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Subject[RFC 2/3] LSM: Add statistics about the invocation of dynamic hooks
This patch builds on the dynamic hooks patch. With dynamic hooks,
/sys/kernel/security/lsm doesn't really make a lot of sense, because
the administrator is more likely interested in the per-hook modules.
There is now a /sys/kernel/security/dynamic_hooks/${HOOK_NAME} which
has the currently attached LSMs for that given hook.

Not only does it list which LSMs are hooked into each dynamic hook,
but it also lists the global accept / deny count, as well as the
per-hook accept / deny count. The earlier is useful to keep consistent
statistics across the attachment, and unattachment of LSMs.

Signed-off-by: Sargun Dhillon <sargun@sargun.me>
---
security/Kconfig | 7 +++
security/Makefile | 1 +
security/dynamic.h | 9 ++++
security/dynamicfs.c | 118 +++++++++++++++++++++++++++++++++++++++++++++++++++
security/inode.c | 2 +
5 files changed, 137 insertions(+)
create mode 100644 security/dynamicfs.c

diff --git a/security/Kconfig b/security/Kconfig
index 77841bd..d6c579d 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -94,6 +94,13 @@ config SECURITY_DYNAMIC_HOOKS
They cannot circumvent the built-in LSMs.
If you are unsure how to answer this question, answer N.

+config SECURITY_DYNAMIC_HOOKS_FS
+ bool
+ default y if SECURITY_DYNAMIC_HOOKS && SECURITYFS
+ depends on SECURITY_DYNAMIC_HOOKS && SECURITYFS
+ help
+ This option enables listing of dynamically loaded LSM hooks.
+
config INTEL_TXT
bool "Enable Intel(R) Trusted Execution Technology (Intel(R) TXT)"
depends on HAVE_INTEL_TXT
diff --git a/security/Makefile b/security/Makefile
index 59e695a..51cbec0 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -19,6 +19,7 @@ obj-$(CONFIG_MMU) += min_addr.o
obj-$(CONFIG_SECURITY) += security.o
obj-$(CONFIG_SECURITYFS) += inode.o
obj-$(CONFIG_SECURITY_DYNAMIC_HOOKS) += dynamic.o
+obj-$(CONFIG_SECURITY_DYNAMIC_HOOKS_FS) += dynamicfs.o
obj-$(CONFIG_SECURITY_SELINUX) += selinux/
obj-$(CONFIG_SECURITY_SMACK) += smack/
obj-$(CONFIG_AUDIT) += lsm_audit.o
diff --git a/security/dynamic.h b/security/dynamic.h
index 6823e38..1362b08 100644
--- a/security/dynamic.h
+++ b/security/dynamic.h
@@ -13,6 +13,9 @@ struct dynamic_hook {
struct percpu_counter invocation;
struct percpu_counter deny;
const char *name;
+#ifdef CONFIG_SECURITY_DYNAMIC_HOOKS_FS
+ struct dentry *dentry;
+#endif
struct list_head head;
struct srcu_struct srcu;
};
@@ -22,3 +25,9 @@ extern void security_init_dynamic_hooks(void);
#else
static void security_init_dynamic_hooks(void) {}
#endif
+
+#ifdef CONFIG_SECURITY_DYNAMIC_HOOKS_FS
+extern void securityfs_init_dynamic_hooks(void);
+#else
+static void securityfs_init_dynamic_hooks(void) {}
+#endif
diff --git a/security/dynamicfs.c b/security/dynamicfs.c
new file mode 100644
index 0000000..a9292e2
--- /dev/null
+++ b/security/dynamicfs.c
@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/srcu.h>
+#include <linux/seq_file.h>
+#include <linux/percpu_counter.h>
+#include <linux/percpu.h>
+
+#include "dynamic.h"
+
+struct seq_private_data {
+ struct dynamic_hook *dh;
+ int srcu_lock_index;
+};
+
+static void *dynamic_hooks_sop_start(struct seq_file *s, loff_t *pos)
+{
+ struct seq_private_data *pd = s->private;
+
+ pd->srcu_lock_index = srcu_read_lock(&pd->dh->srcu);
+ return seq_list_start_head(&pd->dh->head, *pos);
+}
+
+static void *dynamic_hooks_sop_next(struct seq_file *s, void *v, loff_t *pos)
+{
+ struct seq_private_data *pd = s->private;
+
+ return seq_list_next(v, &pd->dh->head, pos);
+}
+
+static int dynamic_hooks_sop_show(struct seq_file *s, void *v)
+{
+ struct seq_private_data *pd = s->private;
+ struct dynamic_security_hook *dsh;
+
+ if (v == (void *)&pd->dh->head) {
+ seq_puts(s, "name\tinvocations\tdenies\n");
+ seq_printf(s, "all\t%lld\t%lld\n",
+ percpu_counter_sum(&pd->dh->invocation),
+ percpu_counter_sum(&pd->dh->deny));
+ return 0;
+ }
+
+ dsh = list_entry(v, typeof(*dsh), list);
+ seq_printf(s, "%s\t%lld\t%lld\n", dsh->lsm,
+ percpu_counter_sum(&dsh->invocation),
+ percpu_counter_sum(&dsh->deny));
+
+ return 0;
+}
+
+static void dynamic_hooks_sop_stop(struct seq_file *s, void *v)
+{
+ struct seq_private_data *pd = s->private;
+
+ srcu_read_unlock(&pd->dh->srcu, pd->srcu_lock_index);
+}
+
+static const struct seq_operations dynamic_hooks_sops = {
+ .start = dynamic_hooks_sop_start,
+ .next = dynamic_hooks_sop_next,
+ .show = dynamic_hooks_sop_show,
+ .stop = dynamic_hooks_sop_stop,
+};
+
+static int security_dynamic_hook_open(struct inode *inode, struct file *file)
+{
+ struct seq_private_data *pd;
+
+ pd = (struct seq_private_data *)__seq_open_private(file,
+ &dynamic_hooks_sops,
+ sizeof(*pd));
+
+ if (!pd)
+ return -ENOMEM;
+
+ pd->dh = inode->i_private;
+
+ return 0;
+}
+
+static const struct file_operations dynamic_hooks_fops = {
+ .open = security_dynamic_hook_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
+static struct dentry *dynamic_hooks_dir;
+void securityfs_init_dynamic_hooks(void)
+{
+ struct dynamic_hook *dh;
+ int i;
+
+ dynamic_hooks_dir = securityfs_create_dir("dynamic_hooks", NULL);
+ if (IS_ERR(dynamic_hooks_dir)) {
+ pr_err("Unable to create dynamic hooks LSM directory - %ld\n",
+ PTR_ERR(dynamic_hooks_dir));
+ return;
+ }
+
+ for (i = 0; i < __MAX_DYNAMIC_SECURITY_HOOK; i++) {
+
+ dh = &dynamic_hooks[i];
+ dh->dentry = securityfs_create_file(dh->name, 0444,
+ dynamic_hooks_dir, dh,
+ &dynamic_hooks_fops);
+ if (IS_ERR(dh->dentry))
+ goto err;
+ }
+ return;
+
+err:
+ pr_err("Unable to create dynamic hook directory - %s - %ld\n",
+ dh->name, PTR_ERR(dh->dentry));
+}
diff --git a/security/inode.c b/security/inode.c
index 8dd9ca8..0862be1 100644
--- a/security/inode.c
+++ b/security/inode.c
@@ -22,6 +22,7 @@
#include <linux/security.h>
#include <linux/lsm_hooks.h>
#include <linux/magic.h>
+#include "dynamic.h"

static struct vfsmount *mount;
static int mount_count;
@@ -335,6 +336,7 @@ static int __init securityfs_init(void)
sysfs_remove_mount_point(kernel_kobj, "security");
return retval;
}
+ securityfs_init_dynamic_hooks();
#ifdef CONFIG_SECURITY
lsm_dentry = securityfs_create_file("lsm", 0444, NULL, NULL,
&lsm_ops);
--
2.9.3
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