Merge tag 'blob-stacking-security-next' of https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux into next-general

LSM: Module stacking for SARA and Landlock

The combined series of LSM refactoring and addition of blob-sharing for
SARA and Landlock.

From Casey:

v5: Include Kees Cook's rework of the lsm command
    line interface.
v4: Finer granularity in the patches and other
    cleanups suggested by Kees Cook.
    Removed dead code created by the removal of SELinux
    credential blob poisoning.
v3: Add ipc blob for SARA and task blob for Landlock.
    Removing the SELinux cred blob pointer poisoning
    results selinux_is_enabled() being unused, so it and
    all it's overhead has been removed.
    Broke up the cred infrastructure patch.
v2: Reduce the patchset to what is required to support
    the proposed SARA and LandLock security modules

The SARA security module is intended to be used
in conjunction with other security modules. It requires
state to be maintained for the credential, which
in turn requires a mechanism for sharing the credential
security blob. It also uses the ipc security blob. The
module also requires mechanism for user space manipulation
of the credential information, hence an additional
subdirectory in /proc/.../attr.

The LandLock security module provides user configurable
policy in the secmark mechanism. It requires data in
the credential, file, inode and task security blobs. For
this to be used along side the existing "major" security
modules mechanism for sharing these blobs are provided.

A side effect of providing sharing of the crendential
security blob is that the TOMOYO module can be used at
the same time as the other "major" modules.

The mechanism for configuring which security modules are
enabled has to change when stacking in enabled. Any
module that uses just the security blobs that are shared
can be selected. Additionally, one other "major" module
can be selected.

The security module stacking issues around networking and
IPC are not addressed here as they are beyond what is
required for TOMOYO, SARA and LandLock.

1 files changed, 31 insertions, 34 deletions

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 2c010874329f..60ef71268ccf 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -60,7 +60,7 @@ DEFINE_PER_CPU(struct aa_buffers, aa_buffers);
 static void apparmor_cred_free(struct cred *cred)
 {
 	aa_put_label(cred_label(cred));
-	cred_label(cred) = NULL;
+	set_cred_label(cred, NULL);
 }
 
 /*
@@ -68,7 +68,7 @@ static void apparmor_cred_free(struct cred *cred)
  */
 static int apparmor_cred_alloc_blank(struct cred *cred, gfp_t gfp)
 {
-	cred_label(cred) = NULL;
+	set_cred_label(cred, NULL);
 	return 0;
 }
 
@@ -78,7 +78,7 @@ static int apparmor_cred_alloc_blank(struct cred *cred, gfp_t gfp)
 static int apparmor_cred_prepare(struct cred *new, const struct cred *old,
 				 gfp_t gfp)
 {
-	cred_label(new) = aa_get_newest_label(cred_label(old));
+	set_cred_label(new, aa_get_newest_label(cred_label(old)));
 	return 0;
 }
 
@@ -87,26 +87,21 @@ static int apparmor_cred_prepare(struct cred *new, const struct cred *old,
  */
 static void apparmor_cred_transfer(struct cred *new, const struct cred *old)
 {
-	cred_label(new) = aa_get_newest_label(cred_label(old));
+	set_cred_label(new, aa_get_newest_label(cred_label(old)));
 }
 
 static void apparmor_task_free(struct task_struct *task)
 {
 
 	aa_free_task_ctx(task_ctx(task));
-	task_ctx(task) = NULL;
 }
 
 static int apparmor_task_alloc(struct task_struct *task,
 			       unsigned long clone_flags)
 {
-	struct aa_task_ctx *new = aa_alloc_task_ctx(GFP_KERNEL);
-
-	if (!new)
-		return -ENOMEM;
+	struct aa_task_ctx *new = task_ctx(task);
 
 	aa_dup_task_ctx(new, task_ctx(current));
-	task_ctx(task) = new;
 
 	return 0;
 }
@@ -434,21 +429,21 @@ static int apparmor_file_open(struct file *file)
 
 static int apparmor_file_alloc_security(struct file *file)
 {
-	int error = 0;
-
-	/* freed by apparmor_file_free_security */
+	struct aa_file_ctx *ctx = file_ctx(file);
 	struct aa_label *label = begin_current_label_crit_section();
-	file->f_security = aa_alloc_file_ctx(label, GFP_KERNEL);
-	if (!file_ctx(file))
-		error = -ENOMEM;
-	end_current_label_crit_section(label);
 
-	return error;
+	spin_lock_init(&ctx->lock);
+	rcu_assign_pointer(ctx->label, aa_get_label(label));
+	end_current_label_crit_section(label);
+	return 0;
 }
 
 static void apparmor_file_free_security(struct file *file)
 {
-	aa_free_file_ctx(file_ctx(file));
+	struct aa_file_ctx *ctx = file_ctx(file);
+
+	if (ctx)
+		aa_put_label(rcu_access_pointer(ctx->label));
 }
 
 static int common_file_perm(const char *op, struct file *file, u32 mask)
@@ -1151,6 +1146,15 @@ static int apparmor_inet_conn_request(struct sock *sk, struct sk_buff *skb,
 }
 #endif
 
+/*
+ * The cred blob is a pointer to, not an instance of, an aa_task_ctx.
+ */
+struct lsm_blob_sizes apparmor_blob_sizes __lsm_ro_after_init = {
+	.lbs_cred = sizeof(struct aa_task_ctx *),
+	.lbs_file = sizeof(struct aa_file_ctx),
+	.lbs_task = sizeof(struct aa_task_ctx),
+};
+
 static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(ptrace_access_check, apparmor_ptrace_access_check),
 	LSM_HOOK_INIT(ptrace_traceme, apparmor_ptrace_traceme),
@@ -1333,8 +1337,8 @@ bool aa_g_paranoid_load = true;
 module_param_named(paranoid_load, aa_g_paranoid_load, aabool, S_IRUGO);
 
 /* Boot time disable flag */
-static bool apparmor_enabled = CONFIG_SECURITY_APPARMOR_BOOTPARAM_VALUE;
-module_param_named(enabled, apparmor_enabled, bool, S_IRUGO);
+static int apparmor_enabled __lsm_ro_after_init = 1;
+module_param_named(enabled, apparmor_enabled, int, 0444);
 
 static int __init apparmor_enabled_setup(char *str)
 {
@@ -1479,14 +1483,10 @@ static int param_set_mode(const char *val, const struct kernel_param *kp)
 static int __init set_init_ctx(void)
 {
 	struct cred *cred = (struct cred *)current->real_cred;
-	struct aa_task_ctx *ctx;
-
-	ctx = aa_alloc_task_ctx(GFP_KERNEL);
-	if (!ctx)
-		return -ENOMEM;
 
-	cred_label(cred) = aa_get_label(ns_unconfined(root_ns));
-	task_ctx(current) = ctx;
+	lsm_early_cred(cred);
+	lsm_early_task(current);
+	set_cred_label(cred, aa_get_label(ns_unconfined(root_ns)));
 
 	return 0;
 }
@@ -1663,12 +1663,6 @@ static int __init apparmor_init(void)
 {
 	int error;
 
-	if (!apparmor_enabled || !security_module_enable("apparmor")) {
-		aa_info_message("AppArmor disabled by boot time parameter");
-		apparmor_enabled = false;
-		return 0;
-	}
-
 	aa_secids_init();
 
 	error = aa_setup_dfa_engine();
@@ -1729,5 +1723,8 @@ alloc_out:
 
 DEFINE_LSM(apparmor) = {
 	.name = "apparmor",
+	.flags = LSM_FLAG_LEGACY_MAJOR | LSM_FLAG_EXCLUSIVE,
+	.enabled = &apparmor_enabled,
+	.blobs = &apparmor_blob_sizes,
 	.init = apparmor_init,
 };