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selftests/bpf: Add tests for _opts variants of bpf_*_get_fd_by_id()

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Introduce the data_input map, write-protected with a small eBPF program
implementing the lsm/bpf_map hook.

Then, ensure that bpf_map_get_fd_by_id() and bpf_map_get_fd_by_id_opts()
with NULL opts don't succeed due to requesting read-write access to the
write-protected map. Also, ensure that bpf_map_get_fd_by_id_opts() with
open_flags in opts set to BPF_F_RDONLY instead succeeds.

After obtaining a read-only fd, ensure that only map lookup succeeds and
not update. Ensure that update works only with the read-write fd obtained
at program loading time, when the write protection was not yet enabled.

Finally, ensure that the other _opts variants of bpf_*_get_fd_by_id() don't
work if the BPF_F_RDONLY flag is set in opts (due to the kernel not
handling the open_flags member of bpf_attr).

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20221006110736.84253-7-roberto.sassu@huaweicloud.com
This commit is contained in:
Roberto Sassu 2022-10-06 13:07:36 +02:00 committed by Andrii Nakryiko
parent 97c8f9dd5d
commit a9c7c18b57
3 changed files with 124 additions and 0 deletions
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1
tools/testing/selftests/bpf/DENYLIST.s390x
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@ -76,3 +76,4 @@ lookup_key # JIT does not support calling kernel f
verify_pkcs7_sig # JIT does not support calling kernel function (kfunc)
kfunc_dynptr_param # JIT does not support calling kernel function (kfunc)
deny_namespace # failed to attach: ERROR: strerror_r(-524)=22 (trampoline)
libbpf_get_fd_by_id_opts # failed to attach: ERROR: strerror_r(-524)=22 (trampoline)

87
tools/testing/selftests/bpf/prog_tests/libbpf_get_fd_by_id_opts.c Normal file
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@ -0,0 +1,87 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2022 Huawei Technologies Duesseldorf GmbH
*
* Author: Roberto Sassu <roberto.sassu@huawei.com>
*/
#include <test_progs.h>
#include "test_libbpf_get_fd_by_id_opts.skel.h"
void test_libbpf_get_fd_by_id_opts(void)
{
struct test_libbpf_get_fd_by_id_opts *skel;
struct bpf_map_info info_m = {};
__u32 len = sizeof(info_m), value;
int ret, zero = 0, fd = -1;
LIBBPF_OPTS(bpf_get_fd_by_id_opts, fd_opts_rdonly,
.open_flags = BPF_F_RDONLY,
);
skel = test_libbpf_get_fd_by_id_opts__open_and_load();
if (!ASSERT_OK_PTR(skel,
"test_libbpf_get_fd_by_id_opts__open_and_load"))
return;
ret = test_libbpf_get_fd_by_id_opts__attach(skel);
if (!ASSERT_OK(ret, "test_libbpf_get_fd_by_id_opts__attach"))
goto close_prog;
ret = bpf_obj_get_info_by_fd(bpf_map__fd(skel->maps.data_input),
&info_m, &len);
if (!ASSERT_OK(ret, "bpf_obj_get_info_by_fd"))
goto close_prog;
fd = bpf_map_get_fd_by_id(info_m.id);
if (!ASSERT_LT(fd, 0, "bpf_map_get_fd_by_id"))
goto close_prog;
fd = bpf_map_get_fd_by_id_opts(info_m.id, NULL);
if (!ASSERT_LT(fd, 0, "bpf_map_get_fd_by_id_opts"))
goto close_prog;
fd = bpf_map_get_fd_by_id_opts(info_m.id, &fd_opts_rdonly);
if (!ASSERT_GE(fd, 0, "bpf_map_get_fd_by_id_opts"))
goto close_prog;
/* Map lookup should work with read-only fd. */
ret = bpf_map_lookup_elem(fd, &zero, &value);
if (!ASSERT_OK(ret, "bpf_map_lookup_elem"))
goto close_prog;
if (!ASSERT_EQ(value, 0, "map value mismatch"))
goto close_prog;
/* Map update should not work with read-only fd. */
ret = bpf_map_update_elem(fd, &zero, &len, BPF_ANY);
if (!ASSERT_LT(ret, 0, "bpf_map_update_elem"))
goto close_prog;
/* Map update should work with read-write fd. */
ret = bpf_map_update_elem(bpf_map__fd(skel->maps.data_input), &zero,
&len, BPF_ANY);
if (!ASSERT_OK(ret, "bpf_map_update_elem"))
goto close_prog;
/* Prog get fd with opts set should not work (no kernel support). */
ret = bpf_prog_get_fd_by_id_opts(0, &fd_opts_rdonly);
if (!ASSERT_EQ(ret, -EINVAL, "bpf_prog_get_fd_by_id_opts"))
goto close_prog;
/* Link get fd with opts set should not work (no kernel support). */
ret = bpf_link_get_fd_by_id_opts(0, &fd_opts_rdonly);
if (!ASSERT_EQ(ret, -EINVAL, "bpf_link_get_fd_by_id_opts"))
goto close_prog;
/* BTF get fd with opts set should not work (no kernel support). */
ret = bpf_btf_get_fd_by_id_opts(0, &fd_opts_rdonly);
ASSERT_EQ(ret, -EINVAL, "bpf_btf_get_fd_by_id_opts");
close_prog:
if (fd >= 0)
close(fd);
test_libbpf_get_fd_by_id_opts__destroy(skel);
}

36
tools/testing/selftests/bpf/progs/test_libbpf_get_fd_by_id_opts.c Normal file
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@ -0,0 +1,36 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2022 Huawei Technologies Duesseldorf GmbH
*
* Author: Roberto Sassu <roberto.sassu@huawei.com>
*/
#include "vmlinux.h"
#include <errno.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
/* From include/linux/mm.h. */
#define FMODE_WRITE 0x2
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, 1);
__type(key, __u32);
__type(value, __u32);
} data_input SEC(".maps");
char _license[] SEC("license") = "GPL";
SEC("lsm/bpf_map")
int BPF_PROG(check_access, struct bpf_map *map, fmode_t fmode)
{
if (map != (struct bpf_map *)&data_input)
return 0;
if (fmode & FMODE_WRITE)
return -EACCES;
return 0;
}