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Subject[PATCH bpf-next v1 08/13] bpf: lsm: Show attached program names in hook read handler.
Date
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
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