From patchwork Thu Apr 13 13:33:51 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Aleksandr Mikhalitsyn X-Patchwork-Id: 13210316 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6027FC77B61 for ; Thu, 13 Apr 2023 13:38:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231641AbjDMNiK (ORCPT ); Thu, 13 Apr 2023 09:38:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37492 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231583AbjDMNh3 (ORCPT ); Thu, 13 Apr 2023 09:37:29 -0400 Received: from smtp-relay-internal-1.canonical.com (smtp-relay-internal-1.canonical.com [185.125.188.123]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F1B08C169 for ; Thu, 13 Apr 2023 06:35:16 -0700 (PDT) Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by smtp-relay-internal-1.canonical.com (Postfix) with ESMTPS id 1CB763F4D8 for ; Thu, 13 Apr 2023 13:34:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=canonical.com; s=20210705; t=1681392878; bh=rNULU6RAxGb0BQBeZqXiTKDNImvgPcuxWTYLoRGLo/w=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version:Content-Type; b=X0TvC3pb5hUaEzzjJSf2FiczF1/K7a/7T+nzTBs+nO473J0K/fZM5ENugrEOjico2 t0uTeBIXm3AepQyDl4tc341SU2sNvRDstszwt7++IyOLWd8E79j780NNX3z6hEIosF RTUYI/SEBVY47GzL+fdjzpiXO5DWkJViaF5AdUENNGuI8m6s1IkSZTMCe/xpNsykXU WMb5qUsiF1h241BPMpp7RkDdp2GCr5y4eafgTdRUNtB7b/EiSZ/S+5PiKTNfmOuD+b V2cs1eoryv5gPTjzAulizMUtxTJlmnuoEyDzJMexHrUFQsr3+W/UHb1TKs9SKfDZiW /IPxpp7w6aSgg== Received: by mail-ed1-f71.google.com with SMTP id r1-20020a50d681000000b0050504eaf919so2628254edi.8 for ; Thu, 13 Apr 2023 06:34:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1681392868; x=1683984868; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=rNULU6RAxGb0BQBeZqXiTKDNImvgPcuxWTYLoRGLo/w=; b=crSokVVWoJ3Uc6M1YTyBeAwrQRT4EvLCId28mjKNYNjLM5fzLz/WjTme2FwubihP58 /VH9Dez3QaStpIvSS0lcKcpA3mXN6/tfiS5JRq5TcG2goK7xu6xacVOIHLS610V7fgIW fEMhzURpjDLlJmiS2uu/wSkNQ+N8zEfeFJfLKERHZdzRqqklD8YO2YOTz8Ak+UTW9RN7 yTJFzSHGDcFO9IGFYbvHPt0Z2AGysQUH6xj2QTbp8UyjCtqFKCXHvNBOpJeJBi7n2n4D 5h8VnvFAH3Tw5AV9T/TeNWk1ismlqG6OSQP7N7qMqo16pIqHu3HUt4rGefLXej1NC0CZ 0xbQ== X-Gm-Message-State: AAQBX9czb2SfI4m6t6DozG4TikNR+ei8t7bI0d5lnaqKOpMHK31xgXeX okb2jRqx2duHiUJnMGiGgi4vMB64bDSQkivKAoVXrTITXW1AK9YAwFvulcW7L88It4MhCAFqnWt Xz1YuoTG+6r3O7DWSJv1WvMqJAlv1Ktj+EA== X-Received: by 2002:a17:906:4a94:b0:94a:67a9:6052 with SMTP id x20-20020a1709064a9400b0094a67a96052mr2534949eju.67.1681392868358; Thu, 13 Apr 2023 06:34:28 -0700 (PDT) X-Google-Smtp-Source: AKy350a4+fAjAw/1QDbyv41gi/1EMTYh6zw3QQsJ+TVo04/81Tcy15Y1w8vFTEKCKGgyb6/G4NvG5A== X-Received: by 2002:a17:906:4a94:b0:94a:67a9:6052 with SMTP id x20-20020a1709064a9400b0094a67a96052mr2534924eju.67.1681392868038; Thu, 13 Apr 2023 06:34:28 -0700 (PDT) Received: from amikhalitsyn.. ([95.91.208.118]) by smtp.gmail.com with ESMTPSA id et22-20020a170907295600b0094a966330fdsm976806ejc.211.2023.04.13.06.34.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Apr 2023 06:34:27 -0700 (PDT) From: Alexander Mikhalitsyn To: davem@davemloft.net Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, daniel@iogearbox.net, Alexander Mikhalitsyn , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Leon Romanovsky , David Ahern , Arnd Bergmann , Kees Cook , Christian Brauner , Kuniyuki Iwashima , Lennart Poettering , Luca Boccassi Subject: [PATCH net-next v4 0/4] Add SCM_PIDFD and SO_PEERPIDFD Date: Thu, 13 Apr 2023 15:33:51 +0200 Message-Id: <20230413133355.350571-1-aleksandr.mikhalitsyn@canonical.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org 1. Implement SCM_PIDFD, a new type of CMSG type analogical to SCM_CREDENTIALS, but it contains pidfd instead of plain pid, which allows programmers not to care about PID reuse problem. 2. Add SO_PEERPIDFD which allows to get pidfd of peer socket holder pidfd. This thing is direct analog of SO_PEERCRED which allows to get plain PID. 3. Add SCM_PIDFD / SO_PEERPIDFD kselftest Idea comes from UAPI kernel group: https://uapi-group.org/kernel-features/ Big thanks to Christian Brauner and Lennart Poettering for productive discussions about this and Luca Boccassi for testing and reviewing this. === Motivation behind this patchset Eric Dumazet raised a question: > It seems that we already can use pidfd_open() (since linux-5.3), and > pass the resulting fd in af_unix SCM_RIGHTS message ? Yes, it's possible, but it means that from the receiver side we need to trust the sent pidfd (in SCM_RIGHTS), or always use combination of SCM_RIGHTS+SCM_CREDENTIALS, then we can extract pidfd from SCM_RIGHTS, then acquire plain pid from pidfd and after compare it with the pid from SCM_CREDENTIALS. A few comments from other folks regarding this. Christian Brauner wrote: >Let me try and provide some of the missing background. >There are a range of use-cases where we would like to authenticate a >client through sockets without being susceptible to PID recycling >attacks. Currently, we can't do this as the race isn't fully fixable. >We can only apply mitigations. >What this patchset will allows us to do is to get a pidfd without the >client having to send us an fd explicitly via SCM_RIGHTS. As that's >already possibly as you correctly point out. >But for protocols like polkit this is quite important. Every message is >standalone and we would need to force a complete protocol change where >we would need to require that every client allocate and send a pidfd via >SCM_RIGHTS. That would also mean patching through all polkit users. >For something like systemd-journald where we provide logging facilities >and want to add metadata to the log we would also immensely benefit from >being able to get a receiver-side controlled pidfd. >With the message type we envisioned we don't need to change the sender >at all and can be safe against pid recycling. >Link: https://gitlab.freedesktop.org/polkit/polkit/-/merge_requests/154 >Link: https://uapi-group.org/kernel-features Lennart Poettering wrote: >So yes, this is of course possible, but it would mean the pidfd would >have to be transported as part of the user protocol, explicitly sent >by the sender. (Moreover, the receiver after receiving the pidfd would >then still have to somehow be able to prove that the pidfd it just >received actually refers to the peer's process and not some random >process. – this part is actually solvable in userspace, but ugly) >The big thing is simply that we want that the pidfd is associated >*implicity* with each AF_UNIX connection, not explicitly. A lot of >userspace already relies on this, both in the authentication area >(polkit) as well as in the logging area (systemd-journald). Right now >using the PID field from SO_PEERCREDS/SCM_CREDENTIALS is racy though >and very hard to get right. Making this available as pidfd too, would >solve this raciness, without otherwise changing semantics of it all: >receivers can still enable the creds stuff as they wish, and the data >is then implicitly appended to the connections/datagrams the sender >initiates. >Or to turn this around: things like polkit are typically used to >authenticate arbitrary dbus methods calls: some service implements a >dbus method call, and when an unprivileged client then issues that >call, it will take the client's info, go to polkit and ask it if this >is ok. If we wanted to send the pidfd as part of the protocol we >basically would have to extend every single method call to contain the >client's pidfd along with it as an additional argument, which would be >a massive undertaking: it would change the prototypes of basically >*all* methods a service defines… And that's just ugly. >Note that Alex' patch set doesn't expose anything that wasn't exposed >before, or attach, propagate what wasn't before. All it does, is make >the field already available anyway (the struct ucred .pid field) >available also in a better way (as a pidfd), to solve a variety of >races, with no effect on the protocol actually spoken within the >AF_UNIX transport. It's a seamless improvement of the status quo. === This patch series is on top of net-next tree with pidfd.file.api.v6.4 tag (from git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git) merged in. Git tree: https://github.com/mihalicyn/linux/tree/scm_pidfd Cc: "David S. Miller" Cc: Eric Dumazet Cc: Jakub Kicinski Cc: Paolo Abeni Cc: Leon Romanovsky Cc: David Ahern Cc: Arnd Bergmann Cc: Kees Cook Cc: Christian Brauner Cc: Kuniyuki Iwashima Cc: Lennart Poettering Cc: Luca Boccassi Tested-by: Luca Boccassi Alexander Mikhalitsyn (4): scm: add SO_PASSPIDFD and SCM_PIDFD net: socket: add sockopts blacklist for BPF cgroup hook net: core: add getsockopt SO_PEERPIDFD selftests: net: add SCM_PIDFD / SO_PEERPIDFD test arch/alpha/include/uapi/asm/socket.h | 3 + arch/mips/include/uapi/asm/socket.h | 3 + arch/parisc/include/uapi/asm/socket.h | 3 + arch/sparc/include/uapi/asm/socket.h | 3 + include/linux/net.h | 1 + include/linux/socket.h | 1 + include/net/scm.h | 39 +- include/uapi/asm-generic/socket.h | 3 + net/core/sock.c | 44 ++ net/mptcp/sockopt.c | 1 + net/socket.c | 45 +- net/unix/af_unix.c | 18 +- tools/include/uapi/asm-generic/socket.h | 3 + tools/testing/selftests/net/.gitignore | 1 + tools/testing/selftests/net/af_unix/Makefile | 2 +- .../testing/selftests/net/af_unix/scm_pidfd.c | 430 ++++++++++++++++++ 16 files changed, 589 insertions(+), 11 deletions(-) create mode 100644 tools/testing/selftests/net/af_unix/scm_pidfd.c