[RFC v1 08/14] krsi: Show attached program names in hook read handler.

[KP Singh <kpsingh@chromium.org>]

From: KP Singh <kpsingh@google.com>

For inspectability the system administrator should be able to view the
list of active KRSI programs:

   bash # cat /sys/kernel/security/krsi/process_execution
   bpf_prog1

Signed-off-by: KP Singh <kpsingh@google.com>
---
 security/krsi/krsi_fs.c | 76 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 75 insertions(+), 1 deletion(-)

diff --git a/security/krsi/krsi_fs.c b/security/krsi/krsi_fs.c
index 3ba18b52ce85..0ebf4fabe935 100644
--- a/security/krsi/krsi_fs.c
+++ b/security/krsi/krsi_fs.c
@@ -6,6 +6,7 @@
 #include <linux/fs.h>
 #include <linux/types.h>
 #include <linux/filter.h>
+#include <linux/seq_file.h>
 #include <linux/bpf.h>
 #include <linux/security.h>
 
@@ -16,8 +17,81 @@ extern struct krsi_hook krsi_hooks_list[];
 
 static struct dentry *krsi_dir;
 
+static void *seq_start(struct seq_file *m, loff_t *pos)
+	__acquires(rcu)
+{
+	struct krsi_hook *h;
+	struct dentry *dentry;
+	struct bpf_prog_array *progs;
+	struct bpf_prog_array_item *item;
+
+	/*
+	 * rcu_read_lock() must be held before any return statement
+	 * because the stop() will always be called and thus call
+	 * rcu_read_unlock()
+	 */
+	rcu_read_lock();
+
+	dentry = file_dentry(m->file);
+	h = dentry->d_fsdata;
+	if (WARN_ON(!h))
+		return ERR_PTR(-EFAULT);
+
+	progs = rcu_dereference(h->progs);
+	if ((*pos) >= bpf_prog_array_length(progs))
+		return NULL;
+
+	item = progs->items + *pos;
+	if (!item->prog)
+		return NULL;
+
+	return item;
+}
+
+static void *seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct bpf_prog_array_item *item = v;
+
+	item++;
+	++*pos;
+
+	if (!item->prog)
+		return NULL;
+
+	return item;
+}
+
+static void seq_stop(struct seq_file *m, void *v)
+	__releases(rcu)
+{
+	rcu_read_unlock();
+}
+
+static int show_prog(struct seq_file *m, void *v)
+{
+	struct bpf_prog_array_item *item = v;
+
+	seq_printf(m, "%s\n", item->prog->aux->name);
+	return 0;
+}
+
+static const struct seq_operations seq_ops = {
+	.show	= show_prog,
+	.start	= seq_start,
+	.next	= seq_next,
+	.stop	= seq_stop,
+};
+
+static int hook_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &seq_ops);
+}
+
 static const struct file_operations krsi_hook_ops = {
-	.llseek = generic_file_llseek,
+	.open		= hook_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
 };
 
 int krsi_fs_initialized;
-- 
2.20.1