[PATCH v2 4/6] Audit: Add record for multiple task security contexts

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

Create a new audit record AUDIT_MAC_TASK_CONTEXTS.
An example of the MAC_TASK_CONTEXTS (1423) record is:

    type=MAC_TASK_CONTEXTS[1423]
    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@schaufler-ca.com>
---
 include/linux/lsm_hooks.h  |  1 +
 include/linux/security.h   |  1 +
 include/uapi/linux/audit.h |  1 +
 kernel/audit.c             | 45 ++++++++++++++++++++++++++++++++------
 security/apparmor/lsm.c    |  1 +
 security/bpf/hooks.c       |  1 +
 security/security.c        |  3 +++
 security/selinux/hooks.c   |  1 +
 security/smack/smack_lsm.c |  1 +
 9 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 090d1d3e19fe..e4d303ab1f20 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -81,6 +81,7 @@ struct lsm_static_calls_table {
 struct lsm_id {
 	const char *name;
 	u64 id;
+	bool subjctx;
 };
 
 /*
diff --git a/include/linux/security.h b/include/linux/security.h
index 540894695c4b..79a9bf4a7cdd 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -168,6 +168,7 @@ struct lsm_prop {
 
 extern const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1];
 extern u32 lsm_active_cnt;
+extern u32 lsm_subjctx_cnt;
 extern const struct lsm_id *lsm_idlist[];
 
 /* These functions are in security/commoncap.c */
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index d9a069b4a775..5ebb5d80363d 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -146,6 +146,7 @@
 #define AUDIT_IPE_ACCESS	1420	/* IPE denial or grant */
 #define AUDIT_IPE_CONFIG_CHANGE	1421	/* IPE config change */
 #define AUDIT_IPE_POLICY_LOAD	1422	/* IPE policy load */
+#define AUDIT_MAC_TASK_CONTEXTS	1423	/* 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 293364bba961..59eaf69ee8ac 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -54,6 +54,7 @@
 #include <net/netlink.h>
 #include <linux/skbuff.h>
 #include <linux/security.h>
+#include <linux/lsm_hooks.h>
 #include <linux/freezer.h>
 #include <linux/pid_namespace.h>
 #include <net/netns/generic.h>
@@ -2241,21 +2242,51 @@ int audit_log_task_context(struct audit_buffer *ab)
 {
 	struct lsm_prop prop;
 	struct lsm_context ctx;
+	bool space = false;
 	int error;
+	int i;
 
 	security_current_getlsmprop_subj(&prop);
 	if (!lsmprop_is_set(&prop))
 		return 0;
 
-	error = security_lsmprop_to_secctx(&prop, &ctx, LSM_ID_UNDEF);
-	if (error < 0) {
-		if (error != -EINVAL)
-			goto error_path;
+	if (lsm_subjctx_cnt < 2) {
+		error = security_lsmprop_to_secctx(&prop, &ctx, LSM_ID_UNDEF);
+		if (error < 0) {
+			if (error != -EINVAL)
+				goto error_path;
+			return 0;
+		}
+		audit_log_format(ab, " subj=%s", ctx.context);
+		security_release_secctx(&ctx);
 		return 0;
 	}
-
-	audit_log_format(ab, " subj=%s", ctx.context);
-	security_release_secctx(&ctx);
+	/* 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;
+
+	for (i = 0; i < lsm_active_cnt; i++) {
+		if (!lsm_idlist[i]->subjctx)
+			continue;
+		error = security_lsmprop_to_secctx(&prop, &ctx,
+						   lsm_idlist[i]->id);
+		if (error < 0) {
+			if (error == -EOPNOTSUPP)
+				continue;
+			audit_log_format(ab, "%ssubj_%s=?", space ? " " : "",
+					 lsm_idlist[i]->name);
+			if (error != -EINVAL)
+				audit_panic("error in audit_log_task_context");
+		} else {
+			audit_log_format(ab, "%ssubj_%s=%s", space ? " " : "",
+					 lsm_idlist[i]->name, ctx.context);
+			security_release_secctx(&ctx);
+		}
+		space = true;
+	}
+	audit_buffer_aux_end(ab);
 	return 0;
 
 error_path:
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 9b6c2f157f83..17ec93a8d3fc 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1427,6 +1427,7 @@ struct lsm_blob_sizes apparmor_blob_sizes __ro_after_init = {
 static const struct lsm_id apparmor_lsmid = {
 	.name = "apparmor",
 	.id = LSM_ID_APPARMOR,
+	.subjctx = true,
 };
 
 static struct security_hook_list apparmor_hooks[] __ro_after_init = {
diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
index db759025abe1..aaaa1227ce13 100644
--- a/security/bpf/hooks.c
+++ b/security/bpf/hooks.c
@@ -18,6 +18,7 @@ static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {
 static const struct lsm_id bpf_lsmid = {
 	.name = "bpf",
 	.id = LSM_ID_BPF,
+	.subjctx = false, /* property exists, but will not be used */
 };
 
 static int __init bpf_lsm_init(void)
diff --git a/security/security.c b/security/security.c
index 55f9c7ad3f89..8450cc5f82d5 100644
--- a/security/security.c
+++ b/security/security.c
@@ -320,6 +320,7 @@ static void __init initialize_lsm(struct lsm_info *lsm)
  * Current index to use while initializing the lsm id list.
  */
 u32 lsm_active_cnt __ro_after_init;
+u32 lsm_subjctx_cnt __ro_after_init;
 const struct lsm_id *lsm_idlist[MAX_LSM_COUNT];
 
 /* Populate ordered LSMs list from comma-separated LSM name list. */
@@ -626,6 +627,8 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count,
 		if (lsm_active_cnt >= MAX_LSM_COUNT)
 			panic("%s Too many LSMs registered.\n", __func__);
 		lsm_idlist[lsm_active_cnt++] = lsmid;
+		if (lsmid->subjctx)
+			lsm_subjctx_cnt++;
 	}
 
 	for (i = 0; i < count; i++) {
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 7b867dfec88b..1e2e1545eb2e 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -7142,6 +7142,7 @@ static int selinux_uring_cmd(struct io_uring_cmd *ioucmd)
 static const struct lsm_id selinux_lsmid = {
 	.name = "selinux",
 	.id = LSM_ID_SELINUX,
+	.subjctx = true,
 };
 
 /*
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 239773cdcdcf..75bd62fe1513 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -5057,6 +5057,7 @@ struct lsm_blob_sizes smack_blob_sizes __ro_after_init = {
 static const struct lsm_id smack_lsmid = {
 	.name = "smack",
 	.id = LSM_ID_SMACK,
+	.subjctx = true,
 };
 
 static struct security_hook_list smack_hooks[] __ro_after_init = {
-- 
2.47.0