From: Stefan Berger <stefanb@linux.ibm.com>

Introduce the IMA_NS in Kconfig for IMA namespace enablement.

Enable the lazy initialization of an IMA namespace when a user mounts
SecurityFS. Now a user_namespace will get a pointer to an ima_namespace
and therefore add an implementation of get_current_ns() that returns this
pointer.

get_current_ns() may now return a NULL pointer for as long as the IMA
namespace hasn't been created, yet. Therefore, return early from those
functions that may now get a NULL pointer from this call. The NULL
pointer can typically be treated similar to not having an IMA policy set
and simply return early from a function.

Implement ima_ns_from_file() for SecurityFS-related files where we can
now get the IMA namespace via the user namespace pointer associated
with the superblock of the SecurityFS filesystem instance. Since
the functions using ima_ns_from_file() will only be called after an
ima_namesapce has been allocated they will never get a NULL pointer
for the ima_namespace.

Switch access to userns->ima_ns to use acquire/release semantics to ensure
that a newly created ima_namespace structure is fully visible upon access.

Replace usage of current_user_ns() with ima_ns_from_user_ns() that
implements a method to derive the user_namespace from the given
ima_namespace. It leads to the same result.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 include/linux/ima.h                 |  9 ++++++-
 init/Kconfig                        | 13 ++++++++++
 kernel/user_namespace.c             |  2 ++
 security/integrity/ima/ima.h        | 35 ++++++++++++++++++++++-----
 security/integrity/ima/ima_fs.c     | 37 ++++++++++++++++++++++-------
 security/integrity/ima/ima_main.c   | 29 ++++++++++++++++------
 security/integrity/ima/ima_ns.c     |  3 ++-
 security/integrity/ima/ima_policy.c | 13 +++++-----
 8 files changed, 112 insertions(+), 29 deletions(-)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 5354e83d1694..7b9713b290ae 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h

@@ -11,6 +11,7 @@
 #include <linux/fs.h>
 #include <linux/security.h>
 #include <linux/kexec.h>
+#include <linux/user_namespace.h>
 #include <crypto/hash_info.h>
 struct linux_binprm;
 

@@ -71,7 +72,13 @@ static inline const char * const *arch_get_ima_policy(void)
 static inline struct user_namespace
 *ima_ns_to_user_ns(struct ima_namespace *ns)
 {
-	return current_user_ns();
+	struct user_namespace *user_ns;
+
+	user_ns = current_user_ns();
+#ifdef CONFIG_IMA_NS
+	WARN_ON(user_ns->ima_ns != ns);
+#endif
+	return user_ns;
 }
 
 #else

diff --git a/init/Kconfig b/init/Kconfig
index 4b7bac10c72d..e27155e0ddba 100644
--- a/init/Kconfig
+++ b/init/Kconfig

@@ -1247,6 +1247,19 @@ config NET_NS
 	  Allow user space to create what appear to be multiple instances
 	  of the network stack.
 
+config IMA_NS
+	bool "IMA namespace"
+	depends on USER_NS
+	depends on IMA
+	default n
+	help
+	  Allow the creation of an IMA namespace for each user namespace.
+	  Namespaced IMA enables having IMA features work separately
+	  in each IMA namespace.
+	  Currently, only the audit status flags are stored in the namespace,
+	  which allows the same file to be audited each time it is accessed
+	  in a new namespace.
+
 endif # NAMESPACES
 
 config CHECKPOINT_RESTORE

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 6b2e3ca7ee99..653f8fa83b69 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c

@@ -20,6 +20,7 @@
 #include <linux/fs_struct.h>
 #include <linux/bsearch.h>
 #include <linux/sort.h>
+#include <linux/ima.h>
 
 static struct kmem_cache *user_ns_cachep __read_mostly;
 static DEFINE_MUTEX(userns_state_mutex);

@@ -196,6 +197,7 @@ static void free_user_ns(struct work_struct *work)
 			kfree(ns->projid_map.forward);
 			kfree(ns->projid_map.reverse);
 		}
+		free_ima_ns(ns);
 		retire_userns_sysctls(ns);
 		key_free_user_ns(ns);
 		ns_free_inum(&ns->ns);

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 344c8c4bd030..d993655ec796 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h

@@ -509,21 +509,20 @@ struct user_namespace *ima_user_ns_from_file(const struct file *filp)
 	return file_inode(filp)->i_sb->s_user_ns;
 }
 
+#ifdef CONFIG_IMA_NS
+
 static inline struct ima_namespace
 *ima_ns_from_user_ns(struct user_namespace *user_ns)
 {
-	if (user_ns == &init_user_ns)
-		return &init_ima_ns;
-	return NULL;
+	/* Pairs with smp_store_releases() in create_ima_ns(). */
+	return smp_load_acquire(&user_ns->ima_ns);
 }
 
 static inline struct ima_namespace *get_current_ns(void)
 {
-	return &init_ima_ns;
+	return ima_ns_from_user_ns(current_user_ns());
 }
 
-#ifdef CONFIG_IMA_NS
-
 struct ima_namespace *create_ima_ns(struct user_namespace *user_ns);
 
 struct ns_status *ima_get_ns_status(struct ima_namespace *ns,

@@ -532,6 +531,11 @@ struct ns_status *ima_get_ns_status(struct ima_namespace *ns,
 
 void ima_free_ns_status_tree(struct ima_namespace *ns);
 
+static inline struct ima_namespace *ima_ns_from_file(const struct file *filp)
+{
+	return ima_user_ns_from_file(filp)->ima_ns;
+}
+
 #define IMA_NS_STATUS_ACTIONS   IMA_AUDIT
 #define IMA_NS_STATUS_FLAGS     IMA_AUDITED
 

@@ -542,6 +546,20 @@ unsigned long set_iint_flags(struct integrity_iint_cache *iint,
 
 #else
 
+static inline struct ima_namespace
+*ima_ns_from_user_ns(struct user_namespace *user_ns)
+{
+	if (user_ns == &init_user_ns)
+		return &init_ima_ns;
+	return NULL;
+}
+
+
+static inline struct ima_namespace *get_current_ns(void)
+{
+	return &init_ima_ns;
+}
+
 static inline struct ima_namespace *
 create_ima_ns(struct user_namespace *user_ns)
 {

@@ -572,6 +590,11 @@ static inline unsigned long set_iint_flags(struct integrity_iint_cache *iint,
 	return flags;
 }
 
+static inline struct ima_namespace *ima_ns_from_file(const struct file *filp)
+{
+	return &init_ima_ns;
+}
+
 #endif /* CONFIG_IMA_NS */
 
 #endif /* __LINUX_IMA_H */

diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 468508f6a7e8..ee3af81d1c3e 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c

@@ -49,7 +49,7 @@ static ssize_t ima_show_htable_violations(struct file *filp,
 					  char __user *buf,
 					  size_t count, loff_t *ppos)
 {
-	struct ima_namespace *ns = &init_ima_ns;
+	struct ima_namespace *ns = ima_ns_from_file(filp);
 
 	return ima_show_htable_value(buf, count, ppos,
 				     &ns->ima_htable.violations);

@@ -64,7 +64,7 @@ static ssize_t ima_show_measurements_count(struct file *filp,
 					   char __user *buf,
 					   size_t count, loff_t *ppos)
 {
-	struct ima_namespace *ns = &init_ima_ns;
+	struct ima_namespace *ns = ima_ns_from_file(filp);
 
 	return ima_show_htable_value(buf, count, ppos, &ns->ima_htable.len);
 }

@@ -77,7 +77,7 @@ static const struct file_operations ima_measurements_count_ops = {
 /* returns pointer to hlist_node */
 static void *ima_measurements_start(struct seq_file *m, loff_t *pos)
 {
-	struct ima_namespace *ns = &init_ima_ns;
+	struct ima_namespace *ns = ima_ns_from_file(m->file);
 	loff_t l = *pos;
 	struct ima_queue_entry *qe;
 

@@ -95,7 +95,7 @@ static void *ima_measurements_start(struct seq_file *m, loff_t *pos)
 
 static void *ima_measurements_next(struct seq_file *m, void *v, loff_t *pos)
 {
-	struct ima_namespace *ns = &init_ima_ns;
+	struct ima_namespace *ns = ima_ns_from_file(m->file);
 	struct ima_queue_entry *qe = v;
 
 	/* lock protects when reading beyond last element

@@ -317,7 +317,7 @@ static ssize_t ima_read_policy(struct ima_namespace *ns, char *path)
 static ssize_t ima_write_policy(struct file *file, const char __user *buf,
 				size_t datalen, loff_t *ppos)
 {
-	struct ima_namespace *ns = &init_ima_ns;
+	struct ima_namespace *ns = ima_ns_from_file(file);
 	char *data;
 	ssize_t result;
 

@@ -379,7 +379,7 @@ static const struct seq_operations ima_policy_seqops = {
 static int ima_open_policy(struct inode *inode, struct file *filp)
 {
 	struct user_namespace *user_ns = ima_user_ns_from_file(filp);
-	struct ima_namespace *ns = &init_ima_ns;
+	struct ima_namespace *ns = ima_ns_from_file(filp);
 
 	if (!(filp->f_flags & O_WRONLY)) {
 #ifndef	CONFIG_IMA_READ_POLICY

@@ -406,7 +406,7 @@ static int ima_open_policy(struct inode *inode, struct file *filp)
  */
 static int ima_release_policy(struct inode *inode, struct file *file)
 {
-	struct ima_namespace *ns = &init_ima_ns;
+	struct ima_namespace *ns = ima_ns_from_file(file);
 	const char *cause = ns->valid_policy ? "completed" : "failed";
 
 	if ((file->f_flags & O_ACCMODE) == O_RDONLY)

@@ -459,12 +459,29 @@ int ima_fs_ns_init(struct user_namespace *user_ns, struct dentry *root)
 	struct dentry *ascii_runtime_measurements = NULL;
 	struct dentry *runtime_measurements_count = NULL;
 	struct dentry *violations = NULL;
+	bool created_ns = false;
+
+	/*
+	 * While multiple superblocks can exist they are keyed by userns in
+	 * s_fs_info for securityfs. The first time a userns mounts a
+	 * securityfs instance we lazily allocate the ima_namespace for the
+	 * userns since that's the only way a userns can meaningfully use ima.
+	 * The vfs ensures we're the only one to call fill_super() and hence
+	 * ima_fs_ns_init(), so we don't need any memory barriers here, i.e.
+	 * user_ns->ima_ns can't change while we're in here.
+	 */
+	if (!ns) {
+		ns = create_ima_ns(user_ns);
+		if (IS_ERR(ns))
+			return PTR_ERR(ns);
+		created_ns = true;
+	}