[PATCH v39 24/42] 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.

Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
---
 include/linux/lsm_hooks.h  |  2 ++
 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, 49 insertions(+), 7 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index efd4a0655159..605aaf38c3f5 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -47,12 +47,14 @@ struct security_hook_heads {
  * struct lsm_id - Identify a Linux Security Module.
  * @lsm: name of the LSM, must be approved by the LSM maintainers
  * @id: LSM ID number from uapi/linux/lsm.h
+ * @lsmblob: indicates the LSM has an entry in struct lsmblob
  *
  * Contains the information that identifies the LSM.
  */
 struct lsm_id {
 	const char	*name;
 	u64		id;
+	bool		lsmblob;
 };
 
 /*
diff --git a/include/linux/security.h b/include/linux/security.h
index 360a454d5f8e..947cb3a35db4 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -192,6 +192,7 @@ struct lsmblob {
 
 extern const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1];
 extern u32 lsm_active_cnt;
+extern u32 lsm_blob_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 d676ed2b246e..dc045164b86b 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 b194494c4dc4..9d971fa96c0e 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>
@@ -2228,21 +2229,51 @@ int audit_log_task_context(struct audit_buffer *ab)
 {
 	struct lsmcontext ctx;
 	struct lsmblob blob;
+	bool space = false;
 	int error;
+	int i;
 
 	security_current_getlsmblob_subj(&blob);
 	if (!lsmblob_is_set(&blob))
 		return 0;
 
-	error = security_lsmblob_to_secctx(&blob, &ctx, LSM_ID_UNDEF);
-	if (error < 0) {
-		if (error != -EINVAL)
-			goto error_path;
+	if (lsm_blob_cnt < 2) {
+		error = security_lsmblob_to_secctx(&blob, &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]->lsmblob)
+			continue;
+		error = security_lsmblob_to_secctx(&blob, &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 b5f3beb26d5a..075942b253ae 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1447,6 +1447,7 @@ struct lsm_blob_sizes apparmor_blob_sizes __ro_after_init = {
 static const struct lsm_id apparmor_lsmid = {
 	.name = "apparmor",
 	.id = LSM_ID_APPARMOR,
+	.lsmblob = true,
 };
 
 static struct security_hook_list apparmor_hooks[] __ro_after_init = {
diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
index 57b9ffd53c98..2da40774dd20 100644
--- a/security/bpf/hooks.c
+++ b/security/bpf/hooks.c
@@ -19,6 +19,7 @@ static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {
 static const struct lsm_id bpf_lsmid = {
 	.name = "bpf",
 	.id = LSM_ID_BPF,
+	.lsmblob = true,
 };
 
 static int __init bpf_lsm_init(void)
diff --git a/security/security.c b/security/security.c
index 444051575793..8ff6cef26e6c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -269,6 +269,7 @@ 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_blob_cnt __ro_after_init;
 const struct lsm_id *lsm_idlist[LSM_CONFIG_COUNT];
 
 /**
@@ -599,6 +600,8 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count,
 		if (lsm_active_cnt >= LSM_CONFIG_COUNT)
 			panic("%s Too many LSMs registered.\n", __func__);
 		lsm_idlist[lsm_active_cnt++] = lsmid;
+		if (lsmid->lsmblob)
+			lsm_blob_cnt++;
 	}
 
 	for (i = 0; i < count; i++) {
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ed4237223959..656f25337334 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -7092,6 +7092,7 @@ static int selinux_uring_cmd(struct io_uring_cmd *ioucmd)
 static const struct lsm_id selinux_lsmid = {
 	.name = "selinux",
 	.id = LSM_ID_SELINUX,
+	.lsmblob = true,
 };
 
 /*
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index a58e2c14f120..a9ab31a40e36 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -5069,6 +5069,7 @@ struct lsm_blob_sizes smack_blob_sizes __ro_after_init = {
 static const struct lsm_id smack_lsmid = {
 	.name = "smack",
 	.id = LSM_ID_SMACK,
+	.lsmblob = true,
 };
 
 static struct security_hook_list smack_hooks[] __ro_after_init = {
-- 
2.41.0