Extend the snprintf_btf test with type_ids from the vmlinux BTF that used to NULL-deref in the BTF show path: a "const void", checked to render the "<unsupported kind:0>" placeholder, and a BTF_KIND_VAR, checked to resolve and render without error.
The program renders from its own buffer and the test picks a VAR whose resolved type fits it, so the render stays in bounds. Signed-off-by: Jiayuan Chen <[email protected]> --- .../selftests/bpf/prog_tests/snprintf_btf.c | 79 +++++++++++++++++++ .../selftests/bpf/progs/snprintf_btf_void.c | 24 ++++++ 2 files changed, 103 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/snprintf_btf_void.c diff --git a/tools/testing/selftests/bpf/prog_tests/snprintf_btf.c b/tools/testing/selftests/bpf/prog_tests/snprintf_btf.c index dd41b826be30..edce9c1b54fb 100644 --- a/tools/testing/selftests/bpf/prog_tests/snprintf_btf.c +++ b/tools/testing/selftests/bpf/prog_tests/snprintf_btf.c @@ -1,7 +1,9 @@ // SPDX-License-Identifier: GPL-2.0 #include <test_progs.h> #include <linux/btf.h> +#include <bpf/btf.h> #include "netif_receive_skb.skel.h" +#include "snprintf_btf_void.skel.h" /* Demonstrate that bpf_snprintf_btf succeeds and that various data types * are formatted correctly. @@ -58,3 +60,80 @@ void serial_test_snprintf_btf(void) cleanup: netif_receive_skb__destroy(skel); } + +/* + * bpf_snprintf_btf() renders a type_id taken straight from the vmlinux BTF. + * Two such type_ids used to NULL-deref in the BTF show path: + * - a "const void" (a modifier resolving to void) in btf_modifier_show() + * - a BTF_KIND_VAR in btf_var_show() (base BTF has no resolved_ids) + * A fixed kernel renders both without crashing. + */ +static long run(struct snprintf_btf_void *skel, __u32 type_id) +{ + LIBBPF_OPTS(bpf_test_run_opts, topts); + char ctx[8] = {}; + + skel->bss->type_id = type_id; + topts.ctx_in = ctx; + topts.ctx_size_in = sizeof(ctx); + if (!ASSERT_OK(bpf_prog_test_run_opts(bpf_program__fd(skel->progs.dump_type), + &topts), "test_run")) + return -1; + return skel->bss->ret; +} + +void test_snprintf_btf_void(void) +{ + const struct btf_type *t; + struct snprintf_btf_void *skel; + int i, n, cv = 0, var = 0; + struct btf *btf; + + btf = btf__parse("/sys/kernel/btf/vmlinux", NULL); + if (!btf) { + test__skip(); + return; + } + + skel = snprintf_btf_void__open_and_load(); + if (!ASSERT_OK_PTR(skel, "skel_open_and_load")) + goto out_btf; + + n = btf__type_cnt(btf); + for (i = 1; i < n && !(cv && var); i++) { + t = btf__type_by_id(btf, i); + if (!cv && btf_kind(t) == BTF_KIND_CONST && t->type == 0) + cv = i; + /* Pick a VAR small enough to render from the program's buffer. */ + if (!var && btf_kind(t) == BTF_KIND_VAR) { + long sz = btf__resolve_size(btf, t->type); + + if (sz > 0 && sz <= (long)sizeof(skel->bss->obj)) + var = i; + } + } + + /* "const void" renders the "<unsupported kind:0>" placeholder. */ + if (test__start_subtest("const_void")) { + if (cv) { + ASSERT_EQ(run(skel, cv), + sizeof("<unsupported kind:0>") - 1, "ret"); + ASSERT_STREQ(skel->bss->out, "<unsupported kind:0>", + "placeholder"); + } else { + test__skip(); + } + } + + /* A BTF_KIND_VAR must resolve and render without error. */ + if (test__start_subtest("var")) { + if (var) + ASSERT_GT(run(skel, var), 0, "ret"); + else + test__skip(); + } + + snprintf_btf_void__destroy(skel); +out_btf: + btf__free(btf); +} diff --git a/tools/testing/selftests/bpf/progs/snprintf_btf_void.c b/tools/testing/selftests/bpf/progs/snprintf_btf_void.c new file mode 100644 index 000000000000..44af80fbbb80 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/snprintf_btf_void.c @@ -0,0 +1,24 @@ +// SPDX-License-Identifier: GPL-2.0 +#include "btf_ptr.h" +#include <bpf/bpf_helpers.h> + +__u32 type_id; +/* A buffer we own to render the selected type from, kept in bounds. */ +char obj[256]; +char out[64]; +long ret; + +SEC("raw_tp/sys_enter") +int dump_type(void *ctx) +{ + struct btf_ptr ptr = { + .ptr = obj, + .type_id = type_id, + .flags = 0, + }; + + ret = bpf_snprintf_btf(out, sizeof(out), &ptr, sizeof(ptr), 0); + return 0; +} + +char _license[] SEC("license") = "GPL"; -- 2.43.0
