Merge branch 'bpf: refine kernel.unprivileged_bpf_disabled behaviour'

Alan Maguire says:

====================

Unprivileged BPF disabled (kernel.unprivileged_bpf_disabled >= 1)
is the default in most cases now; when set, the BPF system call is
blocked for users without CAP_BPF/CAP_SYS_ADMIN.  In some cases
however, it makes sense to split activities between capability-requiring
ones - such as program load/attach - and those that might not require
capabilities such as reading perf/ringbuf events, reading or
updating BPF map configuration etc.  One example of this sort of
approach is a service that loads a BPF program, and a user-space
program that interacts with it.

Here - rather than blocking all BPF syscall commands - unprivileged
BPF disabled blocks the key object-creating commands (prog load,
map load).  Discussion has alluded to this idea in the past [1],
and Alexei mentioned it was also discussed at LSF/MM/BPF this year.

Changes since v3 [2]:
- added acks to patch 1
- CI was failing on Ubuntu; I suspect the issue was an old capability.h
  file which specified CAP_LAST_CAP as < CAP_BPF, leading to the logic
  disabling all caps not disabling CAP_BPF.  Use CAP_BPF as basis for
  "all caps" bitmap instead as we explicitly define it in cap_helpers.h
  if not already found in capabilities.h
- made global variables arguments to subtests instead (Andrii, patch 2)

Changes since v2 [3]:

- added acks from Yonghong
- clang compilation issue in selftest with bpf_prog_query()
  (Alexei, patch 2)
- disable all capabilities for test (Yonghong, patch 2)
- add assertions that size of perf/ringbuf data matches expectations
  (Yonghong, patch 2)
- add map array size definition, remove unneeded whitespace (Yonghong, patch 2)

Changes since RFC [4]:

- widened scope of commands unprivileged BPF disabled allows
  (Alexei, patch 1)
- removed restrictions on map types for lookup, update, delete
  (Alexei, patch 1)
- removed kernel CONFIG parameter controlling unprivileged bpf disabled
  change (Alexei, patch 1)
- widened test scope to cover most BPF syscall commands, with positive
  and negative subtests

[1] https://lore.kernel.org/bpf/CAADnVQLTBhCTAx1a_nev7CgMZxv1Bb7ecz1AFRin8tHmjPREJA@mail.gmail.com/
[2] https://lore.kernel.org/bpf/1652880861-27373-1-git-send-email-alan.maguire@oracle.com/T/
[3] https://lore.kernel.org/bpf/1652788780-25520-1-git-send-email-alan.maguire@oracle.com/T/#t
[4] https://lore.kernel.org/bpf/20220511163604.5kuczj6jx3ec5qv6@MBP-98dd607d3435.dhcp.thefacebook.com/T/#mae65f35a193279e718f37686da636094d69b96ee
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/syscall.c

@@ -4863,9 +4863,21 @@ static int bpf_prog_bind_map(union bpf_attr *attr)
 static int __sys_bpf(int cmd, bpfptr_t uattr, unsigned int size)
 {
 	union bpf_attr attr;
+	bool capable;
 	int err;
 
-	if (sysctl_unprivileged_bpf_disabled && !bpf_capable())
+	capable = bpf_capable() || !sysctl_unprivileged_bpf_disabled;
+
+	/* Intent here is for unprivileged_bpf_disabled to block key object
+	 * creation commands for unprivileged users; other actions depend
+	 * of fd availability and access to bpffs, so are dependent on
+	 * object creation success.  Capabilities are later verified for
+	 * operations such as load and map create, so even with unprivileged
+	 * BPF disabled, capability checks are still carried out for these
+	 * and other operations.
+	 */
+	if (!capable &&
+	    (cmd == BPF_MAP_CREATE || cmd == BPF_PROG_LOAD))
 		return -EPERM;
 
 	err = bpf_check_uarg_tail_zero(uattr, sizeof(attr), size);

tools/testing/selftests/bpf/prog_tests/unpriv_bpf_disabled.c

@@ -0,0 +1,312 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022, Oracle and/or its affiliates. */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+
+#include "test_unpriv_bpf_disabled.skel.h"
+
+#include "cap_helpers.h"
+
+/* Using CAP_LAST_CAP is risky here, since it can get pulled in from
+ * an old /usr/include/linux/capability.h and be < CAP_BPF; as a result
+ * CAP_BPF would not be included in ALL_CAPS.  Instead use CAP_BPF as
+ * we know its value is correct since it is explicitly defined in
+ * cap_helpers.h.
+ */
+#define ALL_CAPS	((2ULL << CAP_BPF) - 1)
+
+#define PINPATH		"/sys/fs/bpf/unpriv_bpf_disabled_"
+#define NUM_MAPS	7
+
+static __u32 got_perfbuf_val;
+static __u32 got_ringbuf_val;
+
+static int process_ringbuf(void *ctx, void *data, size_t len)
+{
+	if (ASSERT_EQ(len, sizeof(__u32), "ringbuf_size_valid"))
+		got_ringbuf_val = *(__u32 *)data;
+	return 0;
+}
+
+static void process_perfbuf(void *ctx, int cpu, void *data, __u32 len)
+{
+	if (ASSERT_EQ(len, sizeof(__u32), "perfbuf_size_valid"))
+		got_perfbuf_val = *(__u32 *)data;
+}
+
+static int sysctl_set(const char *sysctl_path, char *old_val, const char *new_val)
+{
+	int ret = 0;
+	FILE *fp;
+
+	fp = fopen(sysctl_path, "r+");
+	if (!fp)
+		return -errno;
+	if (old_val && fscanf(fp, "%s", old_val) <= 0) {
+		ret = -ENOENT;
+	} else if (!old_val || strcmp(old_val, new_val) != 0) {
+		fseek(fp, 0, SEEK_SET);
+		if (fprintf(fp, "%s", new_val) < 0)
+			ret = -errno;
+	}
+	fclose(fp);
+
+	return ret;
+}
+
+static void test_unpriv_bpf_disabled_positive(struct test_unpriv_bpf_disabled *skel,
+					      __u32 prog_id, int prog_fd, int perf_fd,
+					      char **map_paths, int *map_fds)
+{
+	struct perf_buffer *perfbuf = NULL;
+	struct ring_buffer *ringbuf = NULL;
+	int i, nr_cpus, link_fd = -1;
+
+	nr_cpus = bpf_num_possible_cpus();
+
+	skel->bss->perfbuf_val = 1;
+	skel->bss->ringbuf_val = 2;
+
+	/* Positive tests for unprivileged BPF disabled. Verify we can
+	 * - retrieve and interact with pinned maps;
+	 * - set up and interact with perf buffer;
+	 * - set up and interact with ring buffer;
+	 * - create a link
+	 */
+	perfbuf = perf_buffer__new(bpf_map__fd(skel->maps.perfbuf), 8, process_perfbuf, NULL, NULL,
+				   NULL);
+	if (!ASSERT_OK_PTR(perfbuf, "perf_buffer__new"))
+		goto cleanup;
+
+	ringbuf = ring_buffer__new(bpf_map__fd(skel->maps.ringbuf), process_ringbuf, NULL, NULL);
+	if (!ASSERT_OK_PTR(ringbuf, "ring_buffer__new"))
+		goto cleanup;
+
+	/* trigger & validate perf event, ringbuf output */
+	usleep(1);
+
+	ASSERT_GT(perf_buffer__poll(perfbuf, 100), -1, "perf_buffer__poll");
+	ASSERT_EQ(got_perfbuf_val, skel->bss->perfbuf_val, "check_perfbuf_val");
+	ASSERT_EQ(ring_buffer__consume(ringbuf), 1, "ring_buffer__consume");
+	ASSERT_EQ(got_ringbuf_val, skel->bss->ringbuf_val, "check_ringbuf_val");
+
+	for (i = 0; i < NUM_MAPS; i++) {
+		map_fds[i] = bpf_obj_get(map_paths[i]);
+		if (!ASSERT_GT(map_fds[i], -1, "obj_get"))
+			goto cleanup;
+	}
+
+	for (i = 0; i < NUM_MAPS; i++) {
+		bool prog_array = strstr(map_paths[i], "prog_array") != NULL;
+		bool array = strstr(map_paths[i], "array") != NULL;
+		bool buf = strstr(map_paths[i], "buf") != NULL;
+		__u32 key = 0, vals[nr_cpus], lookup_vals[nr_cpus];
+		__u32 expected_val = 1;
+		int j;
+
+		/* skip ringbuf, perfbuf */
+		if (buf)
+			continue;
+
+		for (j = 0; j < nr_cpus; j++)
+			vals[j] = expected_val;
+
+		if (prog_array) {
+			/* need valid prog array value */
+			vals[0] = prog_fd;
+			/* prog array lookup returns prog id, not fd */
+			expected_val = prog_id;
+		}
+		ASSERT_OK(bpf_map_update_elem(map_fds[i], &key, vals, 0), "map_update_elem");
+		ASSERT_OK(bpf_map_lookup_elem(map_fds[i], &key, &lookup_vals), "map_lookup_elem");
+		ASSERT_EQ(lookup_vals[0], expected_val, "map_lookup_elem_values");
+		if (!array)
+			ASSERT_OK(bpf_map_delete_elem(map_fds[i], &key), "map_delete_elem");
+	}
+
+	link_fd = bpf_link_create(bpf_program__fd(skel->progs.handle_perf_event), perf_fd,
+				  BPF_PERF_EVENT, NULL);
+	ASSERT_GT(link_fd, 0, "link_create");
+
+cleanup:
+	if (link_fd)
+		close(link_fd);
+	if (perfbuf)
+		perf_buffer__free(perfbuf);
+	if (ringbuf)
+		ring_buffer__free(ringbuf);
+}
+
+static void test_unpriv_bpf_disabled_negative(struct test_unpriv_bpf_disabled *skel,
+					      __u32 prog_id, int prog_fd, int perf_fd,
+					      char **map_paths, int *map_fds)
+{
+	const struct bpf_insn prog_insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	const size_t prog_insn_cnt = sizeof(prog_insns) / sizeof(struct bpf_insn);
+	LIBBPF_OPTS(bpf_prog_load_opts, load_opts);
+	struct bpf_map_info map_info = {};
+	__u32 map_info_len = sizeof(map_info);
+	struct bpf_link_info link_info = {};
+	__u32 link_info_len = sizeof(link_info);
+	struct btf *btf = NULL;
+	__u32 attach_flags = 0;
+	__u32 prog_ids[3] = {};
+	__u32 prog_cnt = 3;
+	__u32 next;
+	int i;
+
+	/* Negative tests for unprivileged BPF disabled.  Verify we cannot
+	 * - load BPF programs;
+	 * - create BPF maps;
+	 * - get a prog/map/link fd by id;
+	 * - get next prog/map/link id
+	 * - query prog
+	 * - BTF load
+	 */
+	ASSERT_EQ(bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "simple_prog", "GPL",
+				prog_insns, prog_insn_cnt, &load_opts),
+		  -EPERM, "prog_load_fails");
+
+	for (i = BPF_MAP_TYPE_HASH; i <= BPF_MAP_TYPE_BLOOM_FILTER; i++)
+		ASSERT_EQ(bpf_map_create(i, NULL, sizeof(int), sizeof(int), 1, NULL),
+			  -EPERM, "map_create_fails");
+
+	ASSERT_EQ(bpf_prog_get_fd_by_id(prog_id), -EPERM, "prog_get_fd_by_id_fails");
+	ASSERT_EQ(bpf_prog_get_next_id(prog_id, &next), -EPERM, "prog_get_next_id_fails");
+	ASSERT_EQ(bpf_prog_get_next_id(0, &next), -EPERM, "prog_get_next_id_fails");
+
+	if (ASSERT_OK(bpf_obj_get_info_by_fd(map_fds[0], &map_info, &map_info_len),
+		      "obj_get_info_by_fd")) {
+		ASSERT_EQ(bpf_map_get_fd_by_id(map_info.id), -EPERM, "map_get_fd_by_id_fails");
+		ASSERT_EQ(bpf_map_get_next_id(map_info.id, &next), -EPERM,
+			  "map_get_next_id_fails");
+	}
+	ASSERT_EQ(bpf_map_get_next_id(0, &next), -EPERM, "map_get_next_id_fails");
+
+	if (ASSERT_OK(bpf_obj_get_info_by_fd(bpf_link__fd(skel->links.sys_nanosleep_enter),
+					     &link_info, &link_info_len),
+		      "obj_get_info_by_fd")) {
+		ASSERT_EQ(bpf_link_get_fd_by_id(link_info.id), -EPERM, "link_get_fd_by_id_fails");
+		ASSERT_EQ(bpf_link_get_next_id(link_info.id, &next), -EPERM,
+			  "link_get_next_id_fails");
+	}
+	ASSERT_EQ(bpf_link_get_next_id(0, &next), -EPERM, "link_get_next_id_fails");
+
+	ASSERT_EQ(bpf_prog_query(prog_fd, BPF_TRACE_FENTRY, 0, &attach_flags, prog_ids,
+				 &prog_cnt), -EPERM, "prog_query_fails");
+
+	btf = btf__new_empty();
+	if (ASSERT_OK_PTR(btf, "empty_btf") &&
+	    ASSERT_GT(btf__add_int(btf, "int", 4, 0), 0, "unpriv_int_type")) {
+		const void *raw_btf_data;
+		__u32 raw_btf_size;
+
+		raw_btf_data = btf__raw_data(btf, &raw_btf_size);
+		if (ASSERT_OK_PTR(raw_btf_data, "raw_btf_data_good"))
+			ASSERT_EQ(bpf_btf_load(raw_btf_data, raw_btf_size, NULL), -EPERM,
+				  "bpf_btf_load_fails");
+	}
+	btf__free(btf);
+}
+
+void test_unpriv_bpf_disabled(void)
+{
+	char *map_paths[NUM_MAPS] = {	PINPATH	"array",
+					PINPATH "percpu_array",
+					PINPATH "hash",
+					PINPATH "percpu_hash",
+					PINPATH "perfbuf",
+					PINPATH "ringbuf",
+					PINPATH "prog_array" };
+	int map_fds[NUM_MAPS];
+	struct test_unpriv_bpf_disabled *skel;
+	char unprivileged_bpf_disabled_orig[32] = {};
+	char perf_event_paranoid_orig[32] = {};
+	struct bpf_prog_info prog_info = {};
+	__u32 prog_info_len = sizeof(prog_info);
+	struct perf_event_attr attr = {};
+	int prog_fd, perf_fd = -1, i, ret;
+	__u64 save_caps = 0;
+	__u32 prog_id;
+
+	skel = test_unpriv_bpf_disabled__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	skel->bss->test_pid = getpid();
+
+	map_fds[0] = bpf_map__fd(skel->maps.array);
+	map_fds[1] = bpf_map__fd(skel->maps.percpu_array);
+	map_fds[2] = bpf_map__fd(skel->maps.hash);
+	map_fds[3] = bpf_map__fd(skel->maps.percpu_hash);
+	map_fds[4] = bpf_map__fd(skel->maps.perfbuf);
+	map_fds[5] = bpf_map__fd(skel->maps.ringbuf);
+	map_fds[6] = bpf_map__fd(skel->maps.prog_array);
+
+	for (i = 0; i < NUM_MAPS; i++)
+		ASSERT_OK(bpf_obj_pin(map_fds[i], map_paths[i]), "pin map_fd");
+
+	/* allow user without caps to use perf events */
+	if (!ASSERT_OK(sysctl_set("/proc/sys/kernel/perf_event_paranoid", perf_event_paranoid_orig,
+				  "-1"),
+		       "set_perf_event_paranoid"))
+		goto cleanup;
+	/* ensure unprivileged bpf disabled is set */
+	ret = sysctl_set("/proc/sys/kernel/unprivileged_bpf_disabled",
+			 unprivileged_bpf_disabled_orig, "2");
+	if (ret == -EPERM) {
+		/* if unprivileged_bpf_disabled=1, we get -EPERM back; that's okay. */
+		if (!ASSERT_OK(strcmp(unprivileged_bpf_disabled_orig, "1"),
+			       "unpriviliged_bpf_disabled_on"))
+			goto cleanup;
+	} else {
+		if (!ASSERT_OK(ret, "set unpriviliged_bpf_disabled"))
+			goto cleanup;
+	}
+
+	prog_fd = bpf_program__fd(skel->progs.sys_nanosleep_enter);
+	ASSERT_OK(bpf_obj_get_info_by_fd(prog_fd, &prog_info, &prog_info_len),
+		  "obj_get_info_by_fd");
+	prog_id = prog_info.id;
+	ASSERT_GT(prog_id, 0, "valid_prog_id");
+
+	attr.size = sizeof(attr);
+	attr.type = PERF_TYPE_SOFTWARE;
+	attr.config = PERF_COUNT_SW_CPU_CLOCK;
+	attr.freq = 1;
+	attr.sample_freq = 1000;
+	perf_fd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
+	if (!ASSERT_GE(perf_fd, 0, "perf_fd"))
+		goto cleanup;
+
+	if (!ASSERT_OK(test_unpriv_bpf_disabled__attach(skel), "skel_attach"))
+		goto cleanup;
+
+	if (!ASSERT_OK(cap_disable_effective(ALL_CAPS, &save_caps), "disable caps"))
+		goto cleanup;
+
+	if (test__start_subtest("unpriv_bpf_disabled_positive"))
+		test_unpriv_bpf_disabled_positive(skel, prog_id, prog_fd, perf_fd, map_paths,
+						  map_fds);
+
+	if (test__start_subtest("unpriv_bpf_disabled_negative"))
+		test_unpriv_bpf_disabled_negative(skel, prog_id, prog_fd, perf_fd, map_paths,
+						  map_fds);
+
+cleanup:
+	close(perf_fd);
+	if (save_caps)
+		cap_enable_effective(save_caps, NULL);
+	if (strlen(perf_event_paranoid_orig) > 0)
+		sysctl_set("/proc/sys/kernel/perf_event_paranoid", NULL, perf_event_paranoid_orig);
+	if (strlen(unprivileged_bpf_disabled_orig) > 0)
+		sysctl_set("/proc/sys/kernel/unprivileged_bpf_disabled", NULL,
+			   unprivileged_bpf_disabled_orig);
+	for (i = 0; i < NUM_MAPS; i++)
+		unlink(map_paths[i]);
+	test_unpriv_bpf_disabled__destroy(skel);
+}