From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A5241C48BEA for ; Mon, 24 Jun 2019 16:24:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7CDE9205C9 for ; Mon, 24 Jun 2019 16:24:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="wEfx71v1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732074AbfFXQYy (ORCPT ); Mon, 24 Jun 2019 12:24:54 -0400 Received: from mail-pl1-f202.google.com ([209.85.214.202]:50404 "EHLO mail-pl1-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732073AbfFXQYy (ORCPT ); Mon, 24 Jun 2019 12:24:54 -0400 Received: by mail-pl1-f202.google.com with SMTP id 71so7575085pld.17 for ; Mon, 24 Jun 2019 09:24:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=PScmwSK+K9IB8yZqW06OWrhD6812WTEkgOnr9yWmmf4=; b=wEfx71v1btEOlvKmKmG4dkf1KGyws8CgL75i2MN8jxzFYdlqumo5TK3W+0T/ktO7k/ HwHeQ1f0wq9/FGsZMXF4PsxNBKLN0DQflEMUoIPj5MdFDnnAkZZtOtTo4fGx2a/4hT3c Gev0bUeqtsRN1DCThef+94kIX01/oQ5bUsrLuXrFART5/z7+gOkArdXJDtyyGSSCs8rK qRGBp8PF02XPgqBvvgVaE1vy+yodX0/bLieUqDu2Yi/rQgL0qsRUZE4mFapSn19Zx/2/ ah1UJZVEKEr1jOSK4F+1HbA0HSsKsLYtgBU9rKobFieW96WkuQL+3OGK6uLZ4Exli0V2 OunQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=PScmwSK+K9IB8yZqW06OWrhD6812WTEkgOnr9yWmmf4=; b=SPHoG4O2OeQ0UIUz35q3EoC2OTi/bEmZUyIemtvH34nXdQIxy3S6mN21W1hOI8YvgX y+RulnEEtQ9F1DLGR8ko8Y8s1h2/6dUVEfBkVxhbbIDscYz+x7iaPz0NSJDajhI/Dmxx kpT62G133mD0JUB6FjJi7Xnv7ljFaI5S30e7eXlM3yfJLIB9+eaIG9sQN/oEQpAfKbs6 SPpSmmECG4snqjt/v378xkGDpQ7RsCEhPvqswRZG3V91sO9QddrBS/rAa1fy7BC3C5hZ AL/aso8utoHJqt4IKPq5OqhcsAdCbuUqVoaIizNCEyWl1Z5HdkHiaLrPtD+Kd9mdtEwO eqgg== X-Gm-Message-State: APjAAAUoFsRV0huScK6ntR1Gd8AY6+kgKCgRHMfYsyrOPXi/p+Iv/JTM vHXDc8sD+zexNUWsXjWG7r96IKc= X-Google-Smtp-Source: APXvYqzMMHwmVqaFzQnYx7bu5yd1OmIKwA79DzoWPcErMHCvC7ljY+EnI7Uo/KFuXh+MSyIIpKQtQOU= X-Received: by 2002:a63:8043:: with SMTP id j64mr18485659pgd.216.1561393493248; Mon, 24 Jun 2019 09:24:53 -0700 (PDT) Date: Mon, 24 Jun 2019 09:24:28 -0700 In-Reply-To: <20190624162429.16367-1-sdf@google.com> Message-Id: <20190624162429.16367-9-sdf@google.com> Mime-Version: 1.0 References: <20190624162429.16367-1-sdf@google.com> X-Mailer: git-send-email 2.22.0.410.gd8fdbe21b5-goog Subject: [PATCH bpf-next v8 8/9] bpf: add sockopt documentation From: Stanislav Fomichev To: netdev@vger.kernel.org, bpf@vger.kernel.org Cc: davem@davemloft.net, ast@kernel.org, daniel@iogearbox.net, Stanislav Fomichev , Martin Lau Content-Type: text/plain; charset="UTF-8" Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Provide user documentation about sockopt prog type and cgroup hooks. v7: * add description for retval=0 and optlen=-1 v6: * describe cgroup chaining, add example v2: * use return code 2 for kernel bypass Cc: Martin Lau Signed-off-by: Stanislav Fomichev --- Documentation/bpf/index.rst | 1 + Documentation/bpf/prog_cgroup_sockopt.rst | 82 +++++++++++++++++++++++ 2 files changed, 83 insertions(+) create mode 100644 Documentation/bpf/prog_cgroup_sockopt.rst diff --git a/Documentation/bpf/index.rst b/Documentation/bpf/index.rst index d3fe4cac0c90..801a6ed3f2e5 100644 --- a/Documentation/bpf/index.rst +++ b/Documentation/bpf/index.rst @@ -42,6 +42,7 @@ Program types .. toctree:: :maxdepth: 1 + prog_cgroup_sockopt prog_cgroup_sysctl prog_flow_dissector diff --git a/Documentation/bpf/prog_cgroup_sockopt.rst b/Documentation/bpf/prog_cgroup_sockopt.rst new file mode 100644 index 000000000000..24985740711a --- /dev/null +++ b/Documentation/bpf/prog_cgroup_sockopt.rst @@ -0,0 +1,82 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================ +BPF_PROG_TYPE_CGROUP_SOCKOPT +============================ + +``BPF_PROG_TYPE_CGROUP_SOCKOPT`` program type can be attached to two +cgroup hooks: + +* ``BPF_CGROUP_GETSOCKOPT`` - called every time process executes ``getsockopt`` + system call. +* ``BPF_CGROUP_SETSOCKOPT`` - called every time process executes ``setsockopt`` + system call. + +The context (``struct bpf_sockopt``) has associated socket (``sk``) and +all input arguments: ``level``, ``optname``, ``optval`` and ``optlen``. + +BPF_CGROUP_SETSOCKOPT +===================== + +``BPF_CGROUP_SETSOCKOPT`` is triggered *before* the kernel handling of +sockopt and it has mostly read-only context (it can modify only ``optlen``). +This hook has access to cgroup and socket local storage. + +If BPF program sets ``optlen`` to -1, the control will be returned +back to the userspace after all other BPF programs in the cgroup +chain finish (i.e. kernel ``setsockopt`` handling will *not* be executed). + +Note, that the only acceptable value to set to ``optlen`` is -1. Any +other value will trigger ``EFAULT``. + +Return Type +----------- + +* ``0`` - reject the syscall, ``EPERM`` will be returned to the userspace. +* ``1`` - success, continue with next BPF program in the cgroup chain. + +BPF_CGROUP_GETSOCKOPT +===================== + +``BPF_CGROUP_GETSOCKOPT`` is triggered *after* the kernel handing of +sockopt. The BPF hook can observe ``optval``, ``optlen`` and ``retval`` +if it's interested in whatever kernel has returned. BPF hook can override +the values above, adjust ``optlen`` and reset ``retval`` to 0. If ``optlen`` +has been increased above initial ``setsockopt`` value (i.e. userspace +buffer is too small), ``EFAULT`` is returned. + +Note, that the only acceptable value to set to ``retval`` is 0 and the +original value that the kernel returned. Any other value will trigger +``EFAULT``. + +Return Type +----------- + +* ``0`` - reject the syscall, ``EPERM`` will be returned to the userspace. +* ``1`` - success: copy ``optval`` and ``optlen`` to userspace, return + ``retval`` from the syscall (note that this can be overwritten by + the BPF program from the parent cgroup). + +Cgroup Inheritance +================== + +Suppose, there is the following cgroup hierarchy where each cgroup +has ``BPF_CGROUP_GETSOCKOPT`` attached at each level with +``BPF_F_ALLOW_MULTI`` flag:: + + A (root, parent) + \ + B (child) + +When the application calls ``getsockopt`` syscall from the cgroup B, +the programs are executed from the bottom up: B, A. First program +(B) sees the result of kernel's ``getsockopt``. It can optionally +adjust ``optval``, ``optlen`` and reset ``retval`` to 0. After that +control will be passed to the second (A) program which will see the +same context as B including any potential modifications. + +Example +======= + +See ``tools/testing/selftests/bpf/progs/sockopt_sk.c`` for an example +of BPF program that handles socket options. -- 2.22.0.410.gd8fdbe21b5-goog