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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62FE1C433F5 for ; Wed, 6 Oct 2021 12:18:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4445861163 for ; Wed, 6 Oct 2021 12:18:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238468AbhJFMUX (ORCPT ); Wed, 6 Oct 2021 08:20:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35300 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238149AbhJFMUW (ORCPT ); Wed, 6 Oct 2021 08:20:22 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 37A03C061749; Wed, 6 Oct 2021 05:18:30 -0700 (PDT) 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=tuw64zH7FkvujlGPRt68jSX0rh3P5aIG7S452X6pvEs=; b=NUhlc4e3Ik4eh3/FI5sD9cWF57 hO0GMwe+ms4IofLbPAjMYIkq2HdbHZDK1b9wEqENhT16eCAHhpq1ymT1ZU6w3D0gFtnvnzSZV947F OD8d9NZPdhY9P8OAkjcgM78Owmys9wr+oJEfsaQrYG6ZtsJxDU1piwZ+avAzkgMYf5Au9fbPvk8zv iplHrgSSKofRKiO7LjuiyavTFkSVxvpgVoEs+9RR6R7Uzezf+BGRU2kvPyFPoDK9recZ8Vt+8nlQ0 hYs6P5Qqy6j/odYyL68/6laFK1bM9+Jg5BXtvmAo/q4cl81P6R0LDXyY4I0dOUiVHBkVr9TBOXgAL xk8CNmZw==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mY5rY-000rQ4-PP; Wed, 06 Oct 2021 12:17:40 +0000 Date: Wed, 6 Oct 2021 13:17:32 +0100 From: Matthew Wilcox To: Hao Sun Cc: Linux Kernel Mailing List , linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, Christoph Hellwig , Kees Cook Subject: Re: WARNING in __kernel_read Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 06, 2021 at 05:33:47PM +0800, Hao Sun wrote: > C reproducer: https://drive.google.com/file/d/1RzAsyIZzw5X_m340nY9fu4KWjGdG98pv/view?usp=sharing It's easier than this reproducer makes it look. res = syscall(__NR_openat, -1, 0x20000080ul, 0x4c003ul, 0x10ul); syscall(__NR_finit_module, r[0], 0ul, 3ul); should be enough. Basically, userspace opens an fd without FMODE_READ and passes it to finit_module(). > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 28082 at fs/read_write.c:429 > __kernel_read+0x3bb/0x410 fs/read_write.c:429 > Modules linked in: > CPU: 1 PID: 28082 Comm: syz-executor Not tainted 5.15.0-rc3+ #21 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 > RIP: 0010:__kernel_read+0x3bb/0x410 fs/read_write.c:429 > Call Trace: > kernel_read+0x47/0x60 fs/read_write.c:461 > kernel_read_file+0x20a/0x370 fs/kernel_read_file.c:93 > kernel_read_file_from_fd+0x55/0x90 fs/kernel_read_file.c:184 > __do_sys_finit_module+0x89/0x110 kernel/module.c:4180 finit_module() is not the only caller of kernel_read_file_from_fd() which passes it a fd that userspace passed in, for example kexec_file_load() doesn't validate the fd either. We could validate the fd in individual syscalls, in kernel_read_file_from_fd() or just do what vfs_read() does and return -EBADF without warning. So, one of these two patches. Christoph, Al, what's your preference? diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c index 87aac4c72c37..1f28b693d1db 100644 --- a/fs/kernel_read_file.c +++ b/fs/kernel_read_file.c @@ -178,7 +178,7 @@ int kernel_read_file_from_fd(int fd, loff_t offset, void **buf, struct fd f = fdget(fd); int ret = -EBADF; - if (!f.file) + if (!f.file || !(file->f_mode & FMODE_READ)) goto out; ret = kernel_read_file(f.file, offset, buf, buf_size, file_size, id); diff --git a/fs/read_write.c b/fs/read_write.c index af057c57bdc6..bab43b8532d1 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -426,8 +426,8 @@ ssize_t __kernel_read(struct file *file, void *buf, size_t count, loff_t *pos) struct iov_iter iter; ssize_t ret; - if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ))) - return -EINVAL; + if (!(file->f_mode & FMODE_READ)) + return -EBADF; if (!(file->f_mode & FMODE_CAN_READ)) return -EINVAL; /*