samples/bpf: Add test/example of using bpf_probe_write_user bpf helper

[deliverable/linux.git] / samples / bpf / test_probe_write_user_kern.c

diff --git a/samples/bpf/test_probe_write_user_kern.c b/samples/bpf/test_probe_write_user_kern.c
new file mode 100644 (file)
index 0000000..3a677c8
--- /dev/null
+++ b/samples/bpf/test_probe_write_user_kern.c
@@ -0,0 +1,52 @@
+/* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me>
+ *
+ * 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/skbuff.h>
+#include <linux/netdevice.h>
+#include <uapi/linux/bpf.h>
+#include <linux/version.h>
+#include "bpf_helpers.h"
+
+struct bpf_map_def SEC("maps") dnat_map = {
+       .type = BPF_MAP_TYPE_HASH,
+       .key_size = sizeof(struct sockaddr_in),
+       .value_size = sizeof(struct sockaddr_in),
+       .max_entries = 256,
+};
+
+/* kprobe is NOT a stable ABI
+ * kernel functions can be removed, renamed or completely change semantics.
+ * Number of arguments and their positions can change, etc.
+ * In such case this bpf+kprobe example will no longer be meaningful
+ *
+ * This example sits on a syscall, and the syscall ABI is relatively stable
+ * of course, across platforms, and over time, the ABI may change.
+ */
+SEC("kprobe/sys_connect")
+int bpf_prog1(struct pt_regs *ctx)
+{
+       struct sockaddr_in new_addr, orig_addr = {};
+       struct sockaddr_in *mapped_addr;
+       void *sockaddr_arg = (void *)PT_REGS_PARM2(ctx);
+       int sockaddr_len = (int)PT_REGS_PARM3(ctx);
+
+       if (sockaddr_len > sizeof(orig_addr))
+               return 0;
+
+       if (bpf_probe_read(&orig_addr, sizeof(orig_addr), sockaddr_arg) != 0)
+               return 0;
+
+       mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr);
+       if (mapped_addr != NULL) {
+               memcpy(&new_addr, mapped_addr, sizeof(new_addr));
+               bpf_probe_write_user(sockaddr_arg, &new_addr,
+                                    sizeof(new_addr));
+       }
+       return 0;
+}
+
+char _license[] SEC("license") = "GPL";
+u32 _version SEC("version") = LINUX_VERSION_CODE;