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Sat, 04 Apr 2026 09:12:56 -0700 (PDT) From: Weiming Shi To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi Cc: Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , bpf@vger.kernel.org, Xiang Mei , Weiming Shi Subject: [PATCH bpf v3 2/2] selftests/bpf: add test for negative CO-RE accessor index rejection Date: Sun, 5 Apr 2026 00:12:21 +0800 Message-ID: <20260404161221.961828-3-bestswngs@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260404161221.961828-1-bestswngs@gmail.com> References: <20260404161221.961828-1-bestswngs@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add a selftest to verify that the kernel rejects BPF programs containing CO-RE relocations with negative accessor indices. The test constructs a minimal BTF blob with a struct type and a CO-RE relocation whose access string is "0:-1". Without the fix in the previous patch, this triggers an out-of-bounds read in bpf_core_parse_spec(); with the fix, the program load fails cleanly with -EINVAL. Signed-off-by: Weiming Shi --- .../selftests/bpf/prog_tests/core_reloc_raw.c | 94 +++++++++++++++++++ 1 file changed, 94 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c b/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c index a18d3680fb16..f7bf6c237d59 100644 --- a/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c +++ b/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c @@ -118,8 +118,102 @@ static void test_bad_local_id(void) close(btf_fd); } +/* Check that verifier rejects BPF program containing CO-RE relocation + * with a negative accessor index (e.g. "0:-1"). + */ +static void test_negative_accessor(void) +{ + struct test_btf { + struct btf_header hdr; + __u32 types[18]; + char strings[20]; + } raw_btf = { + .hdr = { + .magic = BTF_MAGIC, + .version = BTF_VERSION, + .hdr_len = sizeof(struct btf_header), + .type_off = 0, + .type_len = sizeof(raw_btf.types), + .str_off = offsetof(struct test_btf, strings) - + offsetof(struct test_btf, types), + .str_len = sizeof(raw_btf.strings), + }, + .types = { + /* [1] int */ + BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4), + /* [2] struct s { int x; } */ + BTF_STRUCT_ENC(5, 1, 4), + BTF_MEMBER_ENC(7, 1, 0), + /* [3] int (*)(int a) */ + BTF_FUNC_PROTO_ENC(1, 1), + BTF_FUNC_PROTO_ARG_ENC(13, 1), + /* [4] FUNC 'foo' */ + BTF_FUNC_ENC(9, 3), + }, + /* offsets: 0:NUL 1:"int" 5:"s" 7:"x" 9:"foo" 13:"a" 15:"0:-1" */ + .strings = "\0int\0s\0x\0foo\0a\0" "0:-1", + }; + __u32 log_level = 1 | 2 | 4; + LIBBPF_OPTS(bpf_btf_load_opts, opts, + .log_buf = log, + .log_size = sizeof(log), + .log_level = log_level, + ); + struct bpf_insn insns[] = { + BPF_ALU64_IMM(BPF_MOV, BPF_REG_0, 0), + BPF_EXIT_INSN(), + }; + struct bpf_func_info funcs[] = { + { .insn_off = 0, .type_id = 4 } + }; + struct bpf_core_relo relos[] = { + { + .insn_off = 0, + .type_id = 2, /* struct s */ + .access_str_off = 15, /* "0:-1" */ + .kind = BPF_CORE_FIELD_BYTE_OFFSET, + } + }; + union bpf_attr attr; + int prog_fd = -1; + int btf_fd = -1; + + btf_fd = bpf_btf_load(&raw_btf, sizeof(raw_btf), &opts); + if (!ASSERT_GE(btf_fd, 0, "btf_load")) + return; + + log[0] = 0; + memset(&attr, 0, sizeof(attr)); + attr.prog_btf_fd = btf_fd; + attr.prog_type = BPF_TRACE_RAW_TP; + attr.license = (__u64)"GPL"; + attr.insns = (__u64)&insns; + attr.insn_cnt = sizeof(insns) / sizeof(*insns); + attr.log_buf = (__u64)log; + attr.log_size = sizeof(log); + attr.log_level = log_level; + attr.func_info = (__u64)funcs; + attr.func_info_cnt = sizeof(funcs) / sizeof(*funcs); + attr.func_info_rec_size = sizeof(*funcs); + attr.core_relos = (__u64)relos; + attr.core_relo_cnt = sizeof(relos) / sizeof(*relos); + attr.core_relo_rec_size = sizeof(*relos); + prog_fd = sys_bpf_prog_load(&attr, sizeof(attr), 1); + if (prog_fd >= 0) { + PRINT_FAIL("sys_bpf_prog_load() expected to fail\n"); + goto out; + } + ASSERT_HAS_SUBSTR(log, "failed: -22", "prog_load_log"); + +out: + close(prog_fd); + close(btf_fd); +} + void test_core_reloc_raw(void) { if (test__start_subtest("bad_local_id")) test_bad_local_id(); + if (test__start_subtest("negative_accessor")) + test_negative_accessor(); } -- 2.43.0