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Tue, 11 Aug 2026 07:19:23 -0700 (PDT) From: Junseo Lim To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau Cc: Stanislav Fomichev , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Sechang Lim Subject: [PATCH bpf v2 2/2] selftests/bpf: Exercise negative optlen in cgroup getsockopt hook Date: Tue, 11 Aug 2026 23:19:08 +0900 Message-ID: <4dbdcda23b2f2be06c5659f8102cd6bd036825b3.1786448307.git.zirajs7@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add a cgroup getsockopt selftest that sets ctx->optlen to -1. Use TCP_ZEROCOPY_RECEIVE to exercise the kernel-buffer getsockopt hook. The userspace-visible result is -EFAULT on both patched and unpatched kernels, so the return value alone cannot distinguish the bug. The test still exercises the kernel-buffer getsockopt path with a negative ctx->optlen, which reproduces the hardened usercopy warning on unpatched kernels. Signed-off-by: Junseo Lim --- Adding the selftest to sockopt_test triggered the problematic path, but detecting the broken behavior was not trivial because getsockopt() returned -EFAULT on both patched and unpatched kernels. The selftest mainly serves as a reproducer for the hardened usercopy warning. .../selftests/bpf/prog_tests/sockopt.c | 22 +++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/sockopt.c b/tools/testing/selftests/bpf/prog_tests/sockopt.c index eaac83a7f388..3834dcf0f9dd 100644 --- a/tools/testing/selftests/bpf/prog_tests/sockopt.c +++ b/tools/testing/selftests/bpf/prog_tests/sockopt.c @@ -1,4 +1,5 @@ // SPDX-License-Identifier: GPL-2.0 +#include #include #include #include "cgroup_helpers.h" @@ -283,6 +284,27 @@ static struct sockopt_test { .error = EFAULT_GETSOCKOPT, .io_uring_support = true, }, + { + .descr = "getsockopt: deny negative ctx->optlen in TCP_ZEROCOPY_RECEIVE", + .insns = { + /* ctx->optlen = -1 */ + BPF_MOV64_IMM(BPF_REG_0, -1), + BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0, + offsetof(struct bpf_sockopt, optlen)), + + /* return 1 */ + BPF_MOV64_IMM(BPF_REG_0, 1), + BPF_EXIT_INSN(), + }, + .attach_type = BPF_CGROUP_GETSOCKOPT, + .expected_attach_type = BPF_CGROUP_GETSOCKOPT, + + .get_level = IPPROTO_TCP, + .get_optname = TCP_ZEROCOPY_RECEIVE, + .get_optlen = sizeof(struct tcp_zerocopy_receive), + + .error = EFAULT_GETSOCKOPT, + }, { .descr = "getsockopt: ignore >PAGE_SIZE optlen", .insns = { -- 2.55.0