bpf: Enable bpf_{g,s}etsockopt in BPF_CGROUP_UDP{4,6}_SENDMSG

Can be used to query/modify socket state for unconnected UDP sendmsg.
Those hooks run as BPF_CGROUP_RUN_SA_PROG_LOCK and operate on
a locked socket.
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210127232853.3753823-2-sdf@google.com

net/core/filter.c

@@ -7023,6 +7023,8 @@ sock_addr_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		case BPF_CGROUP_INET6_BIND:
 		case BPF_CGROUP_INET4_CONNECT:
 		case BPF_CGROUP_INET6_CONNECT:
+		case BPF_CGROUP_UDP4_SENDMSG:
+		case BPF_CGROUP_UDP6_SENDMSG:
 			return &bpf_sock_addr_setsockopt_proto;
 		default:
 			return NULL;
@@ -7033,6 +7035,8 @@ sock_addr_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		case BPF_CGROUP_INET6_BIND:
 		case BPF_CGROUP_INET4_CONNECT:
 		case BPF_CGROUP_INET6_CONNECT:
+		case BPF_CGROUP_UDP4_SENDMSG:
+		case BPF_CGROUP_UDP6_SENDMSG:
 			return &bpf_sock_addr_getsockopt_proto;
 		default:
 			return NULL;

tools/testing/selftests/bpf/bpf_sockopt_helpers.h

+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <sys/socket.h>
+#include <bpf/bpf_helpers.h>
+
+int get_set_sk_priority(void *ctx)
+{
+	int prio;
+
+	/* Verify that context allows calling bpf_getsockopt and
+	 * bpf_setsockopt by reading and writing back socket
+	 * priority.
+	 */
+
+	if (bpf_getsockopt(ctx, SOL_SOCKET, SO_PRIORITY, &prio, sizeof(prio)))
+		return 0;
+	if (bpf_setsockopt(ctx, SOL_SOCKET, SO_PRIORITY, &prio, sizeof(prio)))
+		return 0;
+
+	return 1;
+}

tools/testing/selftests/bpf/progs/sendmsg4_prog.c

@@ -8,6 +8,8 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
 
+#include <bpf_sockopt_helpers.h>
+
 #define SRC1_IP4		0xAC100001U /* 172.16.0.1 */
 #define SRC2_IP4		0x00000000U
 #define SRC_REWRITE_IP4		0x7f000004U
@@ -21,9 +23,14 @@ int _version SEC("version") = 1;
 SEC("cgroup/sendmsg4")
 int sendmsg_v4_prog(struct bpf_sock_addr *ctx)
 {
+	int prio;
+
 	if (ctx->type != SOCK_DGRAM)
 		return 0;
 
+	if (!get_set_sk_priority(ctx))
+		return 0;
+
 	/* Rewrite source. */
 	if (ctx->msg_src_ip4 == bpf_htonl(SRC1_IP4) ||
 	    ctx->msg_src_ip4 == bpf_htonl(SRC2_IP4)) {

tools/testing/selftests/bpf/progs/sendmsg6_prog.c

@@ -8,6 +8,8 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
 
+#include <bpf_sockopt_helpers.h>
+
 #define SRC_REWRITE_IP6_0	0
 #define SRC_REWRITE_IP6_1	0
 #define SRC_REWRITE_IP6_2	0
@@ -28,6 +30,9 @@ int sendmsg_v6_prog(struct bpf_sock_addr *ctx)
 	if (ctx->type != SOCK_DGRAM)
 		return 0;
 
+	if (!get_set_sk_priority(ctx))
+		return 0;
+
 	/* Rewrite source. */
 	if (ctx->msg_src_ip6[3] == bpf_htonl(1) ||
 	    ctx->msg_src_ip6[3] == bpf_htonl(0)) {