[PATCH bpf-next v1 08/13] bpf: lsm: 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/bpf/bprm_check_security
   bpf_prog1

Signed-off-by: KP Singh <kpsingh@google.com>
---
 security/bpf/lsm_fs.c | 81 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 80 insertions(+), 1 deletion(-)

diff --git a/security/bpf/lsm_fs.c b/security/bpf/lsm_fs.c
index b271e9582d0f..01a89bce1347 100644
--- a/security/bpf/lsm_fs.c
+++ b/security/bpf/lsm_fs.c
@@ -10,6 +10,7 @@
 #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>
 #include <linux/bpf_lsm.h>
@@ -19,7 +20,85 @@
 
 static struct dentry *bpf_lsm_dir;
 
-static const struct file_operations hook_ops = {};
+static void *seq_start(struct seq_file *m, loff_t *pos)
+	__acquires(RCU)
+{
+	struct bpf_prog_array_item *item;
+	struct bpf_prog_array *progs;
+	struct bpf_lsm_hook *h;
+	struct dentry *dentry;
+
+	/*
+	 * 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 (!progs)
+		return NULL;
+
+	/* Assumes that no &dummy_bpf_prog entries exist */
+	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 hook_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, &hook_seq_ops);
+}
+
+static const struct file_operations hook_ops = {
+	.open		= hook_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
 
 int bpf_lsm_fs_initialized;
 
-- 
2.20.1