[net-next v2 2/2] bpf: Add eBPF seccomp sample programs

[Sargun Dhillon <sargun-GaZTRHToo+CzQB+pC5nmwQ@public.gmane.org>]

This adds a sample program that uses seccomp-eBPF, called
seccomp1. It shows the simple ability to code seccomp filters
in C.

Signed-off-by: Sargun Dhillon <sargun-GaZTRHToo+CzQB+pC5nmwQ@public.gmane.org>
---
 samples/bpf/Makefile        |  5 +++++
 samples/bpf/bpf_load.c      |  9 +++++++--
 samples/bpf/seccomp1_kern.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 samples/bpf/seccomp1_user.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 100 insertions(+), 2 deletions(-)
 create mode 100644 samples/bpf/seccomp1_kern.c
 create mode 100644 samples/bpf/seccomp1_user.c

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index ec3fc8d88e87..264838846f71 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -43,6 +43,7 @@ hostprogs-y += xdp_redirect_cpu
 hostprogs-y += xdp_monitor
 hostprogs-y += xdp_rxq_info
 hostprogs-y += syscall_tp
+hostprogs-y += seccomp1
 
 # Libbpf dependencies
 LIBBPF := ../../tools/lib/bpf/bpf.o ../../tools/lib/bpf/nlattr.o
@@ -93,6 +94,8 @@ xdp_redirect_cpu-objs := bpf_load.o $(LIBBPF) xdp_redirect_cpu_user.o
 xdp_monitor-objs := bpf_load.o $(LIBBPF) xdp_monitor_user.o
 xdp_rxq_info-objs := bpf_load.o $(LIBBPF) xdp_rxq_info_user.o
 syscall_tp-objs := bpf_load.o $(LIBBPF) syscall_tp_user.o
+seccomp1-objs := bpf_load.o $(LIBBPF) seccomp1_user.o
+
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
@@ -144,6 +147,7 @@ always += xdp_monitor_kern.o
 always += xdp_rxq_info_kern.o
 always += xdp2skb_meta_kern.o
 always += syscall_tp_kern.o
+always += seccomp1_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
 HOSTCFLAGS += -I$(srctree)/tools/lib/
@@ -188,6 +192,7 @@ HOSTLOADLIBES_xdp_redirect_cpu += -lelf
 HOSTLOADLIBES_xdp_monitor += -lelf
 HOSTLOADLIBES_xdp_rxq_info += -lelf
 HOSTLOADLIBES_syscall_tp += -lelf
+HOSTLOADLIBES_seccomp1 += -lelf
 
 # Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
 #  make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
index 69806d74fa53..856bc8b93916 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -67,6 +67,7 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
 	bool is_cgroup_sk = strncmp(event, "cgroup/sock", 11) == 0;
 	bool is_sockops = strncmp(event, "sockops", 7) == 0;
 	bool is_sk_skb = strncmp(event, "sk_skb", 6) == 0;
+	bool is_seccomp = strncmp(event, "seccomp", 7) == 0;
 	size_t insns_cnt = size / sizeof(struct bpf_insn);
 	enum bpf_prog_type prog_type;
 	char buf[256];
@@ -96,6 +97,8 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
 		prog_type = BPF_PROG_TYPE_SOCK_OPS;
 	} else if (is_sk_skb) {
 		prog_type = BPF_PROG_TYPE_SK_SKB;
+	} else if (is_seccomp) {
+		prog_type = BPF_PROG_TYPE_SECCOMP;
 	} else {
 		printf("Unknown event '%s'\n", event);
 		return -1;
@@ -110,7 +113,8 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
 
 	prog_fd[prog_cnt++] = fd;
 
-	if (is_xdp || is_perf_event || is_cgroup_skb || is_cgroup_sk)
+	if (is_xdp || is_perf_event || is_cgroup_skb || is_cgroup_sk ||
+	    is_seccomp)
 		return 0;
 
 	if (is_socket || is_sockops || is_sk_skb) {
@@ -589,7 +593,8 @@ static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map)
 		    memcmp(shname, "socket", 6) == 0 ||
 		    memcmp(shname, "cgroup/", 7) == 0 ||
 		    memcmp(shname, "sockops", 7) == 0 ||
-		    memcmp(shname, "sk_skb", 6) == 0) {
+		    memcmp(shname, "sk_skb", 6) == 0 ||
+		    memcmp(shname, "seccomp", 7) == 0) {
 			ret = load_and_attach(shname, data->d_buf,
 					      data->d_size);
 			if (ret != 0)
diff --git a/samples/bpf/seccomp1_kern.c b/samples/bpf/seccomp1_kern.c
new file mode 100644
index 000000000000..420e37eebd92
--- /dev/null
+++ b/samples/bpf/seccomp1_kern.c
@@ -0,0 +1,43 @@
+#include <uapi/linux/seccomp.h>
+#include <uapi/linux/bpf.h>
+#include <uapi/linux/unistd.h>
+#include "bpf_helpers.h"
+#include <uapi/linux/errno.h>
+#include <uapi/linux/audit.h>
+
+#if defined(__x86_64__)
+#define ARCH	AUDIT_ARCH_X86_64
+#elif defined(__i386__)
+#define ARCH	AUDIT_ARCH_I386
+#else
+#endif
+
+#ifdef ARCH
+/* Returns EPERM when trying to close fd 999 */
+SEC("seccomp")
+int bpf_prog1(struct seccomp_data *ctx)
+{
+	/*
+	 * Make sure this BPF program is being run on the same architecture it
+	 * was compiled on.
+	 */
+	if (ctx->arch != ARCH)
+		return SECCOMP_RET_ERRNO | EPERM;
+	if (ctx->nr == __NR_close && ctx->args[0] == 999)
+		return SECCOMP_RET_ERRNO | EPERM;
+
+	return SECCOMP_RET_ALLOW;
+}
+#else
+#warning Architecture not supported -- Blocking all syscalls
+SEC("seccomp")
+int bpf_prog1(struct seccomp_data *ctx)
+{
+	return SECCOMP_RET_ERRNO | EPERM;
+}
+#endif
+
+
+
+
+char _license[] SEC("license") = "GPL";
diff --git a/samples/bpf/seccomp1_user.c b/samples/bpf/seccomp1_user.c
new file mode 100644
index 000000000000..b4951e0ca56f
--- /dev/null
+++ b/samples/bpf/seccomp1_user.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <assert.h>
+#include <stdio.h>
+#include <linux/bpf.h>
+#include <unistd.h>
+#include "libbpf.h"
+#include "bpf_load.h"
+#include <linux/bpf.h>
+#include <sys/prctl.h>
+#include <strings.h>
+#include <errno.h>
+#include <linux/unistd.h>
+#include <linux/seccomp.h>
+
+int main(int argc, char **argv)
+{
+	char filename[256];
+
+
+	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+	if (load_bpf_file(filename)) {
+		printf("%s", bpf_log_buf);
+		return 1;
+	}
+
+	/* set new_new_privs so non-privileged users can attach filters */
+	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+		perror("prctl(NO_NEW_PRIVS)");
+		return 1;
+	}
+
+	if (syscall(__NR_seccomp, SECCOMP_SET_MODE_FILTER,
+		    SECCOMP_FILTER_FLAG_EXTENDED, &prog_fd)) {
+		perror("seccomp");
+		return 1;
+	}
+
+	close(111);
+	assert(errno == EBADF);
+	close(999);
+	assert(errno = EPERM);
+
+	return 0;
+}
-- 
2.14.1