record to maintain compatibility.
+	 */
+	if (lsm_multiple_contexts()) {
+		audit_log_format(ab, " subj=?");
+		audit_log_lsm(ab->ctx, &blob);
+		return 0;
+	}
+
+	error = security_secid_to_secctx(&blob, &context, LSMBLOB_FIRST);
 	if (error) {
 		if (error != -EINVAL)
 			goto error_path;
@@ -2274,14 +2323,16 @@ static void audit_log_set_loginuid(kuid_t koldloginuid, kuid_t kloginuid,
 				   unsigned int oldsessionid,
 				   unsigned int sessionid, int rc)
 {
+	struct audit_context *context;
 	struct audit_buffer *ab;
 	uid_t uid, oldloginuid, loginuid;
 	struct tty_struct *tty;
 
 	if (!audit_enabled)
 		return;
 
-	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_LOGIN);
+	context = audit_alloc_for_lsm(GFP_KERNEL);
+	ab = audit_log_start(context, GFP_KERNEL, AUDIT_LOGIN);
 	if (!ab)
 		return;
 
@@ -2297,6 +2348,7 @@ static void audit_log_set_loginuid(kuid_t koldloginuid, kuid_t kloginuid,
 			 oldsessionid, sessionid, !rc);
 	audit_put_tty(tty);
 	audit_log_end(ab);
+	audit_free_local(context);
 }
 
 /**