ebpf: add prandom helper for packet sampling

This work is similar to commit 4cd3675ebf74 ("filter: added BPF
random opcode") and adds a possibility for packet sampling in eBPF.

Currently, this is only possible in classic BPF and useful to
combine sampling with f.e. packet sockets, possible also with tc.

Example function proto-type looks like:

  u32 (*prandom_u32)(void) = (void *)BPF_FUNC_get_prandom_u32;

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 80f2e0f..50bf95e 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -154,4 +154,6 @@ extern const struct bpf_func_proto bpf_map_lookup_elem_proto;
 extern const struct bpf_func_proto bpf_map_update_elem_proto;
 extern const struct bpf_func_proto bpf_map_delete_elem_proto;
 
+extern const struct bpf_func_proto bpf_get_prandom_u32_proto;
+
 #endif /* _LINUX_BPF_H */

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 3fa1af8..1c2ca2b 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -165,6 +165,7 @@ enum bpf_func_id {
        BPF_FUNC_map_lookup_elem, /* void *map_lookup_elem(&map, &key) */
        BPF_FUNC_map_update_elem, /* int map_update_elem(&map, &key, &value, flags) */
        BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */
+       BPF_FUNC_get_prandom_u32, /* u32 prandom_u32(void) */
        __BPF_FUNC_MAX_ID,
 };
 

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 50603ae..c1dbbb5 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -661,6 +661,8 @@ const struct bpf_func_proto bpf_map_lookup_elem_proto __weak;
 const struct bpf_func_proto bpf_map_update_elem_proto __weak;
 const struct bpf_func_proto bpf_map_delete_elem_proto __weak;
 
+const struct bpf_func_proto bpf_get_prandom_u32_proto __weak;
+
 /* To execute LD_ABS/LD_IND instructions __bpf_prog_run() may call
  * skb_copy_bits(), so provide a weak definition of it for NET-less config.
  */

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index a3c7701..95eb59a 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -11,6 +11,7 @@
  */
 #include <linux/bpf.h>
 #include <linux/rcupdate.h>
+#include <linux/random.h>
 
 /* If kernel subsystem is allowing eBPF programs to call this function,
  * inside its own verifier_ops->get_func_proto() callback it should return
@@ -87,3 +88,14 @@ const struct bpf_func_proto bpf_map_delete_elem_proto = {
        .arg1_type = ARG_CONST_MAP_PTR,
        .arg2_type = ARG_PTR_TO_MAP_KEY,
 };
+
+static u64 bpf_get_prandom_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+       return prandom_u32();
+}
+
+const struct bpf_func_proto bpf_get_prandom_u32_proto = {
+       .func           = bpf_get_prandom_u32,
+       .gpl_only       = false,
+       .ret_type       = RET_INTEGER,
+};

diff --git a/net/core/filter.c b/net/core/filter.c
index 7a4eb70..4344db3 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1139,6 +1139,8 @@ sk_filter_func_proto(enum bpf_func_id func_id)
                return &bpf_map_update_elem_proto;
        case BPF_FUNC_map_delete_elem:
                return &bpf_map_delete_elem_proto;
+       case BPF_FUNC_get_prandom_u32:
+               return &bpf_get_prandom_u32_proto;
        default:
                return NULL;
        }