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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 42AD6C43613 for ; Sat, 22 Jun 2019 04:46:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0ED712075E for ; Sat, 22 Jun 2019 04:46:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725994AbfFVEqU (ORCPT ); Sat, 22 Jun 2019 00:46:20 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:60110 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725932AbfFVEqU (ORCPT ); Sat, 22 Jun 2019 00:46:20 -0400 Received: from fsav104.sakura.ne.jp (fsav104.sakura.ne.jp [27.133.134.231]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x5M4jYDG014763; Sat, 22 Jun 2019 13:45:34 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav104.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav104.sakura.ne.jp); Sat, 22 Jun 2019 13:45:34 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav104.sakura.ne.jp) Received: from [192.168.1.8] (softbank126012062002.bbtec.net [126.12.62.2]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id x5M4jTdw014737 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Sat, 22 Jun 2019 13:45:34 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets. To: Al Viro Cc: linux-fsdevel@vger.kernel.org, syzbot , jmorris@namei.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, serge@hallyn.com, syzkaller-bugs@googlegroups.com, takedakn@nttdata.co.jp, "David S. Miller" References: <0000000000004f43fa058a97f4d3@google.com> <201906060520.x565Kd8j017983@www262.sakura.ne.jp> <1b5722cc-adbc-035d-5ca1-9aa56e70d312@I-love.SAKURA.ne.jp> <20190618204933.GE17978@ZenIV.linux.org.uk> From: Tetsuo Handa Message-ID: <8f874b03-b129-205f-5f05-125479701275@i-love.sakura.ne.jp> Date: Sat, 22 Jun 2019 13:45:30 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190618204933.GE17978@ZenIV.linux.org.uk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On 2019/06/19 5:49, Al Viro wrote: > On Sun, Jun 16, 2019 at 03:49:00PM +0900, Tetsuo Handa wrote: >> Hello, Al. >> >> Q1: Do you agree that we should fix TOMOYO side rather than SOCKET_I()->sk >> management. > > You do realize that sockets are not unique in that respect, right? > All kinds of interesting stuff can be accessed via /proc/*/fd/*, and > it _can_ be closed under you. So I'd suggest checking how your code > copes with similar for pipes, FIFOs, epoll, etc., accessed that way... I know all kinds of interesting stuff can be accessed via /proc/*/fd/*, and it _can_ be closed under me. Regarding sockets, I was accessing "struct socket" memory and "struct sock" memory which are outside of "struct inode" memory. But regarding other objects, I am accessing "struct dentry" memory, "struct super_block" memory and "struct inode" memory. I'm expecting that these memory can't be kfree()d as long as "struct path" holds a reference. Is my expectation correct? > > We are _not_ going to be checking that in fs/open.c - the stuff found > via /proc/*/fd/* can have the associated file closed by the time > we get to calling ->open() and we won't know that until said call. OK. Then, fixing TOMOYO side is the correct way. > >> Q2: Do you see any problem with using f->f_path.dentry->d_inode ? >> Do we need to use d_backing_inode() or d_inode() ? > > Huh? What's wrong with file_inode(f), in the first place? And > just when can that be NULL, while we are at it? Oh, I was not aware of file_inode(). Thanks. > >>> static int tomoyo_inode_getattr(const struct path *path) >>> { >>> + /* It is not safe to call tomoyo_get_socket_name(). */ >>> + if (path->dentry->d_inode && S_ISSOCK(path->dentry->d_inode->i_mode)) >>> + return 0; > > Can that be called for a negative? > I check for NULL when I'm not sure it is guaranteed to hold a valid pointer. You meant "we are sure that path->dentry->d_inode is valid", don't you? By the way, "negative" associates with IS_ERR() range. I guess that "NULL" is the better name... Anyway, here is V2 patch. >From c63c4074300921d6d1c33c3b8dc9c84ebfededf5 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Sat, 22 Jun 2019 13:14:26 +0900 Subject: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets. syzbot is reporting that use of SOCKET_I()->sk from open() can result in use after free problem [1], for socket's inode is still reachable via /proc/pid/fd/n despite destruction of SOCKET_I()->sk already completed. But there is no point with calling security_file_open() on sockets because open("/proc/pid/fd/n", !O_PATH) on sockets fails with -ENXIO. There is some point with calling security_inode_getattr() on sockets because stat("/proc/pid/fd/n") and fstat(open("/proc/pid/fd/n", O_PATH)) are valid. If we want to access "struct sock"->sk_{family,type,protocol} fields, we will need to use security_socket_post_create() hook and security_inode_free() hook in order to remember these fields because security_sk_free() hook is called before the inode is destructed. But since information which can be protected by checking security_inode_getattr() on sockets is trivial, let's not be bothered by "struct inode"->i_security management. There is point with calling security_file_ioctl() on sockets. Since ioctl(open("/proc/pid/fd/n", O_PATH)) is invalid, security_file_ioctl() on sockets should remain safe. [1] https://syzkaller.appspot.com/bug?id=73d590010454403d55164cca23bd0565b1eb3b74 Signed-off-by: Tetsuo Handa Reported-by: syzbot --- security/tomoyo/tomoyo.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c index 716c92e..8ea3f5d 100644 --- a/security/tomoyo/tomoyo.c +++ b/security/tomoyo/tomoyo.c @@ -126,6 +126,9 @@ static int tomoyo_bprm_check_security(struct linux_binprm *bprm) */ static int tomoyo_inode_getattr(const struct path *path) { + /* It is not safe to call tomoyo_get_socket_name(). */ + if (S_ISSOCK(d_inode(path->dentry)->i_mode)) + return 0; return tomoyo_path_perm(TOMOYO_TYPE_GETATTR, path, NULL); } @@ -316,6 +319,9 @@ static int tomoyo_file_open(struct file *f) /* Don't check read permission here if called from do_execve(). */ if (current->in_execve) return 0; + /* Sockets can't be opened by open(). */ + if (S_ISSOCK(file_inode(f)->i_mode)) + return 0; return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path, f->f_flags); } -- 1.8.3.1