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[2001:8b0:7a5a:26ff:156:3a4f:da9f:497f]) by smtp.gmail.com with ESMTPSA id w3sm50929wmg.44.2020.06.08.09.22.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Jun 2020 09:22:54 -0700 (PDT) From: Lorenz Bauer To: Alexei Starovoitov , Daniel Borkmann , Shuah Khan , Andrii Nakryiko , Roman Gushchin Cc: kernel-team@cloudflare.com, Lorenz Bauer , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf] bpf: cgroup: allow multi-attach program to replace itself Date: Mon, 8 Jun 2020 17:22:01 +0100 Message-Id: <20200608162202.94002-1-lmb@cloudflare.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When using BPF_PROG_ATTACH to attach a program to a cgroup in BPF_F_ALLOW_MULTI mode, it is not possible to replace a program with itself. This is because the check for duplicate programs doesn't take the replacement program into account. Replacing a program with itself might seem weird, but it has some uses: first, it allows resetting the associated cgroup storage. Second, it makes the API consistent with the non-ALLOW_MULTI usage, where it is possible to replace a program with itself. Third, it aligns BPF_PROG_ATTACH with bpf_link, where replacing itself is also supported. Sice this code has been refactored a few times this change will only apply to v5.7 and later. Adjustments could be made to commit 1020c1f24a94 ("bpf: Simplify __cgroup_bpf_attach") and commit d7bf2c10af05 ("bpf: allocate cgroup storage entries on attaching bpf programs") as well as commit 324bda9e6c5a ("bpf: multi program support for cgroup+bpf") Signed-off-by: Lorenz Bauer Fixes: af6eea57437a ("bpf: Implement bpf_link-based cgroup BPF program attachment") --- kernel/bpf/cgroup.c | 2 +- .../testing/selftests/bpf/prog_tests/cgroup_attach_multi.c | 7 +++++++ 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index fdf7836750a3..4d76f16524cc 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -378,7 +378,7 @@ static struct bpf_prog_list *find_attach_entry(struct list_head *progs, } list_for_each_entry(pl, progs, node) { - if (prog && pl->prog == prog) + if (prog && pl->prog == prog && prog != replace_prog) /* disallow attaching the same prog twice */ return ERR_PTR(-EINVAL); if (link && pl->link == link) diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c b/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c index 139f8e82c7c6..b549fcfacc0b 100644 --- a/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c @@ -230,6 +230,13 @@ void test_cgroup_attach_multi(void) "prog_replace", "errno=%d\n", errno)) goto err; + /* replace program with itself */ + attach_opts.replace_prog_fd = allow_prog[6]; + if (CHECK(bpf_prog_attach_xattr(allow_prog[6], cg1, + BPF_CGROUP_INET_EGRESS, &attach_opts), + "prog_replace", "errno=%d\n", errno)) + goto err; + value = 0; CHECK_FAIL(bpf_map_update_elem(map_fd, &key, &value, 0)); CHECK_FAIL(system(PING_CMD)); -- 2.25.1