[PATCH 2/8] user_ns: 3 new hooks for LSM namespace operations

Lukasz Pawelczyk
2015-05-21T11:56:37Z

This commit implements 3 new LSM hooks that provide the means for LSMs
to embed their own security context within user namespace, effectively
creating some sort of a user_ns related security namespace.

The first one to take advantage of this mechanism is Smack.

The hooks has been documented in the in the security.h below.

Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@samsung.com>
---
include/linux/lsm_hooks.h | 28 ++++++++++++++++++++++++++++
include/linux/security.h | 23 +++++++++++++++++++++++
include/linux/user_namespace.h | 4 ++++
kernel/user.c | 3 +++
kernel/user_namespace.c | 18 ++++++++++++++++++
security/security.c | 28 ++++++++++++++++++++++++++++
6 files changed, 104 insertions(+)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index f014f25..b6e0c3d 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1260,6 +1260,23 @@
* audit_rule_init.
* @rule contains the allocated rule
*
+ * @userns_create:
+ * Allocates and fills the security part of a new user namespace.
+ * @ns points to a newly created user namespace.
+ * Returns 0 or an error code.
+ *
+ * @userns_free:
+ * Deallocates the security part of a user namespace.
+ * @ns points to a user namespace about to be destroyed.
+ *
+ * @userns_setns:
+ * Run during a setns syscall to add a process to an already existing
+ * user namespace. Returning failure here will block the operation
+ * requested from userspace (setns() with CLONE_NEWUSER).
+ * @nsproxy contains a nsproxy to which the user namespace will be assigned.
+ * @ns contains user namespace that is to be incorporated to the nsproxy.
+ * Returns 0 or an error code.
+ *
* @inode_notifysecctx:
* Notify the security module of what the security context of an inode
* should be. Initializes the incore security context managed by the
@@ -1611,6 +1628,12 @@ union security_list_options {
struct audit_context *actx);
void (*audit_rule_free)(void *lsmrule);
#endif /* CONFIG_AUDIT */
+
+#ifdef CONFIG_SECURITY
+ int (*userns_create)(struct user_namespace *ns);
+ void (*userns_free)(struct user_namespace *ns);
+ int (*userns_setns)(struct nsproxy *nsproxy, struct user_namespace *ns);
+#endif /* CONFIG_SECURITY */
};

struct security_hook_heads {
@@ -1822,6 +1845,11 @@ struct security_hook_heads {
struct list_head audit_rule_match;
struct list_head audit_rule_free;
#endif /* CONFIG_AUDIT */
+#ifdef CONFIG_SECURITY
+ struct list_head userns_create;
+ struct list_head userns_free;
+ struct list_head userns_setns;
+#endif /* CONFIG_SECURITY */
};

/*
diff --git a/include/linux/security.h b/include/linux/security.h
index 8c8175d..ec17ae1 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1583,6 +1583,29 @@ static inline void security_audit_rule_free(void *lsmrule)
#endif /* CONFIG_SECURITY */
#endif /* CONFIG_AUDIT */

+#ifdef CONFIG_SECURITY
+int security_userns_create(struct user_namespace *ns);
+void security_userns_free(struct user_namespace *ns);
+int security_userns_setns(struct nsproxy *nsproxy, struct user_namespace *ns);
+
+#else
+
+static inline int security_userns_create(struct user_namespace *ns)
+{
+ return 0;
+}
+
+static inline void security_userns_free(struct user_namespace *ns)
+{ }
+
+static inline int security_userns_setns(struct nsproxy *nsproxy,
+ struct user_namespace *ns)
+{
+ return 0;
+}
+
+#endif /* CONFIG_SECURITY */
+
#ifdef CONFIG_SECURITYFS

extern struct dentry *securityfs_create_file(const char *name, umode_t mode,
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 8297e5b..a9400cc 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -39,6 +39,10 @@ struct user_namespace {
struct key *persistent_keyring_register;
struct rw_semaphore persistent_keyring_register_sem;
#endif
+
+#ifdef CONFIG_SECURITY
+ void *security;
+#endif
};

extern struct user_namespace init_user_ns;
diff --git a/kernel/user.c b/kernel/user.c
index b069ccb..ce5419e 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -59,6 +59,9 @@ struct user_namespace init_user_ns = {
.persistent_keyring_register_sem =
__RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
#endif
+#ifdef CONFIG_SECURITY
+ .security = NULL,
+#endif
};
EXPORT_SYMBOL_GPL(init_user_ns);

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 4109f83..cadffb6 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -22,6 +22,7 @@
#include <linux/ctype.h>
#include <linux/projid.h>
#include <linux/fs_struct.h>
+#include <linux/security.h>

static struct kmem_cache *user_ns_cachep __read_mostly;
static DEFINE_MUTEX(userns_state_mutex);
@@ -108,6 +109,15 @@ int create_user_ns(struct cred *new)

set_cred_user_ns(new, ns);

+#ifdef CONFIG_SECURITY
+ ret = security_userns_create(ns);
+ if (ret) {
+ ns_free_inum(&ns->ns);
+ kmem_cache_free(user_ns_cachep, ns);
+ return ret;
+ }
+#endif
+
#ifdef CONFIG_PERSISTENT_KEYRINGS
init_rwsem(&ns->persistent_keyring_register_sem);
#endif
@@ -143,6 +153,9 @@ void free_user_ns(struct user_namespace *ns)
#ifdef CONFIG_PERSISTENT_KEYRINGS
key_put(ns->persistent_keyring_register);
#endif
+#ifdef CONFIG_SECURITY
+ security_userns_free(ns);
+#endif
ns_free_inum(&ns->ns);
kmem_cache_free(user_ns_cachep, ns);
ns = parent;
@@ -969,6 +982,7 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
{
struct user_namespace *user_ns = to_user_ns(ns);
struct cred *cred;
+ int err;

/* Don't allow gaining capabilities by reentering
* the same user namespace.
@@ -986,6 +1000,10 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return -EPERM;

+ err = security_userns_setns(nsproxy, user_ns);
+ if (err)
+ return err;
+
cred = prepare_creds();
if (!cred)
return -ENOMEM;
diff --git a/security/security.c b/security/security.c
index bd4c5f6..e902f3b 100644
--- a/security/security.c
+++ b/security/security.c
@@ -25,6 +25,7 @@
#include <linux/mount.h>
#include <linux/personality.h>
#include <linux/backing-dev.h>
+#include <linux/user_namespace.h>
#include <net/flow.h>

#define MAX_LSM_EVM_XATTR 2
@@ -1541,6 +1542,25 @@ int security_audit_rule_match(u32 secid, u32 field, u32 op, void *lsmrule,
}
#endif /* CONFIG_AUDIT */

+#ifdef CONFIG_SECURITY
+
+int security_userns_create(struct user_namespace *ns)
+{
+ return call_int_hook(userns_create, 0, ns);
+}
+
+void security_userns_free(struct user_namespace *ns)
+{
+ call_void_hook(userns_free, ns);
+}
+
+int security_userns_setns(struct nsproxy *nsproxy, struct user_namespace *ns)
+{
+ return call_int_hook(userns_setns, 0, nsproxy, ns);
+}
+
+#endif /* CONFIG_SECURITY */
+
struct security_hook_heads security_hook_heads = {
.binder_set_context_mgr =
LIST_HEAD_INIT(security_hook_heads.binder_set_context_mgr),
@@ -1885,4 +1905,12 @@ struct security_hook_heads security_hook_heads = {
.audit_rule_free =
LIST_HEAD_INIT(security_hook_heads.audit_rule_free),
#endif /* CONFIG_AUDIT */
+#ifdef CONFIG_SECURITY
+ .userns_create =
+ LIST_HEAD_INIT(security_hook_heads.userns_create),
+ .userns_free =
+ LIST_HEAD_INIT(security_hook_heads.userns_free),
+ .userns_setns =
+ LIST_HEAD_INIT(security_hook_heads.userns_setns),
+#endif /* CONFIG_SECURITY */
};
--
2.1.0