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

Casey Schaufler
2025-03-07T18:39:00Z

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