selftests/bpf: add a test for device cgroup controller

Add a test for device cgroup controller.

The test loads a simple bpf program which logs all
device access attempts using trace_printk() and forbids
all operations except operations with /dev/zero and
/dev/urandom.

Then the test creates and joins a test cgroup, and attaches
the bpf program to it.

Then it tries to perform some simple device operations
and checks the result:

  create /dev/null (should fail)
  create /dev/zero (should pass)
  copy data from /dev/urandom to /dev/zero (should pass)
  copy data from /dev/urandom to /dev/full (should fail)
  copy data from /dev/random to /dev/zero (should fail)

Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 60 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/dev_cgroup.c b/tools/testing/selftests/bpf/dev_cgroup.c
new file mode 100644
index 000000000000..ce41a3475f27
--- /dev/null
+++ b/tools/testing/selftests/bpf/dev_cgroup.c
@@ -0,0 +1,60 @@
+/* Copyright (c) 2017 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+
+#include <linux/bpf.h>
+#include <linux/version.h>
+#include "bpf_helpers.h"
+
+SEC("cgroup/dev")
+int bpf_prog1(struct bpf_cgroup_dev_ctx *ctx)
+{
+	short type = ctx->access_type & 0xFFFF;
+#ifdef DEBUG
+	short access = ctx->access_type >> 16;
+	char fmt[] = "  %d:%d    \n";
+
+	switch (type) {
+	case BPF_DEVCG_DEV_BLOCK:
+		fmt[0] = 'b';
+		break;
+	case BPF_DEVCG_DEV_CHAR:
+		fmt[0] = 'c';
+		break;
+	default:
+		fmt[0] = '?';
+		break;
+	}
+
+	if (access & BPF_DEVCG_ACC_READ)
+		fmt[8] = 'r';
+
+	if (access & BPF_DEVCG_ACC_WRITE)
+		fmt[9] = 'w';
+
+	if (access & BPF_DEVCG_ACC_MKNOD)
+		fmt[10] = 'm';
+
+	bpf_trace_printk(fmt, sizeof(fmt), ctx->major, ctx->minor);
+#endif
+
+	/* Allow access to /dev/zero and /dev/random.
+	 * Forbid everything else.
+	 */
+	if (ctx->major != 1 || type != BPF_DEVCG_DEV_CHAR)
+		return 0;
+
+	switch (ctx->minor) {
+	case 5: /* 1:5 /dev/zero */
+	case 9: /* 1:9 /dev/urandom */
+		return 1;
+	}
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
+__u32 _version SEC("version") = LINUX_VERSION_CODE;