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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 550E0C4167B for ; Sat, 12 Dec 2020 20:56:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1A2DC230FB for ; Sat, 12 Dec 2020 20:56:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407910AbgLLU4V (ORCPT ); Sat, 12 Dec 2020 15:56:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407890AbgLLU4U (ORCPT ); Sat, 12 Dec 2020 15:56:20 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A606BC0613CF; Sat, 12 Dec 2020 12:55:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=WvFf+jA75Sbv8N99WjSMJITzF6r6kvLC4AxYbTkoaMU=; b=pzSQ419n0/LzeB7FPfxuvjdg1b S+KMbAXTdTnw6SDA8CSdpfxIgeWbEoFXmLZIY5Q4KhhjNwHFcpz8n6hjPG4GTmAH5wdkzfngtMaVq doC3EYKNRYIzoBcoWdq/g71S7JEjPAFCgyPMWBJJYOGJRzMAXbnSlbLMq1kEkCMOeo0ssnaZHSWZg 8jruB4/ILM61wOfh2AXUsUZVQbAVUZmhJcF7AhI2AfKp030/D3yPmxW4z6Ac+HEGGXB3j8bTfq8UX Cdx/JUpCZTWPTMRDRidUP3OzTz4MgZ0+cH2yW0r43+wa/77saKX3wXQJCiugCWjC7jwRRkC3srPWz MARMV+pg==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1koBvG-0005AR-R6; Sat, 12 Dec 2020 20:55:22 +0000 Date: Sat, 12 Dec 2020 20:55:22 +0000 From: Matthew Wilcox To: Stephen Brennan Cc: Alexey Dobriyan , James Morris , "Serge E. Hallyn" , linux-security-module@vger.kernel.org, Paul Moore , Stephen Smalley , Eric Paris , selinux@vger.kernel.org, Casey Schaufler , Eric Biederman , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] proc: Allow pid_revalidate() during LOOKUP_RCU Message-ID: <20201212205522.GF2443@casper.infradead.org> References: <20201204000212.773032-1-stephen.s.brennan@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201204000212.773032-1-stephen.s.brennan@oracle.com> Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org On Thu, Dec 03, 2020 at 04:02:12PM -0800, Stephen Brennan wrote: > -void pid_update_inode(struct task_struct *task, struct inode *inode) > +static int do_pid_update_inode(struct task_struct *task, struct inode *inode, > + unsigned int flags) I'm really nitpicking here, but this function only _updates_ the inode if flags says it should. So I was thinking something like this (compile tested only). I'd really appreocate feedback from someone like Casey or Stephen on what they need for their security modules. diff --git a/fs/proc/base.c b/fs/proc/base.c index b362523a9829..771f330bfce7 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1968,6 +1968,25 @@ void pid_update_inode(struct task_struct *task, struct inode *inode) security_task_to_inode(task, inode); } +/* See if we can avoid the above call. Assumes RCU lock held */ +static bool inode_needs_pid_update(struct task_struct *task, + const struct inode *inode) +{ + kuid_t uid; + kgid_t gid; + + if (inode->i_mode & (S_ISUID | S_ISGID)) + return true; + task_dump_owner(task, inode->i_mode, &uid, &gid); + if (!uid_eq(uid, inode->i_uid) || !gid_eq(gid, inode->i_gid)) + return true; + /* + * XXX: Do we need to call the security system here to see if + * there's a pending update? + */ + return false; +} + /* * Rewrite the inode's ownerships here because the owning task may have * performed a setuid(), etc. @@ -1978,8 +1997,15 @@ static int pid_revalidate(struct dentry *dentry, unsigned int flags) struct inode *inode; struct task_struct *task; - if (flags & LOOKUP_RCU) + if (flags & LOOKUP_RCU) { + inode = d_inode_rcu(dentry); + task = pid_task(proc_pid(inode), PIDTYPE_PID); + if (!task) + return 0; + if (!inode_needs_pid_update(task, inode)) + return 1; return -ECHILD; + } inode = d_inode(dentry); task = get_proc_task(inode);