Re: [PATCH v8 19/19] ima: Enable IMA namespaces
From: Stefan Berger
Date: Tue Jan 18 2022 - 12:54:26 EST
On 1/14/22 07:05, Christian Brauner wrote:
On Tue, Jan 04, 2022 at 12:04:16PM -0500, Stefan Berger wrote:
From: Stefan Berger <stefanb@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
---
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;
+ }
Since create_ima_ns() initializes user_ns->ima_ns via
smp_store_release() the patch currently implies that concurrent access
to user_ns->ima_ns are safe once create_ima_ns() returns.
Specifically, it entails that no caller will access entries in the ima
namespace that will only be filled in past this point. Afaict, this only
relates to the ns->policy_dentry which can't be accessed until
securityfs is finished.
Nonetheless, I would recommend that you change create_ima_ns() to not
initialize user_ns->ima_ns and instead defer this until everything in
the namespace is setup. So maybe move the smp_store_release() to the end
of ima_fs_ns_init(). If ns->policy_dentry wouldn't be stashed in ima_ns
it wouldn't matter but since it is I would not publish ima_ns before
this is set. Sm like (uncompiled, untested):
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index ee3af81d1c3e..64ca47671d31 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -531,6 +531,8 @@ int ima_fs_ns_init(struct user_namespace *user_ns, struct dentry *root)
goto out;
}
+ if (!user_ns->ima_ns)
+ smp_store_release(&user_ns->ima_ns, ns);
return 0;
out:
securityfs_remove(ns->policy_dentry);
As a side-effect this will let you get rid of the bool created_ns and
thereby simplify the codeflow.
Fixed. Thanks.
(Note, that obviously means that the changes I mentioned earlier in
https://lore.kernel.org/containers/20220114114321.7prnt72ukvch4wxa@wittgenstein
can't be made.)