From patchwork Mon Jul 5 08:44:52 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marco Elver X-Patchwork-Id: 12358529 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=-26.7 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 94DD3C07E9A for ; Mon, 5 Jul 2021 08:45:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 70032613F6 for ; Mon, 5 Jul 2021 08:45:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230101AbhGEIrn (ORCPT ); Mon, 5 Jul 2021 04:47:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60116 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230164AbhGEIrn (ORCPT ); Mon, 5 Jul 2021 04:47:43 -0400 Received: from mail-lj1-x249.google.com (mail-lj1-x249.google.com [IPv6:2a00:1450:4864:20::249]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1A72CC061762 for ; Mon, 5 Jul 2021 01:45:06 -0700 (PDT) Received: by mail-lj1-x249.google.com with SMTP id z8-20020a2e8e880000b02901703789676bso7226984ljk.10 for ; Mon, 05 Jul 2021 01:45:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=XT1F6bsaZFgcmmxxyjZZuJTZD371QBzAaF2qKad4ZRA=; b=vN2Y2GrXM9wFYnK8wro/zQ6xDDmrrViyrbnBQ/4RMgPlUiGyKcoYBPaG1wATVX1mUc HLLbWWydLEqq+/RJ8CvpnNaii17d0JfOUVy3Mc9JbwsqeWqH7aKWjt7xHWqLYzdP6USq myjSXPGUDxoAoC8er0ihCXFL4B1umZj8KSlEd2WQOO/OF3SD6fsbJlMNS+levqcWDZtE P717hU7sFwpkOAu26fqpZOF5y9tekPitlEOa4PDHMpZcjdYNS0otmoJBrj16WB4XXwx7 yHqFBHAIswo7fFD3lYb5dIXaxP2ZnUxMyfYPPD+auIZzPgWS5+50kXLs82lARyxwGE1o 8LOg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=XT1F6bsaZFgcmmxxyjZZuJTZD371QBzAaF2qKad4ZRA=; b=KtxF4oBZggqj5jz3ucVlPWTz3jjImZnIY3Vlnbhvi4BwzFjRjxj/9/C0rgWaTXqqqK 4iP4Oo4r2JGHomP6m3+allmfcoXN+Wx9SlvgaqmwaECT9gW+BmGA32yjs83FhFDIylY7 jDZlGTDeI8EaQh/HAKQVSOY9f4AbwF5FSKGMJZhORMHJsr6ziBNGdjrTp2gbzEpuEHoy iU1WN9mSqnPyQomqtoSb84h8bKS7Vz5IUGkkOFjyMbbQfWqmmf+IC6Wzod63/umbxedC Q4uz+Ucd2MPrpALHrHEvyllhoSW1dlSVlPol+5UekERhNGzDXRQ9Rn3PLZ1U+hsGvVEA zfQA== X-Gm-Message-State: AOAM533ZB6tkWkNTebaxZVfMr3sAoW+x6fZF4nlgpwsLLxrJigiW3AqO QisNeHnBE21KtwrFh0JI+AMIrBsnuQ== X-Google-Smtp-Source: ABdhPJwJJ8IYO0yfnhbmAMrM9usbbtUz3OfJO2G4Ka8fzvRpGpNhtc7thfb1yiXSp6CO0GpfORq4d5EOjA== X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:dddd:647c:7745:e5f7]) (user=elver job=sendgmr) by 2002:a19:6d01:: with SMTP id i1mr10104024lfc.422.1625474704103; Mon, 05 Jul 2021 01:45:04 -0700 (PDT) Date: Mon, 5 Jul 2021 10:44:52 +0200 Message-Id: <20210705084453.2151729-1-elver@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.32.0.93.g670b81a890-goog Subject: [PATCH v3 1/2] perf: Fix required permissions if sigtrap is requested From: Marco Elver To: elver@google.com, peterz@infradead.org Cc: tglx@linutronix.de, mingo@kernel.org, dvyukov@google.com, glider@google.com, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, mingo@redhat.com, acme@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, linux-perf-users@vger.kernel.org, ebiederm@xmission.com, omosnace@redhat.com, serge@hallyn.com, linux-security-module@vger.kernel.org, stable@vger.kernel.org Precedence: bulk List-ID: If perf_event_open() is called with another task as target and perf_event_attr::sigtrap is set, and the target task's user does not match the calling user, also require the CAP_KILL capability or PTRACE_MODE_ATTACH permissions. Otherwise, with the CAP_PERFMON capability alone it would be possible for a user to send SIGTRAP signals via perf events to another user's tasks. This could potentially result in those tasks being terminated if they cannot handle SIGTRAP signals. Note: The check complements the existing capability check, but is not supposed to supersede the ptrace_may_access() check. At a high level we now have: capable of CAP_PERFMON and (CAP_KILL if sigtrap) OR ptrace_may_access(...) // also checks for same thread-group and uid Fixes: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events") Cc: # 5.13+ Reported-by: Dmitry Vyukov Signed-off-by: Marco Elver Acked-by: Dmitry Vyukov --- v3: * Upgrade ptrace mode check to ATTACH if attr.sigtrap, otherwise it's possible to change the target task (send signal) even if only read ptrace permissions were granted (reported by Eric W. Biederman). v2: https://lkml.kernel.org/r/20210701083842.580466-1-elver@google.com * Drop kill_capable() and just check CAP_KILL (reported by Ondrej Mosnacek). * Use ns_capable(__task_cred(task)->user_ns, CAP_KILL) to check for capability in target task's ns (reported by Ondrej Mosnacek). v1: https://lkml.kernel.org/r/20210630093709.3612997-1-elver@google.com --- kernel/events/core.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index fe88d6eea3c2..f79ee82e644a 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -12152,10 +12152,33 @@ SYSCALL_DEFINE5(perf_event_open, } if (task) { + unsigned int ptrace_mode = PTRACE_MODE_READ_REALCREDS; + bool is_capable; + err = down_read_interruptible(&task->signal->exec_update_lock); if (err) goto err_file; + is_capable = perfmon_capable(); + if (attr.sigtrap) { + /* + * perf_event_attr::sigtrap sends signals to the other + * task. Require the current task to also have + * CAP_KILL. + */ + rcu_read_lock(); + is_capable &= ns_capable(__task_cred(task)->user_ns, CAP_KILL); + rcu_read_unlock(); + + /* + * If the required capabilities aren't available, checks + * for ptrace permissions: upgrade to ATTACH, since + * sending signals can effectively change the target + * task. + */ + ptrace_mode = PTRACE_MODE_ATTACH_REALCREDS; + } + /* * Preserve ptrace permission check for backwards compatibility. * @@ -12165,7 +12188,7 @@ SYSCALL_DEFINE5(perf_event_open, * perf_event_exit_task() that could imply). */ err = -EACCES; - if (!perfmon_capable() && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) + if (!is_capable && !ptrace_may_access(task, ptrace_mode)) goto err_cred; }