1 files changed, 82 insertions, 0 deletions
diff --git a/src/core/bpf/restrict_fs/restrict-fs.bpf.c b/src/core/bpf/restrict_fs/restrict-fs.bpf.c
new file mode 100644
index 0000000..eb5ed3e
--- /dev/null
+++ b/src/core/bpf/restrict_fs/restrict-fs.bpf.c
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+/* The SPDX header above is actually correct in claiming this was
+ * LGPL-2.1-or-later, because it is. Since the kernel doesn't consider that
+ * compatible with GPL we will claim this to be GPL however, which should be
+ * fine given that LGPL-2.1-or-later downgrades to GPL if needed.
+ */
+
+#include <linux/types.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_core_read.h>
+#include <errno.h>
+#include <stddef.h>
+#include <stdint.h>
+
+struct super_block {
+        unsigned long int s_magic;
+} __attribute__((preserve_access_index));
+
+struct inode {
+        struct super_block *i_sb;
+} __attribute__((preserve_access_index));
+
+struct file {
+        struct inode *f_inode;
+} __attribute__((preserve_access_index));
+
+/*
+ * max_entries is set from user space with the bpf_map__set_max_entries helper.
+ * */
+struct {
+        __uint(type, BPF_MAP_TYPE_HASH_OF_MAPS);
+        __type(key, uint64_t);      /* cgroup ID */
+        __type(value, uint32_t);    /* fs magic set */
+} cgroup_hash SEC(".maps");
+
+SEC("lsm/file_open")
+int BPF_PROG(restrict_filesystems, struct file *file, int ret)
+{
+        unsigned long raw_magic_number;
+        uint64_t cgroup_id;
+        uint32_t *value, *magic_map, magic_number, zero = 0, *is_allow;
+
+        /* ret is the return value from the previous BPF program or 0 if it's
+         * the first hook */
+        if (ret != 0)
+                return ret;
+
+        BPF_CORE_READ_INTO(&raw_magic_number, file, f_inode, i_sb, s_magic);
+        /* super_block.s_magic is unsigned long, but magic_map keys are
+         * uint32_t. Using s_magic as-is would fail on big-endian systems,
+         * which have 64-bit unsigned long. So cast it. */
+        magic_number = (uint32_t)raw_magic_number;
+
+        cgroup_id = bpf_get_current_cgroup_id();
+
+        magic_map = bpf_map_lookup_elem(&cgroup_hash, &cgroup_id);
+        if (!magic_map)
+                return 0;
+
+        is_allow = bpf_map_lookup_elem(magic_map, &zero);
+        if (!is_allow)
+                /* Malformed map, it doesn't include whether it's an allow list
+                 * or a deny list. Allow. */
+                return 0;
+
+        if (*is_allow) {
+                /* Allow-list: Allow access only if magic_number present in inner map */
+                if (!bpf_map_lookup_elem(magic_map, &magic_number))
+                        return -EPERM;
+        } else {
+                /* Deny-list: Allow access only if magic_number is not present in inner map */
+                if (bpf_map_lookup_elem(magic_map, &magic_number))
+                        return -EPERM;
+        }
+
+        return 0;
+}
+
+static const char _license[] SEC("license") = "GPL";