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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 C82DDC10DCE for ; Wed, 18 Mar 2020 16:39:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9CA6320767 for ; Wed, 18 Mar 2020 16:39:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584549583; bh=s7WMtHtSTQ/I40uZ0Ao4FX1zsUCtsqMIlS7BJUgnrA4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=H2v3WsZg4WckEjAAjQTRsSddVAImHL2oceo+Dge2bw+PYacgLAMroJsel938/sWBq DAP4aL9qEcs9vjZDtfZpLqIgQYEDCSDkWpTcMktS3Sd312H5NaVREesUB6BknlNWn3 KHicBchfL8aYYGcSzgjNjGg133ZtNscmAvM30m2U= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727238AbgCRQjn (ORCPT ); Wed, 18 Mar 2020 12:39:43 -0400 Received: from mail.kernel.org ([198.145.29.99]:50006 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727065AbgCRQjn (ORCPT ); Wed, 18 Mar 2020 12:39:43 -0400 Received: from sol.localdomain (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 21FB420752; Wed, 18 Mar 2020 16:39:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584549582; bh=s7WMtHtSTQ/I40uZ0Ao4FX1zsUCtsqMIlS7BJUgnrA4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=1XIxQCe2V1xPHNA+48U2QVBvhUcatTUYkKBIqnkevbdWIstMkS8YNMwMCG9JpXsln TGgtf3cTfrr90X+yPorLc2e+1cvcAFLM3jD+fuE80UYN9NNrDJH/JDCKlF79AhAd10 6cP8jP0h4PhFG+VovC391qQjtj0gTBEcOpelPSDg= Date: Wed, 18 Mar 2020 09:39:40 -0700 From: Eric Biggers To: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk Cc: glider@google.com, arnd@arndb.de, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, rafael@kernel.org, syzbot+fcab69d1ada3e8d6f06b@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com Subject: Re: [PATCH] libfs: fix infoleak in simple_attr_read() Message-ID: <20200318163940.GB2334@sol.localdomain> References: <20200308023849.988264-1-ebiggers@kernel.org> <20200313164511.GB907@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200313164511.GB907@sol.localdomain> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Mar 13, 2020 at 09:45:11AM -0700, Eric Biggers wrote: > On Sat, Mar 07, 2020 at 06:38:49PM -0800, Eric Biggers wrote: > > From: Eric Biggers > > > > Reading from a debugfs file at a nonzero position, without first reading > > at position 0, leaks uninitialized memory to userspace. > > > > It's a bit tricky to do this, since lseek() and pread() aren't allowed > > on these files, and write() doesn't update the position on them. But > > writing to them with splice() *does* update the position: > > > > #define _GNU_SOURCE 1 > > #include > > #include > > #include > > int main() > > { > > int pipes[2], fd, n, i; > > char buf[32]; > > > > pipe(pipes); > > write(pipes[1], "0", 1); > > fd = open("/sys/kernel/debug/fault_around_bytes", O_RDWR); > > splice(pipes[0], NULL, fd, NULL, 1, 0); > > n = read(fd, buf, sizeof(buf)); > > for (i = 0; i < n; i++) > > printf("%02x", buf[i]); > > printf("\n"); > > } > > > > Output: > > 5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a30 > > > > Fix the infoleak by making simple_attr_read() always fill > > simple_attr::get_buf if it hasn't been filled yet. > > > > Reported-by: syzbot+fcab69d1ada3e8d6f06b@syzkaller.appspotmail.com > > Reported-by: Alexander Potapenko > > Fixes: acaefc25d21f ("[PATCH] libfs: add simple attribute files") > > Cc: stable@vger.kernel.org > > Signed-off-by: Eric Biggers > > --- > > fs/libfs.c | 8 +++++--- > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/fs/libfs.c b/fs/libfs.c > > index c686bd9caac6..3759fbacf522 100644 > > --- a/fs/libfs.c > > +++ b/fs/libfs.c > > @@ -891,7 +891,7 @@ int simple_attr_open(struct inode *inode, struct file *file, > > { > > struct simple_attr *attr; > > > > - attr = kmalloc(sizeof(*attr), GFP_KERNEL); > > + attr = kzalloc(sizeof(*attr), GFP_KERNEL); > > if (!attr) > > return -ENOMEM; > > > > @@ -931,9 +931,11 @@ ssize_t simple_attr_read(struct file *file, char __user *buf, > > if (ret) > > return ret; > > > > - if (*ppos) { /* continued read */ > > + if (*ppos && attr->get_buf[0]) { > > + /* continued read */ > > size = strlen(attr->get_buf); > > - } else { /* first read */ > > + } else { > > + /* first read */ > > u64 val; > > ret = attr->get(attr->data, &val); > > if (ret) > > -- > > 2.25.1 > > Any comments on this? Al, seems this is something you should pick up? > > - Eric Ping.