blackhole_dev: add a selftest

Since this is not really a device with all capabilities, this test
ensures that it has *enough* to make it through the data path
without causing unwanted side-effects (read crash!).

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 110 insertions, 0 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cbdfae379896..99272b5dd980 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1909,6 +1909,15 @@ config TEST_BPF
 
 	  If unsure, say N.
 
+config TEST_BLACKHOLE_DEV
+	tristate "Test blackhole netdev functionality"
+	depends on m && NET
+	help
+	  This builds the "test_blackhole_dev" module that validates the
+	  data path through this blackhole netdev.
+
+	  If unsure, say N.
+
 config FIND_BIT_BENCHMARK
 	tristate "Test find_bit functions"
 	help
diff --git a/lib/Makefile b/lib/Makefile
index dcb558c7554d..6ac44fe2a37f 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -91,6 +91,7 @@ obj-$(CONFIG_TEST_DEBUG_VIRTUAL) += test_debug_virtual.o
 obj-$(CONFIG_TEST_MEMCAT_P) += test_memcat_p.o
 obj-$(CONFIG_TEST_OBJAGG) += test_objagg.o
 obj-$(CONFIG_TEST_STACKINIT) += test_stackinit.o
+obj-$(CONFIG_TEST_BLACKHOLE_DEV) += test_blackhole_dev.o
 
 obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
 
diff --git a/lib/test_blackhole_dev.c b/lib/test_blackhole_dev.c
new file mode 100644
index 000000000000..4c40580a99a3
--- /dev/null
+++ b/lib/test_blackhole_dev.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This module tests the blackhole_dev that is created during the
+ * net subsystem initialization. The test this module performs is
+ * by injecting an skb into the stack with skb->dev as the
+ * blackhole_dev and expects kernel to behave in a sane manner
+ * (in other words, *not crash*)!
+ *
+ * Copyright (c) 2018, Mahesh Bandewar <maheshb@google.com>
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <linux/udp.h>
+#include <linux/ipv6.h>
+
+#include <net/dst.h>
+
+#define SKB_SIZE  256
+#define HEAD_SIZE (14+40+8)	/* Ether + IPv6 + UDP */
+#define TAIL_SIZE 32		/* random tail-room */
+
+#define UDP_PORT 1234
+
+static int __init test_blackholedev_init(void)
+{
+	struct ipv6hdr *ip6h;
+	struct sk_buff *skb;
+	struct ethhdr *ethh;
+	struct udphdr *uh;
+	int data_len;
+	int ret;
+
+	skb = alloc_skb(SKB_SIZE, GFP_KERNEL);
+	if (!skb)
+		return -ENOMEM;
+
+	/* Reserve head-room for the headers */
+	skb_reserve(skb, HEAD_SIZE);
+
+	/* Add data to the skb */
+	data_len = SKB_SIZE - (HEAD_SIZE + TAIL_SIZE);
+	memset(__skb_put(skb, data_len), 0xf, data_len);
+
+	/* Add protocol data */
+	/* (Transport) UDP */
+	uh = (struct udphdr *)skb_push(skb, sizeof(struct udphdr));
+	skb_set_transport_header(skb, 0);
+	uh->source = uh->dest = htons(UDP_PORT);
+	uh->len = htons(data_len);
+	uh->check = 0;
+	/* (Network) IPv6 */
+	ip6h = (struct ipv6hdr *)skb_push(skb, sizeof(struct ipv6hdr));
+	skb_set_network_header(skb, 0);
+	ip6h->hop_limit = 32;
+	ip6h->payload_len = data_len + sizeof(struct udphdr);
+	ip6h->nexthdr = IPPROTO_UDP;
+	ip6h->saddr = in6addr_loopback;
+	ip6h->daddr = in6addr_loopback;
+	/* Ether */
+	ethh = (struct ethhdr *)skb_push(skb, sizeof(struct ethhdr));
+	skb_set_mac_header(skb, 0);
+
+	skb->protocol = htons(ETH_P_IPV6);
+	skb->pkt_type = PACKET_HOST;
+	skb->dev = blackhole_netdev;
+
+	/* Now attempt to send the packet */
+	ret = dev_queue_xmit(skb);
+
+	switch (ret) {
+	case NET_XMIT_SUCCESS:
+		pr_warn("dev_queue_xmit() returned NET_XMIT_SUCCESS\n");
+		break;
+	case NET_XMIT_DROP:
+		pr_warn("dev_queue_xmit() returned NET_XMIT_DROP\n");
+		break;
+	case NET_XMIT_CN:
+		pr_warn("dev_queue_xmit() returned NET_XMIT_CN\n");
+		break;
+	default:
+		pr_err("dev_queue_xmit() returned UNKNOWN(%d)\n", ret);
+	}
+
+	return 0;
+}
+
+static void __exit test_blackholedev_exit(void)
+{
+	pr_warn("test_blackholedev module terminating.\n");
+}
+
+module_init(test_blackholedev_init);
+module_exit(test_blackholedev_exit);
+
+MODULE_AUTHOR("Mahesh Bandewar <maheshb@google.com>");
+MODULE_LICENSE("GPL");