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Thu, 02 Apr 2026 20:38:47 -0700 (PDT) From: Qi Tang To: Alexei Starovoitov , Daniel Borkmann Cc: Kumar Kartikeya Dwivedi , Eduard Zingerman , Andrii Nakryiko , Martin KaFai Lau , John Fastabend , Song Liu , bpf@vger.kernel.org, Qi Tang Subject: [PATCH bpf v4 2/2] selftests/bpf: add test for nullable PTR_TO_BUF access Date: Fri, 3 Apr 2026 11:38:28 +0800 Message-ID: <20260403033828.18529-3-tpluszz77@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260403033828.18529-1-tpluszz77@gmail.com> References: <20260403033828.18529-1-tpluszz77@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 iter_buf_null_fail with two tests and a test runner: - iter_buf_null_deref: verifier must reject direct dereference of ctx->key (PTR_TO_BUF | PTR_MAYBE_NULL) without a null check - iter_buf_null_check_ok: verifier must accept dereference after an explicit null check Signed-off-by: Qi Tang --- .../bpf/prog_tests/iter_buf_null_fail.c | 9 ++++ .../selftests/bpf/progs/iter_buf_null_fail.c | 51 +++++++++++++++++++ 2 files changed, 60 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/iter_buf_null_fail.c create mode 100644 tools/testing/selftests/bpf/progs/iter_buf_null_fail.c diff --git a/tools/testing/selftests/bpf/prog_tests/iter_buf_null_fail.c b/tools/testing/selftests/bpf/prog_tests/iter_buf_null_fail.c new file mode 100644 index 000000000000..ea97787b870d --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/iter_buf_null_fail.c @@ -0,0 +1,9 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include "iter_buf_null_fail.skel.h" + +void test_iter_buf_null_fail(void) +{ + RUN_TESTS(iter_buf_null_fail); +} diff --git a/tools/testing/selftests/bpf/progs/iter_buf_null_fail.c b/tools/testing/selftests/bpf/progs/iter_buf_null_fail.c new file mode 100644 index 000000000000..963a4cfc33f3 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/iter_buf_null_fail.c @@ -0,0 +1,51 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Qi Tang */ + +#include +#include +#include "bpf_misc.h" + +char _license[] SEC("license") = "GPL"; + +struct { + __uint(type, BPF_MAP_TYPE_HASH); + __uint(max_entries, 1); + __type(key, __u32); + __type(value, __u64); +} hashmap SEC(".maps"); + +/* + * Verify that the verifier rejects direct access to nullable PTR_TO_BUF + * (ctx->key) without a null check. On the iterator stop callback, + * ctx->key is NULL, so unconditional access would be a NULL deref. + */ +SEC("iter/bpf_map_elem") +__failure __msg("invalid mem access") +int iter_buf_null_deref(struct bpf_iter__bpf_map_elem *ctx) +{ + /* ctx->key is PTR_TO_BUF | PTR_MAYBE_NULL | MEM_RDONLY. + * Direct access without null check must be rejected. + */ + volatile __u32 v = *(__u32 *)ctx->key; + + (void)v; + return 0; +} + +/* + * Verify that access after a null check is still accepted. + */ +SEC("iter/bpf_map_elem") +__success +int iter_buf_null_check_ok(struct bpf_iter__bpf_map_elem *ctx) +{ + __u32 *key = ctx->key; + + if (!key) + return 0; + + volatile __u32 v = *key; + + (void)v; + return 0; +} -- 2.43.0