From patchwork Mon Jul 5 08:44:53 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marco Elver X-Patchwork-Id: 12358531 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 6F158C07E9B for ; Mon, 5 Jul 2021 08:45:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B52761405 for ; Mon, 5 Jul 2021 08:45:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230233AbhGEIrs (ORCPT ); Mon, 5 Jul 2021 04:47:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60132 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230211AbhGEIrq (ORCPT ); Mon, 5 Jul 2021 04:47:46 -0400 Received: from mail-ej1-x649.google.com (mail-ej1-x649.google.com [IPv6:2a00:1450:4864:20::649]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4A611C061762 for ; Mon, 5 Jul 2021 01:45:08 -0700 (PDT) Received: by mail-ej1-x649.google.com with SMTP id bz12-20020a1709070aacb02904cae86564c7so4883574ejc.6 for ; Mon, 05 Jul 2021 01:45:08 -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=4je/SN/KnbWSxzkZDr2TBnIQKjzyK1cJT3ltaKs0hSk=; b=gIPZ/pkiwQLpxzTFCRj21rl1/o+7fwZ6MTh3ps/+BfQ4hDEsI+00IeYjXdbZCxyIy/ 97UcdDClYYqsmf1N91dYrgdSUqkSwaOHLpzjPIg6K7dJyCPZuEeokHlRanhP06uSybrx dctiCkKkuUTG5eZ4xRycny6YX9ll83Y6u+YL5zM1FzYFUzWZ5ChDw5X+BLDworoi4Mlm rdv30/Tt1WjVXeMKpn3Doh0/Fr83nqAcR0n5rKMcPxgFEwN4tXahtK4ORjdl0nvrAfuX O3jywjaFZe1aflBqeqpKHQeGluwkHnC1A7dwRbq81+LUVKZyVzYxUvzQtveEL82+3BiE 425A== 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=4je/SN/KnbWSxzkZDr2TBnIQKjzyK1cJT3ltaKs0hSk=; b=MvkpwMMIcTaPWIE+lhVGL48X6NjC06h7Y0fEGZCenL8R5v3JP1h94ycvzl9db0lhJZ P+N/4X3Y0QiWBcT/31yQs3tMlycGXIiE6TC1f1uUd5u2e7tdnWyMv4EgmaajhqXJhPvR T4+NNSh3M8ylbrCCfOns27OADMXBi4ZDKH7gOphKcO8/hTkxGsYiFcDcptQ796uFkEli bW9rXLC43SF1VcKvP1o1GjRnlypheCK+qAc94yXyufcn7XCUdvR1JHxqBymveCEQzu/V FzTKjog1lKx71lFURC9NEKkzbOVqiE9RvGlj7v6Lm4ZtUtcJsw82pp6Vsxh4ZALzSQfE gvrQ== X-Gm-Message-State: AOAM530QEBB60ciYuk2in1jHEyL82+YBhODSAma3zXUmrJFL4Dhy/Y7Y 4lae0vWASNBjxywr+SSgqz7kJvQkRQ== X-Google-Smtp-Source: ABdhPJxI4Vy7qzVuBvs6X1tEvcku6i7mhTH0+TZK4QhpVyhH9UXVrgJkCPKCUfN2kGvT52m+NLGPbQx6hg== X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:dddd:647c:7745:e5f7]) (user=elver job=sendgmr) by 2002:a05:6402:845:: with SMTP id b5mr14691508edz.266.1625474706620; Mon, 05 Jul 2021 01:45:06 -0700 (PDT) Date: Mon, 5 Jul 2021 10:44:53 +0200 In-Reply-To: <20210705084453.2151729-1-elver@google.com> Message-Id: <20210705084453.2151729-2-elver@google.com> Mime-Version: 1.0 References: <20210705084453.2151729-1-elver@google.com> X-Mailer: git-send-email 2.32.0.93.g670b81a890-goog Subject: [PATCH v3 2/2] perf: Refactor permissions check into perf_check_permission() 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 Precedence: bulk List-ID: Refactor the permission check in perf_event_open() into a helper perf_check_permission(). This makes the permission check logic more readable (because we no longer have a negated disjunction). Add a comment mentioning the ptrace check also checks the uid. No functional change intended. Signed-off-by: Marco Elver Reviewed-by: Dmitry Vyukov --- v3: * Introduce this patch to refactor the permissions checking logic to make it more readable (reported by Eric W. Biederman). --- kernel/events/core.c | 58 ++++++++++++++++++++++++-------------------- 1 file changed, 32 insertions(+), 26 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index f79ee82e644a..3008b986994b 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -11912,6 +11912,37 @@ __perf_event_ctx_lock_double(struct perf_event *group_leader, return gctx; } +static bool +perf_check_permission(struct perf_event_attr *attr, struct task_struct *task) +{ + unsigned int ptrace_mode = PTRACE_MODE_READ_REALCREDS; + bool 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. The + * ptrace check also includes checks that the current task and other + * task have matching uids, and is therefore not done here explicitly. + */ + return is_capable || ptrace_may_access(task, ptrace_mode); +} + /** * sys_perf_event_open - open a performance event, associate it to a task/cpu * @@ -12152,43 +12183,18 @@ 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. - * * We must hold exec_update_lock across this and any potential * perf_install_in_context() call for this new event to * serialize against exec() altering our credentials (and the * perf_event_exit_task() that could imply). */ err = -EACCES; - if (!is_capable && !ptrace_may_access(task, ptrace_mode)) + if (!perf_check_permission(&attr, task)) goto err_cred; }